diff --git a/app/layout.tsx b/app/layout.tsx
index c419231..c1327e4 100644
--- a/app/layout.tsx
+++ b/app/layout.tsx
@@ -1,4 +1,5 @@
 import type { Metadata } from "next";
+import { Analytics } from "@vercel/analytics/next";
 import "./globals.css";
 import "./block-theme.css";
 import "./account.css";
@@ -13,6 +14,7 @@ import { I18nProvider } from "@/components/I18nProvider";
 import { getI18n } from "@/lib/i18n";
 import "./polish.css";
 import "./mobile-game.css";
+import "./multiplayer.css";
 import { SiteSettingsProvider } from "@/components/SiteSettingsProvider";
 import { initialSiteSettings } from "@/lib/site-settings";
 import { user } from "@/lib/supabase";
@@ -50,6 +52,7 @@ export default async function RootLayout({
             <LegacyPasswordNotice enabled={!!account?.email} />
           </SiteSettingsProvider>
         </I18nProvider>
+        <Analytics />
       </body>
     </html>
   );
diff --git a/app/multiplayer.css b/app/multiplayer.css
new file mode 100644
index 0000000..624afff
--- /dev/null
+++ b/app/multiplayer.css
@@ -0,0 +1,217 @@
+.multiplayer-settings,
+.multiplayer-join {
+  display: grid;
+  gap: 12px;
+  margin: 18px 0;
+}
+.multiplayer-settings label,
+.multiplayer-join label,
+.multiplayer-lobby > label {
+  font-weight: 650;
+}
+.multiplayer-settings input,
+.multiplayer-settings select,
+.multiplayer-join input,
+.multiplayer-invite input {
+  width: 100%;
+  min-height: 44px;
+  border: 1px solid var(--line, #35404c);
+  border-radius: 10px;
+  padding: 10px 12px;
+  color: inherit;
+  background: var(--panel, #1a222c);
+  font: inherit;
+}
+.multiplayer-settings select {
+  max-width: 160px;
+}
+.multiplayer-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 24px 5%;
+  gap: 20px;
+  border-bottom: 1px solid var(--line, #35404c);
+}
+.multiplayer-lobby {
+  max-width: 1000px;
+  min-height: 70vh;
+}
+.multiplayer-lobby .eyebrow,
+.multiplayer-lobby .lead {
+  display: flex;
+  gap: 10px;
+  align-items: center;
+  flex-wrap: wrap;
+}
+.multiplayer-join {
+  max-width: 480px;
+}
+.multiplayer-invite {
+  display: flex;
+  gap: 10px;
+  margin: 12px 0 28px;
+}
+.multiplayer-invite input {
+  min-width: 0;
+}
+.multiplayer-invite .button {
+  white-space: nowrap;
+  flex-shrink: 0;
+}
+.multiplayer-roster {
+  list-style: none;
+  padding: 0;
+  margin: 16px 0 24px;
+  display: grid;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 10px;
+}
+.multiplayer-roster li {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 16px;
+  border: 1px solid var(--line, #35404c);
+  border-radius: 12px;
+  gap: 12px;
+  overflow-wrap: anywhere;
+}
+.multiplayer-roster li > span {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  flex-wrap: wrap;
+}
+.multiplayer-table-wrap {
+  overflow-x: auto;
+  margin: 28px 0;
+}
+.multiplayer-final {
+  min-width: 650px;
+  width: 100%;
+}
+.multiplayer-final caption {
+  text-align: left;
+  font-weight: 650;
+  margin-bottom: 16px;
+}
+.multiplayer-final .multiplayer-you {
+  background: #8dce6614;
+}
+.multiplayer-scoreboard {
+  position: absolute;
+  z-index: 20;
+  left: 80px;
+  top: 100px;
+  width: 245px;
+  padding: 12px 16px;
+  border-radius: 12px;
+  background: rgba(26, 34, 44, 0.96);
+  color: var(--text);
+  box-shadow: 0 6px 24px #0002;
+  max-height: calc(100dvh - 190px);
+  overflow: auto;
+}
+.multiplayer-scoreboard summary {
+  cursor: pointer;
+  font-weight: 650;
+}
+.multiplayer-scoreboard summary svg {
+  display: inline-block;
+  vertical-align: middle;
+  margin-right: 4px;
+}
+.multiplayer-scoreboard ul {
+  list-style: none;
+  margin: 12px 0;
+  padding: 0;
+}
+.multiplayer-scoreboard li {
+  display: flex;
+  justify-content: space-between;
+  gap: 12px;
+  padding: 8px 0;
+  border-bottom: 1px solid var(--line);
+  overflow-wrap: anywhere;
+}
+.multiplayer-scoreboard li > span {
+  flex: 1;
+  min-width: 0;
+}
+.multiplayer-scoreboard li small {
+  display: block;
+  font-size: 11px;
+  opacity: 0.7;
+}
+.multiplayer-network,
+.multiplayer-waiting {
+  position: fixed;
+  z-index: 50;
+  bottom: 18px;
+  left: 50%;
+  transform: translateX(-50%);
+  width: max-content;
+  max-width: calc(100% - 32px);
+  border-radius: 10px;
+  background: var(--panel);
+  color: var(--text);
+  box-shadow: 0 6px 24px #0003;
+  padding: 12px 18px;
+  text-align: center;
+}
+.multiplayer-network {
+  z-index: 100;
+  top: 80px;
+  bottom: auto;
+  border: 1px solid #aa5040;
+}
+.multiplayer-round-result {
+  max-height: calc(100dvh - 100px);
+  overflow-y: auto;
+}
+.multiplayer-round-scores {
+  padding: 0;
+  margin: 12px 0 20px;
+  list-style: none;
+  text-align: left;
+}
+.multiplayer-round-scores li {
+  display: flex;
+  justify-content: space-between;
+  gap: 16px;
+  padding: 7px 0;
+  border-bottom: 1px solid var(--line);
+  overflow-wrap: anywhere;
+}
+@media (max-width: 640px) {
+  .multiplayer-header {
+    padding: 18px 5%;
+  }
+  .multiplayer-roster {
+    grid-template-columns: 1fr;
+  }
+  .multiplayer-invite {
+    flex-wrap: wrap;
+  }
+  .multiplayer-scoreboard {
+    top: 130px;
+    left: 64px;
+    width: min(220px, calc(100% - 80px));
+  }
+  .multiplayer-waiting {
+    bottom: 96px;
+  }
+  .multiplayer-game .game-header > .report-content {
+    display: none;
+  }
+  .multiplayer-round-result {
+    max-height: calc(100dvh - 48px);
+  }
+}
+
+.start-panel .tabs button {
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+}
diff --git a/app/multiplayer/[id]/page.tsx b/app/multiplayer/[id]/page.tsx
new file mode 100644
index 0000000..e65e58c
--- /dev/null
+++ b/app/multiplayer/[id]/page.tsx
@@ -0,0 +1,13 @@
+import { MultiplayerRoom } from "@/components/MultiplayerRoom";
+import { notFound } from "next/navigation";
+import { z } from "zod";
+
+export default async function MultiplayerPage({
+  params,
+}: {
+  params: Promise<{ id: string }>;
+}) {
+  const { id } = await params;
+  if (!z.string().uuid().safeParse(id).success) notFound();
+  return <MultiplayerRoom id={id} />;
+}
diff --git a/components/MultiplayerGame.tsx b/components/MultiplayerGame.tsx
new file mode 100644
index 0000000..8ca9c76
--- /dev/null
+++ b/components/MultiplayerGame.tsx
@@ -0,0 +1,314 @@
+"use client";
+
+import { useCallback, useEffect, useRef, useState } from "react";
+import {
+  Maximize2,
+  Minimize2,
+  MapPin,
+  Map as MapIcon,
+  Users,
+} from "lucide-react";
+import { Brand } from "./Brand";
+import { Panorama } from "./Panorama";
+import { GuessMap, type Pin } from "./GuessMap";
+import { ReportContent } from "./ReportContent";
+import { useI18n } from "./I18nProvider";
+import { api } from "@/lib/client-api";
+import { difficulties } from "@/shared/protocol";
+import type { RoomView, RoomMedia } from "@/shared/multiplayer";
+
+export function MultiplayerGame({
+  id,
+  room,
+  busy,
+  action,
+  remaining,
+  onLeave,
+}: {
+  id: string;
+  room: RoomView;
+  busy: boolean;
+  action: (type: string, payload?: object) => Promise<boolean>;
+  remaining: (deadline: string) => number;
+  onLeave: () => void;
+}) {
+  const { t, formatNumber } = useI18n();
+  const [media, setMedia] = useState<RoomMedia | null>(null);
+  const [error, setError] = useState("");
+  const [pin, setPin] = useState<Pin | null>(null);
+  const [expanded, setExpanded] = useState(false);
+  const [loaded, setLoaded] = useState({ panorama: false, map: false });
+  const [seconds, setSeconds] = useState(0);
+  const [nextIn, setNextIn] = useState(0);
+  const sendingReady = useRef(false);
+  const me = room.players.find((player) => player.id === room.you);
+  const turn = room.rounds[room.round];
+  const result = turn.results.find((result) => result.playerId === room.you);
+  const owner = room.hostId === room.you;
+  const submitted = me?.submitted ?? false;
+  const deadline = turn.deadline;
+  useEffect(() => {
+    let disposed = false;
+    api<RoomMedia>(`rooms/${id}/media`)
+      .then((next) => {
+        if (!disposed && next.round === room.round) setMedia(next);
+      })
+      .catch((failure) => {
+        if (!disposed) setError(failure.message);
+      });
+    return () => {
+      disposed = true;
+    };
+  }, [id, room.round]);
+  useEffect(() => {
+    if (
+      room.status !== "loading" ||
+      !loaded.panorama ||
+      !loaded.map ||
+      me?.ready ||
+      sendingReady.current ||
+      busy ||
+      error
+    )
+      return;
+    sendingReady.current = true;
+    void action("ready", { round: room.round }).finally(() => {
+      sendingReady.current = false;
+    });
+  }, [room.status, room.round, me?.ready, loaded, busy, error, action]);
+  useEffect(() => {
+    const tick = () => {
+      setSeconds(deadline ? remaining(deadline) : 0);
+      setNextIn(room.transitionAt ? remaining(room.transitionAt) : 0);
+    };
+    tick();
+    const timer = setInterval(tick, 250);
+    return () => clearInterval(timer);
+  }, [deadline, room.transitionAt, remaining]);
+  const panoramaReady = useCallback(
+    () => setLoaded((previous) => ({ ...previous, panorama: true })),
+    [],
+  );
+  const mapReady = useCallback(
+    () => setLoaded((previous) => ({ ...previous, map: true })),
+    [],
+  );
+  const mediaError = useCallback((message: string) => setError(message), []);
+  const roundScores = [...turn.results].sort((a, b) => b.score - a.score);
+  return (
+    <main className="game-page multiplayer-game">
+      {media && (
+        <Panorama
+          urls={media.faces}
+          zoom={difficulties[room.difficulty].zoom}
+          onReady={panoramaReady}
+          onError={mediaError}
+        />
+      )}
+      <div className="game-header">
+        <Brand />
+        <ReportContent datasetId={room.datasetId} />
+        <div className="game-info">
+          <div>
+            <small>{t("ROUND")}</small>
+            <strong>{room.round + 1} / 5</strong>
+          </div>
+          <div>
+            <small>{t("TIME LEFT")}</small>
+            <strong
+              className={
+                room.status === "playing" && seconds <= 10 ? "urgent" : ""
+              }
+            >
+              {room.status === "loading"
+                ? t("Loading…")
+                : `${Math.floor(seconds / 60)}:${String(seconds % 60).padStart(2, "0")}`}
+            </strong>
+          </div>
+          <div>
+            <small>{t("POINTS")}</small>
+            <strong>{formatNumber(me?.total ?? 0)}</strong>
+          </div>
+        </div>
+      </div>
+      <details className="multiplayer-scoreboard">
+        <summary>
+          <Users size={16} /> {t("Players")} · {room.playerCount}
+        </summary>
+        <ul>
+          {room.players.map((player) => (
+            <li key={player.id}>
+              <span>
+                {player.name}
+                {player.id === room.you && <small> {t("(you)")}</small>}
+                <small>
+                  {player.left
+                    ? t("Left room")
+                    : room.status === "loading"
+                      ? player.ready
+                        ? t("Ready")
+                        : t("Loading…")
+                      : player.submitted
+                        ? t("Guess submitted")
+                        : t("Guessing")}
+                </small>
+              </span>
+              <strong>{formatNumber(player.total)}</strong>
+            </li>
+          ))}
+        </ul>
+        <button className="text-link" onClick={onLeave} disabled={busy}>
+          {t("Leave room")}
+        </button>
+      </details>
+      {media && (
+        <div className={"game-map " + (expanded ? "expanded" : "")}>
+          <button
+            className="mobile-map-toggle"
+            aria-expanded={expanded}
+            aria-controls="multiplayer-guess-map"
+            onClick={() => setExpanded(true)}
+          >
+            <MapIcon size={20} aria-hidden="true" />
+            <span>{pin ? t("Edit your guess") : t("Open guess map")}</span>
+          </button>
+          <div className="game-map-content" id="multiplayer-guess-map">
+            <div className="map-topline">
+              <span>{t("↑ N · PLACE YOUR GUESS")}</span>
+              <button
+                aria-label={expanded ? t("Collapse map") : t("Expand map")}
+                onClick={() => setExpanded((value) => !value)}
+              >
+                {expanded ? <Minimize2 size={15} /> : <Maximize2 size={15} />}
+              </button>
+            </div>
+            <GuessMap
+              bounds={media.bounds}
+              image={media.map}
+              pin={result ? result.guess : (room.myGuess ?? pin)}
+              actual={result?.actual}
+              onPin={setPin}
+              onReady={mapReady}
+              onError={mediaError}
+              disabled={
+                room.status !== "playing" || submitted || busy || seconds === 0
+              }
+            />
+            <div className="map-actions">
+              <small>
+                {submitted
+                  ? t("Guess locked. Waiting for the other players.")
+                  : pin
+                    ? `X ${Math.round(pin.x)} · Z ${Math.round(pin.z)}`
+                    : t("Click the map to drop a pin")}
+              </small>
+              <button
+                className="button primary full"
+                disabled={
+                  !pin ||
+                  busy ||
+                  submitted ||
+                  room.status !== "playing" ||
+                  seconds === 0
+                }
+                onClick={() =>
+                  pin && void action("guess", { round: room.round, ...pin })
+                }
+              >
+                <MapPin size={15} />{" "}
+                {submitted ? t("Guess submitted") : t("Submit guess")}
+              </button>
+            </div>
+          </div>
+        </div>
+      )}
+      {room.status === "playing" && submitted && (
+        <div className="multiplayer-waiting" role="status">
+          {t("Guess locked. Waiting for the other players.")}
+        </div>
+      )}
+      {room.status === "playing" && seconds === 0 && !submitted && (
+        <div className="multiplayer-waiting" role="status">
+          {t("Time is up. Calculating round scores…")}
+        </div>
+      )}
+      {(!media ||
+        !loaded.panorama ||
+        !loaded.map ||
+        room.status === "loading") &&
+        !error &&
+        room.status !== "results" && (
+          <div className="game-loading">
+            <div className="loading-cube" />
+            <h2>{t("Preparing your expedition.")}</h2>
+            <p>
+              {loaded.panorama && loaded.map
+                ? t("Waiting for players to load the shared round…")
+                : t("Loading panorama and surface map…")}
+            </p>
+            {room.status === "loading" && (
+              <small>
+                {t("Starting within {seconds}s", { seconds: nextIn })}
+              </small>
+            )}
+          </div>
+        )}
+      {error && (
+        <div className="round-result" role="alert">
+          <h2>{t("Connection interrupted.")}</h2>
+          <p>{t(error)}</p>
+          <button
+            className="button primary"
+            onClick={() => window.location.reload()}
+          >
+            {t("Reconnect")}
+          </button>
+        </div>
+      )}
+      {room.status === "results" && !error && (
+        <div className="round-result multiplayer-round-result">
+          <span className="eyebrow">
+            {t("ROUND")} {room.round + 1} {t("COMPLETE")}
+          </span>
+          <h2>{t("Round standings")}</h2>
+          <div className="score">
+            {formatNumber(result?.score ?? 0)}
+            <small> / 5,000</small>
+          </div>
+          <p>
+            {result?.timedOut
+              ? t("The clock ran out. This round scores zero.")
+              : t("{count} blocks from the actual location.", {
+                  count: formatNumber(Math.round(result?.distance ?? 0)),
+                })}
+          </p>
+          <ol className="multiplayer-round-scores">
+            {roundScores.map((score) => (
+              <li key={score.playerId}>
+                <span>
+                  {
+                    room.players.find((player) => player.id === score.playerId)
+                      ?.name
+                  }
+                </span>
+                <strong>{formatNumber(score.score)}</strong>
+              </li>
+            ))}
+          </ol>
+          {owner && (
+            <button
+              className="button primary full"
+              disabled={busy}
+              onClick={() => void action("next", { round: room.round })}
+            >
+              {t("Next round")} →
+            </button>
+          )}
+          <p className="muted">
+            {t("Next round in {seconds}s", { seconds: nextIn })}
+          </p>
+        </div>
+      )}
+    </main>
+  );
+}
diff --git a/components/MultiplayerRoom.tsx b/components/MultiplayerRoom.tsx
new file mode 100644
index 0000000..8bc91f8
--- /dev/null
+++ b/components/MultiplayerRoom.tsx
@@ -0,0 +1,367 @@
+"use client";
+
+import { useCallback, useEffect, useRef, useState } from "react";
+import Link from "next/link";
+import { useRouter } from "next/navigation";
+import { Copy, Users, Crown, Trophy } from "lucide-react";
+import { Brand } from "./Brand";
+import { MultiplayerGame } from "./MultiplayerGame";
+import { useI18n } from "./I18nProvider";
+import { api } from "@/lib/client-api";
+import { roundClock } from "@/shared/round-clock";
+import type { RoomView } from "@/shared/multiplayer";
+
+export function MultiplayerRoom({ id }: { id: string }) {
+  const { t, formatNumber } = useI18n();
+  const router = useRouter();
+  const [room, setRoom] = useState<RoomView | null>(null);
+  const [error, setError] = useState("");
+  const [busy, setBusy] = useState(false);
+  const [name, setName] = useState("");
+  const [invite, setInvite] = useState("");
+  const [copied, setCopied] = useState(false);
+  const clock = useRef<ReturnType<typeof roundClock> | null>(null);
+  const version = useRef(0);
+  const acting = useRef(false);
+  const latest = useRef<RoomView | null>(null);
+  const accept = useCallback((next: RoomView, sentAt: number) => {
+    clock.current = roundClock(next.serverNow, sentAt, performance.now());
+    latest.current = next;
+    setRoom(next);
+    setError("");
+  }, []);
+  const load = useCallback(async () => {
+    if (acting.current) return;
+    const current = ++version.current;
+    const sentAt = performance.now();
+    try {
+      const next = await api<RoomView>(`rooms/${id}`);
+      if (current === version.current) accept(next, sentAt);
+    } catch (failure) {
+      if (current === version.current) setError((failure as Error).message);
+    }
+  }, [id, accept]);
+  useEffect(() => {
+    setInvite(`${window.location.origin}/multiplayer/${id}`);
+    let stopped = false;
+    let timer: ReturnType<typeof setTimeout>;
+    const poll = async () => {
+      await load();
+      if (
+        !stopped &&
+        !["finished", "closed"].includes(latest.current?.status ?? "")
+      )
+        timer = setTimeout(poll, document.hidden ? 5000 : 2000);
+    };
+    void poll();
+    const resume = () => {
+      if (!document.hidden) void load();
+    };
+    document.addEventListener("visibilitychange", resume);
+    return () => {
+      stopped = true;
+      version.current++;
+      clearTimeout(timer);
+      document.removeEventListener("visibilitychange", resume);
+    };
+  }, [id, load]);
+  const action = useCallback(
+    async (type: string, payload: object = {}) => {
+      if (acting.current) return false;
+      acting.current = true;
+      setBusy(true);
+      setError("");
+      const current = ++version.current;
+      const sentAt = performance.now();
+      try {
+        const next = await api<RoomView>(`rooms/${id}/${type}`, payload);
+        if (current === version.current) accept(next, sentAt);
+        return true;
+      } catch (failure) {
+        if (current === version.current) setError((failure as Error).message);
+        return false;
+      } finally {
+        acting.current = false;
+        setBusy(false);
+      }
+    },
+    [id, accept],
+  );
+  const remaining = useCallback(
+    (deadline: string) =>
+      clock.current?.remaining(deadline, performance.now()) ?? 0,
+    [],
+  );
+  async function leave() {
+    if (await action("leave")) router.push("/servers");
+  }
+  async function copyInvite() {
+    try {
+      await navigator.clipboard.writeText(invite);
+      setCopied(true);
+    } catch {
+      setError("Copy the invite link from the field below");
+    }
+  }
+  const activeGame =
+    !!room?.you && ["loading", "playing", "results"].includes(room.status);
+  if (activeGame && room)
+    return (
+      <>
+        <MultiplayerGame
+          key={room.round}
+          id={id}
+          room={room}
+          busy={busy}
+          action={action}
+          remaining={remaining}
+          onLeave={leave}
+        />
+        {error && (
+          <div className="multiplayer-network" role="alert">
+            {t(error)}{" "}
+            <button className="text-link" onClick={() => void load()}>
+              {t("Retry")}
+            </button>
+          </div>
+        )}
+      </>
+    );
+  const owner = !!room?.you && room.you === room.hostId;
+  const finished = room?.status === "finished";
+  const winners = room?.players.filter((player) => player.rank === 1) ?? [];
+  return (
+    <>
+      <header className="multiplayer-header">
+        <Brand />
+        <Link href="/servers" className="text-link">
+          {t("Play & maps")}
+        </Link>
+      </header>
+      <main className="section page-content multiplayer-lobby">
+        {error && (
+          <p className="error-message" role="alert">
+            {t(error)}{" "}
+            <button className="text-link" onClick={() => void load()}>
+              {t("Retry")}
+            </button>
+          </p>
+        )}
+        {!room ? (
+          <p className="muted">{t("Loading multiplayer room…")}</p>
+        ) : (
+          <>
+            <span className="eyebrow">
+              <Users size={16} /> {t("Multiplayer")} · {room.name}
+            </span>
+            <h1>
+              {finished
+                ? t("Final standings")
+                : room.status === "closed"
+                  ? t("This room is closed")
+                  : t("An expedition with friends.")}
+            </h1>
+            {!room.you && room.status === "lobby" && (
+              <form
+                className="multiplayer-join"
+                onSubmit={(event) => {
+                  event.preventDefault();
+                  void action("join", { displayName: name });
+                }}
+              >
+                <p className="lead">
+                  {t("Join your friends for five rounds on the same map.")}
+                </p>
+                <p>
+                  {t("{count} / {limit} players", {
+                    count: room.playerCount,
+                    limit: room.playerLimit,
+                  })}
+                </p>
+                <label htmlFor="join-player-name">
+                  {t("Your player name")}
+                </label>
+                <input
+                  id="join-player-name"
+                  value={name}
+                  onChange={(event) => setName(event.target.value)}
+                  minLength={2}
+                  maxLength={32}
+                  required
+                  autoComplete="nickname"
+                  placeholder={t("Enter a player name")}
+                  disabled={busy}
+                />
+                <button
+                  className="button primary"
+                  disabled={busy || room.playerCount >= room.playerLimit}
+                >
+                  {room.playerCount >= room.playerLimit
+                    ? t("This room is full")
+                    : t("Join room")}
+                </button>
+              </form>
+            )}
+            {!room.you && !["lobby", "closed"].includes(room.status) && (
+              <p className="lead">{t("This match has already started")}</p>
+            )}
+            {room.you && room.status === "lobby" && (
+              <>
+                <p className="lead">
+                  {owner
+                    ? t(
+                        "Share the invite link. Start when your friends arrive.",
+                      )
+                    : t("You’re in! Waiting for the room owner to start.")}
+                </p>
+                <label htmlFor="room-invite">{t("Invite link")}</label>
+                <div className="multiplayer-invite">
+                  <input
+                    id="room-invite"
+                    value={invite}
+                    readOnly
+                    onFocus={(event) => event.target.select()}
+                  />
+                  <button className="button" onClick={copyInvite}>
+                    <Copy size={16} /> {copied ? t("Copied!") : t("Copy link")}
+                  </button>
+                </div>
+                <h2>
+                  {t("{count} / {limit} players", {
+                    count: room.playerCount,
+                    limit: room.playerLimit,
+                  })}
+                </h2>
+                <ul className="multiplayer-roster">
+                  {room.players.map((player) => (
+                    <li key={player.id}>
+                      <span>
+                        {player.id === room.hostId && (
+                          <Crown size={17} aria-label={t("Room owner")} />
+                        )}{" "}
+                        {player.name}{" "}
+                        {player.id === room.you && <small>{t("(you)")}</small>}
+                      </span>
+                      {owner && player.id !== room.you && (
+                        <button
+                          className="text-link"
+                          disabled={busy}
+                          onClick={() =>
+                            void action("kick", { playerId: player.id })
+                          }
+                          aria-label={t("Remove {name}", { name: player.name })}
+                        >
+                          {t("Remove")}
+                        </button>
+                      )}
+                    </li>
+                  ))}
+                </ul>
+                <p className="muted">
+                  {t(
+                    "Everyone plays the same five locations. The most points wins; equal totals share a place.",
+                  )}
+                </p>
+                <div className="inline-actions">
+                  {owner && (
+                    <button
+                      className="button primary"
+                      disabled={busy || room.playerCount < 2}
+                      onClick={() => void action("start")}
+                    >
+                      {t("Start multiplayer match")}
+                    </button>
+                  )}
+                  <button className="button" disabled={busy} onClick={leave}>
+                    {t("Leave room")}
+                  </button>
+                  {owner && (
+                    <button
+                      className="text-link"
+                      disabled={busy}
+                      onClick={() => void action("close")}
+                    >
+                      {t("Close room")}
+                    </button>
+                  )}
+                </div>
+                {owner && room.playerCount < 2 && (
+                  <p className="muted">
+                    {t("Invite at least one friend before starting")}
+                  </p>
+                )}
+              </>
+            )}
+            {finished && room.you && (
+              <>
+                <p className="lead">
+                  <Trophy size={24} aria-hidden="true" />{" "}
+                  {winners.map((player) => player.name).join(" & ")} ·{" "}
+                  {t("{count} points", {
+                    count: formatNumber(winners[0]?.total ?? 0),
+                  })}
+                </p>
+                <div className="multiplayer-table-wrap">
+                  <table className="history-table multiplayer-final">
+                    <caption>{t("Five-round totals")}</caption>
+                    <thead>
+                      <tr>
+                        <th>{t("Place")}</th>
+                        <th>{t("Player")}</th>
+                        {room.rounds.map((turn) => (
+                          <th key={turn.number}>
+                            {t("Round")} {turn.number + 1}
+                          </th>
+                        ))}
+                        <th>{t("Total points")}</th>
+                      </tr>
+                    </thead>
+                    <tbody>
+                      {room.players.map((player) => (
+                        <tr
+                          key={player.id}
+                          className={
+                            player.id === room.you ? "multiplayer-you" : ""
+                          }
+                        >
+                          <td>{player.rank}</td>
+                          <td>
+                            {player.name}
+                            {player.left && <small> · {t("Left room")}</small>}
+                          </td>
+                          {room.rounds.map((turn) => (
+                            <td key={turn.number}>
+                              {formatNumber(
+                                turn.results.find(
+                                  (result) => result.playerId === player.id,
+                                )?.score ?? 0,
+                              )}
+                            </td>
+                          ))}
+                          <td>
+                            <strong>{formatNumber(player.total)}</strong>
+                          </td>
+                        </tr>
+                      ))}
+                    </tbody>
+                  </table>
+                </div>
+                <Link
+                  className="button primary"
+                  href={`/servers/${room.datasetId}`}
+                >
+                  {t("Play this map again")}
+                </Link>
+              </>
+            )}
+            {room.status === "closed" && (
+              <Link className="button primary" href="/servers">
+                {t("Another adventure →")}
+              </Link>
+            )}
+          </>
+        )}
+      </main>
+    </>
+  );
+}
diff --git a/components/StartGame.tsx b/components/StartGame.tsx
index 6937b09..87fe4be 100644
--- a/components/StartGame.tsx
+++ b/components/StartGame.tsx
@@ -3,13 +3,16 @@ import { useI18n } from "@/components/I18nProvider";
 
 import { useState } from "react";
 import { useRouter } from "next/navigation";
-import { ArrowRight, Timer, ZoomIn } from "lucide-react";
+import { ArrowRight, Timer, ZoomIn, Users } from "lucide-react";
 import { difficulties, type Difficulty } from "@/shared/protocol";
 import { api } from "@/lib/client-api";
 export { api } from "@/lib/client-api";
 export function StartGame({ datasetId }: { datasetId: string }) {
   const { t } = useI18n();
   const [difficulty, setDifficulty] = useState<Difficulty>("normal"),
+    [mode, setMode] = useState<"solo" | "multiplayer">("solo"),
+    [displayName, setDisplayName] = useState(""),
+    [playerLimit, setPlayerLimit] = useState(4),
     [loading, setLoading] = useState(false),
     [error, setError] = useState("");
   const router = useRouter();
@@ -17,11 +20,15 @@ export function StartGame({ datasetId }: { datasetId: string }) {
     setLoading(true);
     setError("");
     try {
-      const session = await api<{ id: string }>("sessions", {
-        datasetId,
-        difficulty,
-      });
-      router.push("/play/" + session.id);
+      const session = await api<{ id: string }>(
+        mode === "solo" ? "sessions" : "rooms",
+        {
+          datasetId,
+          difficulty,
+          ...(mode === "multiplayer" ? { displayName, playerLimit } : {}),
+        },
+      );
+      router.push((mode === "solo" ? "/play/" : "/multiplayer/") + session.id);
     } catch (e) {
       setError((e as Error).message);
       setLoading(false);
@@ -31,6 +38,24 @@ export function StartGame({ datasetId }: { datasetId: string }) {
     <div className="start-panel">
       <span className="eyebrow">{t("YOUR EXPEDITION")}</span>
       <h2>{t("Choose your challenge.")}</h2>
+      <div className="tabs" aria-label={t("Game mode")}>
+        <button
+          aria-pressed={mode === "solo"}
+          className={mode === "solo" ? "active" : ""}
+          disabled={loading}
+          onClick={() => setMode("solo")}
+        >
+          {t("Solo")}
+        </button>
+        <button
+          aria-pressed={mode === "multiplayer"}
+          className={mode === "multiplayer" ? "active" : ""}
+          disabled={loading}
+          onClick={() => setMode("multiplayer")}
+        >
+          <Users size={15} /> {t("Multiplayer")}
+        </button>
+      </div>
       <div className="difficulty-options">
         {Object.entries(difficulties).map(([key, value]) => (
           <button
@@ -55,12 +80,53 @@ export function StartGame({ datasetId }: { datasetId: string }) {
       <p className="muted">
         {t("5 rounds · 25,000 possible points · No movement")}
       </p>
+      {mode === "multiplayer" && (
+        <div className="multiplayer-settings">
+          <label htmlFor="room-display-name">{t("Your player name")}</label>
+          <input
+            id="room-display-name"
+            value={displayName}
+            onChange={(event) => setDisplayName(event.target.value)}
+            minLength={2}
+            maxLength={32}
+            placeholder={t("Enter a player name")}
+            autoComplete="nickname"
+            disabled={loading}
+          />
+          <label htmlFor="room-player-limit">
+            {t("Player limit (including you)")}
+          </label>
+          <select
+            id="room-player-limit"
+            value={playerLimit}
+            onChange={(event) => setPlayerLimit(Number(event.target.value))}
+            disabled={loading}
+          >
+            {Array.from({ length: 15 }, (_, i) => i + 2).map((count) => (
+              <option key={count} value={count}>
+                {count}
+              </option>
+            ))}
+          </select>
+          <p className="muted">
+            {t(
+              "Create a room, share the invite link, and start when your friends arrive.",
+            )}
+          </p>
+        </div>
+      )}
       <button
         className="button primary full"
         onClick={start}
-        disabled={loading}
+        disabled={
+          loading || (mode === "multiplayer" && displayName.trim().length < 2)
+        }
       >
-        {loading ? t("Preparing your world…") : t("Start exploring")}
+        {loading
+          ? t("Preparing your world…")
+          : mode === "multiplayer"
+            ? t("Create multiplayer room")
+            : t("Start exploring")}
         <ArrowRight size={17} />
       </button>
       {error && (
diff --git a/docs/multiplayer.md b/docs/multiplayer.md
new file mode 100644
index 0000000..2d6424e
--- /dev/null
+++ b/docs/multiplayer.md
@@ -0,0 +1,45 @@
+# Multiplayer rooms
+
+Open a published map, select **Multiplayer**, enter your player name, and choose
+a limit from 2 to 16 players, including yourself. Create the room and copy its
+invite link. Friends open that link, enter a name, and join. The owner starts
+the match once at least two players are present and can remove players from
+the lobby.
+
+Everyone plays the same five randomly selected locations with the selected
+difficulty. A round starts when active players have loaded its images, with a
+30-second loading grace period. The timer and scoring run in PostgreSQL;
+refreshing the page restores the same player, guess, and deadline. Guesses and
+scores are revealed when everyone submits or the timer expires. Missing guesses
+score zero. The owner can advance from the round standings, or the next round
+starts automatically after 20 seconds. The final table ranks total points;
+equal totals share a place.
+
+Players join without an account. A separate HttpOnly cookie identifies each
+browser, and the room link acts as the invitation. Only the server can access
+the room tables and functions. Clients receive the current round's signed
+images and completed results, never future locations or other players' guesses
+before a round closes. Leaving the lobby frees a place; leaving during a match
+retains the player's results and scores their remaining rounds as zero. If the
+owner leaves, ownership transfers to another remaining player.
+
+Room state refreshes every two seconds, or every five seconds in a hidden tab.
+Unfinished rooms expire after 24 hours. Multiplayer results are separate from
+the solo leaderboard.
+
+## Database and verification
+
+Apply `supabase/migrations/20261007071259_multiplayer_rooms.sql` to a new database
+before deploying the web update. It has already been applied to MineGeo's
+configured Supabase project. Deployments continue through `npm run deploy`
+without a Git-provider connection.
+
+- `npm test`: validation and existing regression checks.
+- `npm run test:multiplayer`: isolated PostgreSQL state, permission, and scoring
+  checks, using the existing `.data/sql-verification` PGlite installation.
+- `node scripts/test-multiplayer-http.mjs <site-origin>`: real API and Storage
+  verification, including five-round rankings and concurrent last-slot joins.
+  Requires local Supabase configuration; creates and removes its own test rooms.
+- `node scripts/test-multiplayer-browser.mjs <site-origin>`: desktop and mobile
+  invite, reconnect, map interaction, and five-round standings checks. Requires
+  Playwright Chromium; removes its own test room and saves screenshots locally.
diff --git a/docs/vercel-deployment.md b/docs/vercel-deployment.md
index 86ff123..9f981f0 100644
--- a/docs/vercel-deployment.md
+++ b/docs/vercel-deployment.md
@@ -21,5 +21,17 @@ Useful options:
 - `npm run deploy -- --preview`: create a preview deployment.
 - `npm run deploy -- --help`: show usage.
 
+Vercel Web Analytics is included in the root layout through
+`@vercel/analytics/next`, so page views and client-side navigation are tracked
+across the site. Enable Web Analytics in the MineGeo project's Analytics tab
+before deploying. After deployment, visit the site and navigate between pages
+to verify collection. Content blockers can prevent analytics requests.
+
+Analytics uses the existing Vercel project and requires no Git connection or
+additional Supabase credentials.
+
+Multiplayer uses the Supabase migration described in [multiplayer.md](multiplayer.md).
+Apply that migration to a new database before deploying the multiplayer web files.
+
 The script targets the existing MineGeo project. Set `VERCEL_PROJECT_ID` and
 `VERCEL_ORG_ID` to deploy a copy to another Vercel project.
diff --git a/lib/api.ts b/lib/api.ts
index 8475af5..fdec554 100644
--- a/lib/api.ts
+++ b/lib/api.ts
@@ -15,6 +15,7 @@ import { mediaUrl, mediaUrls } from "./catalog";
 import { ServiceError, checkServiceError } from "./service-error";
 import { requestOrigin, verifyOrigin } from "./request-origin";
 import { accountApi } from "./account-api";
+import { multiplayerApi } from "./multiplayer-api";
 import { contributionCutoff, reportSchema } from "../shared/moderation";
 import { siteSettingsSchema } from "../shared/site-settings";
 import { getSiteSettings } from "./site-settings";
@@ -109,6 +110,8 @@ export async function handle(request: NextRequest, path: string[]) {
     verifyOrigin(request);
     if (path[0] === "auth" || path[0] === "profile")
       return await accountApi(request, path, { jsonBody, limit });
+    if (path[0] === "rooms")
+      return await multiplayerApi(request, path, { jsonBody, limit });
     const client = admin(),
       method = request.method;
     if (path[0] === "site-settings" && path.length === 1 && method === "GET") {
diff --git a/lib/multiplayer-api.ts b/lib/multiplayer-api.ts
new file mode 100644
index 0000000..6809a16
--- /dev/null
+++ b/lib/multiplayer-api.ts
@@ -0,0 +1,137 @@
+import "server-only";
+import { createHash, randomBytes } from "node:crypto";
+import { NextRequest, NextResponse } from "next/server";
+import { z } from "zod";
+import { admin, required } from "./supabase";
+import { mediaUrls } from "./catalog";
+import { requestOrigin } from "./request-origin";
+import { ServiceError } from "./service-error";
+import {
+  createRoomSchema,
+  joinRoomSchema,
+  roomRoundSchema,
+  roomGuessSchema,
+  type RoomView,
+} from "../shared/multiplayer";
+import {
+  datasetSchema,
+  faces,
+  panoramaPath,
+  viewpointSchema,
+} from "../shared/protocol";
+
+type Dependencies = {
+  jsonBody: (request: NextRequest) => Promise<unknown>;
+  limit: (key: string, count: number, seconds: number) => Promise<void>;
+};
+const hash = (value: string) =>
+  createHash("sha256").update(value).digest("hex");
+
+export async function multiplayerApi(
+  request: NextRequest,
+  path: string[],
+  { jsonBody, limit }: Dependencies,
+) {
+  const client = admin();
+  const savedSecret = request.cookies.get("mg_multiplayer")?.value;
+  const secret = savedSecret || randomBytes(32).toString("hex");
+  const accessHash = hash(secret);
+  const respond = (body: unknown) => {
+    const response = NextResponse.json(body);
+    if (!savedSecret && request.method === "POST")
+      response.cookies.set("mg_multiplayer", secret, {
+        httpOnly: true,
+        sameSite: "lax",
+        secure: requestOrigin(request, process.env.MINEGEO_URL).startsWith(
+          "https:",
+        ),
+        path: "/",
+        maxAge: 60 * 60 * 24 * 30,
+      });
+    return response;
+  };
+  if (request.method === "POST" && path.length === 1) {
+    const body = createRoomSchema.parse(await jsonBody(request));
+    await limit("multiplayer:create:" + accessHash, 20, 3600);
+    const id = required(
+      await client.rpc("create_multiplayer_room", {
+        p_dataset: body.datasetId,
+        p_difficulty: body.difficulty,
+        p_name: body.displayName,
+        p_limit: body.playerLimit,
+        p_access_hash: accessHash,
+      }),
+    );
+    return respond({ id });
+  }
+  const id = z.string().uuid().parse(path[1]);
+  const action = path[2] ?? "view";
+  let payload: Record<string, string | number> = {};
+  if (request.method === "POST" && path.length === 3) {
+    const input = await jsonBody(request);
+    if (action === "join") {
+      payload = { name: joinRoomSchema.parse(input).displayName };
+      await limit("multiplayer:join:" + accessHash, 40, 3600);
+    } else if (action === "guess") payload = roomGuessSchema.parse(input);
+    else if (action === "ready" || action === "next")
+      payload = roomRoundSchema.parse(input);
+    else if (action === "kick")
+      payload = z.object({ playerId: z.string().uuid() }).parse(input);
+    else if (!["start", "leave", "close"].includes(action))
+      return NextResponse.json({ error: "Not found" }, { status: 404 });
+  } else if (
+    !(
+      request.method === "GET" &&
+      (path.length === 2 || (path.length === 3 && action === "media"))
+    )
+  )
+    return NextResponse.json({ error: "Not found" }, { status: 404 });
+
+  const room = required(
+    await client.rpc("multiplayer_action", {
+      p_room: id,
+      p_access_hash: accessHash,
+      p_action: request.method === "GET" ? "view" : action,
+      p_payload: payload,
+    }),
+  ) as unknown as RoomView;
+  if (action !== "media") return respond(room);
+  if (!room.you) throw new ServiceError("Join this room to play", 403);
+  if (["lobby", "closed"].includes(room.status))
+    throw new ServiceError("This round is not available yet", 409);
+
+  const [record, round] = await Promise.all([
+    client
+      .from("multiplayer_rooms")
+      .select("revision_id")
+      .eq("id", id)
+      .single(),
+    client
+      .from("multiplayer_rounds")
+      .select("viewpoint")
+      .eq("room_id", id)
+      .eq("round_number", room.round)
+      .single(),
+  ]);
+  const revision = required(
+    await client
+      .from("revisions")
+      .select("asset_root,manifest")
+      .eq("id", required(record).revision_id)
+      .single(),
+  );
+  const manifest = datasetSchema.parse(revision.manifest);
+  const viewpoint = viewpointSchema.parse(required(round).viewpoint);
+  const signed = await mediaUrls([
+    manifest.mapPath ?? `${revision.asset_root}/map.webp`,
+    ...faces.map((face) =>
+      panoramaPath(revision.asset_root, viewpoint, `${face}.webp`),
+    ),
+  ]);
+  return respond({
+    round: room.round,
+    bounds: manifest.bounds,
+    map: signed[0],
+    faces: signed.slice(1),
+  });
+}
diff --git a/package-lock.json b/package-lock.json
index 61547f1..d36a94c 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,6 +10,7 @@
       "dependencies": {
         "@supabase/ssr": "0.7.0",
         "@supabase/supabase-js": "2.117.2",
+        "@vercel/analytics": "2.0.1",
         "fflate": "0.8.3",
         "leaflet": "1.9.4",
         "lucide-react": "0.468.0",
@@ -1793,6 +1794,48 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@vercel/analytics": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/@vercel/analytics/-/analytics-2.0.1.tgz",
+      "integrity": "sha512-MTQG6V9qQrt1tsDeF+2Uoo5aPjqbVPys1xvnIftXSJYG2SrwXRHnqEvVoYID7BTruDz4lCd2Z7rM1BdkUehk2g==",
+      "license": "MIT",
+      "peerDependencies": {
+        "@remix-run/react": "^2",
+        "@sveltejs/kit": "^1 || ^2",
+        "next": ">= 13",
+        "nuxt": ">= 3",
+        "react": "^18 || ^19 || ^19.0.0-rc",
+        "svelte": ">= 4",
+        "vue": "^3",
+        "vue-router": "^4"
+      },
+      "peerDependenciesMeta": {
+        "@remix-run/react": {
+          "optional": true
+        },
+        "@sveltejs/kit": {
+          "optional": true
+        },
+        "next": {
+          "optional": true
+        },
+        "nuxt": {
+          "optional": true
+        },
+        "react": {
+          "optional": true
+        },
+        "svelte": {
+          "optional": true
+        },
+        "vue": {
+          "optional": true
+        },
+        "vue-router": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/@webgpu/types": {
       "version": "0.1.74",
       "resolved": "https://registry.npmjs.org/@webgpu/types/-/types-0.1.74.tgz",
diff --git a/package.json b/package.json
index 4bc0926..824f6aa 100644
--- a/package.json
+++ b/package.json
@@ -16,6 +16,7 @@
     "worker": "tsx worker/main.ts",
     "test": "tsx --test tests/*.test.ts",
     "test:leaderboard": "node scripts/test-leaderboard-sql.mjs",
+    "test:multiplayer": "node scripts/test-multiplayer-sql.mjs",
     "test:renderer": "node scripts/test-renderer.mjs",
     "render:map": "node scripts/render-map.mjs",
     "test:production": "node scripts/test-production.mjs",
@@ -27,6 +28,7 @@
   "dependencies": {
     "@supabase/ssr": "0.7.0",
     "@supabase/supabase-js": "2.117.2",
+    "@vercel/analytics": "2.0.1",
     "fflate": "0.8.3",
     "leaflet": "1.9.4",
     "lucide-react": "0.468.0",
diff --git a/scripts/test-multiplayer-browser.mjs b/scripts/test-multiplayer-browser.mjs
new file mode 100644
index 0000000..eb2b02c
--- /dev/null
+++ b/scripts/test-multiplayer-browser.mjs
@@ -0,0 +1,181 @@
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import { chromium, expect } from "@playwright/test";
+import { createClient } from "@supabase/supabase-js";
+if (fs.existsSync(".env.local")) process.loadEnvFile(".env.local");
+const origin = new URL(process.argv[2] || "http://127.0.0.1:3007").origin;
+const db = createClient(
+  process.env.NEXT_PUBLIC_SUPABASE_URL,
+  process.env.SUPABASE_SECRET_KEY,
+  { auth: { persistSession: false, autoRefreshToken: false } },
+);
+const rooms = [];
+const browser = await chromium.launch({
+  headless: true,
+  args: ["--use-angle=swiftshader", "--enable-unsafe-swiftshader"],
+});
+try {
+  const { data: maps, error } = await db
+    .from("datasets")
+    .select("id")
+    .eq("state", "published")
+    .limit(1);
+  if (error) throw error;
+  assert.ok(maps.length);
+  const desktop = await browser.newContext({
+    viewport: { width: 1280, height: 900 },
+    locale: "en-US",
+  });
+  const mobile = await browser.newContext({
+    viewport: { width: 390, height: 844 },
+    locale: "en-US",
+    isMobile: true,
+    hasTouch: true,
+  });
+  const host = await desktop.newPage(),
+    friend = await mobile.newPage();
+  const pageErrors = [];
+  for (const page of [host, friend])
+    page.on("pageerror", (error) => pageErrors.push(error.message));
+  await host.goto(`${origin}/servers/${maps[0].id}`, {
+    waitUntil: "networkidle",
+    timeout: 60000,
+  });
+  await host.getByRole("button", { name: "Multiplayer", exact: true }).click();
+  await host.getByLabel("Your player name").fill("Browser Host");
+  await host.getByLabel("Player limit (including you)").selectOption("2");
+  await host
+    .getByRole("button", { name: "Create multiplayer room", exact: true })
+    .click();
+  await host.waitForURL("**/multiplayer/*", { timeout: 30000 });
+  const id = host.url().split("/").pop();
+  rooms.push(id);
+  await expect(host.getByLabel("Invite link")).toHaveValue(
+    `${origin}/multiplayer/${id}`,
+  );
+  await friend.goto(host.url(), {
+    waitUntil: "domcontentloaded",
+    timeout: 60000,
+  });
+  await friend.getByLabel("Your player name").fill("Browser Friend");
+  await friend.getByRole("button", { name: "Join room", exact: true }).click();
+  await expect(
+    friend.getByText("You’re in! Waiting for the room owner to start.", {
+      exact: true,
+    }),
+  ).toBeVisible();
+  await expect(
+    host.getByRole("button", { name: "Start multiplayer match", exact: true }),
+  ).toBeEnabled({ timeout: 20000 });
+  fs.mkdirSync("artifacts/multiplayer", { recursive: true });
+  await host.screenshot({
+    path: "artifacts/multiplayer/desktop-lobby.png",
+    fullPage: true,
+  });
+  await friend.screenshot({
+    path: "artifacts/multiplayer/mobile-lobby.png",
+    fullPage: true,
+  });
+  assert.ok(
+    await friend.evaluate(
+      () => document.documentElement.scrollWidth <= window.innerWidth,
+    ),
+    "mobile lobby fits viewport",
+  );
+  await host
+    .getByRole("button", { name: "Start multiplayer match", exact: true })
+    .click();
+  for (let round = 0; round < 5; round++) {
+    await Promise.all([
+      expect(host.locator(".game-info strong").first()).toHaveText(
+        `${round + 1} / 5`,
+        { timeout: 30000 },
+      ),
+      expect(friend.locator(".game-info strong").first()).toHaveText(
+        `${round + 1} / 5`,
+        { timeout: 30000 },
+      ),
+    ]);
+    await Promise.all([
+      expect(host.locator(".game-loading")).toHaveCount(0, { timeout: 45000 }),
+      expect(friend.locator(".game-loading")).toHaveCount(0, {
+        timeout: 45000,
+      }),
+    ]);
+    if (round === 0) {
+      await host.reload({ waitUntil: "domcontentloaded" });
+      await expect(host.locator(".game-loading")).toHaveCount(0, {
+        timeout: 45000,
+      });
+    }
+    await friend
+      .getByRole("button", { name: "Open guess map", exact: true })
+      .click();
+    for (const [page, fraction] of [
+      [host, 0.48],
+      [friend, 0.7],
+    ]) {
+      const map = page.getByRole("application", { name: /Minecraft map/ });
+      const box = await map.boundingBox();
+      assert.ok(box);
+      await map.click({
+        position: { x: box.width * fraction, y: box.height * 0.5 },
+      });
+      await expect(
+        page.getByRole("button", { name: "Submit guess", exact: true }),
+      ).toBeEnabled();
+      if (round === 0 && page === host)
+        await page.screenshot({
+          path: "artifacts/multiplayer/desktop-round.png",
+        });
+      await page
+        .getByRole("button", { name: "Submit guess", exact: true })
+        .click();
+    }
+    if (round < 4) {
+      await expect(
+        host.getByRole("heading", { name: "Round standings", exact: true }),
+      ).toBeVisible({ timeout: 20000 });
+      await expect(
+        friend.getByRole("heading", { name: "Round standings", exact: true }),
+      ).toBeVisible({ timeout: 20000 });
+      await host.getByRole("button", { name: /^Next round/ }).click();
+    }
+    console.log(`Browser round ${round + 1}/5 completed.`);
+  }
+  await expect(
+    host.getByRole("heading", { name: "Final standings", exact: true }),
+  ).toBeVisible({ timeout: 20000 });
+  await expect(
+    friend.getByRole("heading", { name: "Final standings", exact: true }),
+  ).toBeVisible({ timeout: 20000 });
+  assert.equal(await host.locator(".multiplayer-final tbody tr").count(), 2);
+  await host.screenshot({
+    path: "artifacts/multiplayer/desktop-results.png",
+    fullPage: true,
+  });
+  await friend.screenshot({
+    path: "artifacts/multiplayer/mobile-results.png",
+    fullPage: true,
+  });
+  assert.ok(
+    await friend.evaluate(
+      () => document.documentElement.scrollWidth <= window.innerWidth,
+    ),
+    "mobile results fit viewport with table scrolling",
+  );
+  assert.deepEqual(pageErrors, []);
+  console.log(
+    "Desktop/mobile browser multiplayer passed: create, invite, join, reconnect, five shared rounds, map guesses, and final standings. No page errors.",
+  );
+} finally {
+  await browser.close();
+  if (rooms.length) {
+    const { error } = await db
+      .from("multiplayer_rooms")
+      .delete()
+      .in("id", rooms);
+    if (error)
+      throw new Error(`Browser test-room cleanup failed: ${error.message}`);
+  }
+}
diff --git a/scripts/test-multiplayer-http.mjs b/scripts/test-multiplayer-http.mjs
new file mode 100644
index 0000000..9952e09
--- /dev/null
+++ b/scripts/test-multiplayer-http.mjs
@@ -0,0 +1,163 @@
+import assert from "node:assert/strict";
+import { existsSync } from "node:fs";
+import { createClient } from "@supabase/supabase-js";
+if (existsSync(".env.local")) process.loadEnvFile(".env.local");
+const origin = new URL(process.argv[2] || "http://127.0.0.1:3007").origin;
+const db = createClient(
+  process.env.NEXT_PUBLIC_SUPABASE_URL,
+  process.env.SUPABASE_SECRET_KEY,
+  { auth: { persistSession: false, autoRefreshToken: false } },
+);
+const rooms = [];
+function player() {
+  let cookie;
+  return async (path, body, expected = 200) => {
+    const response = await fetch(`${origin}/api/v1/${path}`, {
+      method: body === undefined ? "GET" : "POST",
+      headers: {
+        ...(body === undefined
+          ? {}
+          : { origin, "content-type": "application/json" }),
+        ...(cookie ? { cookie } : {}),
+      },
+      body: body === undefined ? undefined : JSON.stringify(body),
+      signal: AbortSignal.timeout(30000),
+    });
+    if (response.headers.get("set-cookie"))
+      cookie = response.headers.get("set-cookie").split(";")[0];
+    const data = await response.json();
+    assert.equal(response.status, expected, JSON.stringify({ path, data }));
+    assert.match(response.headers.get("cache-control"), /no-store/);
+    return data;
+  };
+}
+try {
+  const host = player(),
+    friend = player(),
+    outsider = player();
+  const catalog = await host("catalog");
+  const datasetId = catalog.maps[0]?.id;
+  assert.ok(datasetId, "A published map is required");
+  const created = await host("rooms", {
+    datasetId,
+    difficulty: "hard",
+    displayName: "HTTP Host",
+    playerLimit: 2,
+  });
+  rooms.push(created.id);
+  const path = `rooms/${created.id}`;
+  const hostView = await host(path);
+  const preview = await outsider(path);
+  assert.equal(preview.you, null);
+  assert.deepEqual(preview.rounds, []);
+  await outsider(`${path}/media`, undefined, 403);
+  const joined = await friend(`${path}/join`, { displayName: "HTTP Friend" });
+  assert.equal(
+    (await friend(`${path}/join`, { displayName: "HTTP Other" })).you,
+    joined.you,
+  );
+  await outsider(`${path}/join`, { displayName: "Overflow" }, 400);
+  await friend(`${path}/start`, {}, 403);
+  await host(`${path}/start`, {});
+  let results;
+  for (let round = 0; round < 5; round++) {
+    const [hostMedia, friendMedia] = await Promise.all([
+      host(`${path}/media`),
+      friend(`${path}/media`),
+    ]);
+    assert.equal(hostMedia.round, round);
+    assert.equal(friendMedia.round, round);
+    assert.deepEqual(
+      hostMedia.faces.map((url) => new URL(url).pathname),
+      friendMedia.faces.map((url) => new URL(url).pathname),
+    );
+    assert.equal(hostMedia.faces.length, 6);
+    if (round === 0)
+      for (const url of [hostMedia.map, hostMedia.faces[0]])
+        assert.equal((await fetch(url)).status, 200, "Signed media readable");
+    await host(`${path}/ready`, { round });
+    const playing = await friend(`${path}/ready`, { round });
+    assert.equal(playing.status, "playing");
+    const synchronized = await host(path);
+    assert.equal(
+      synchronized.rounds[round].deadline,
+      playing.rounds[round].deadline,
+    );
+    const pointResult = await db
+      .from("multiplayer_rounds")
+      .select("viewpoint")
+      .eq("room_id", created.id)
+      .eq("round_number", round)
+      .single();
+    if (pointResult.error) throw pointResult.error;
+    const point = pointResult.data.viewpoint;
+    const first = await host(`${path}/guess`, {
+      round,
+      x: point.x,
+      z: point.z,
+    });
+    assert.equal(first.status, "playing");
+    assert.deepEqual(first.rounds[round].results, []);
+    assert.equal(
+      (await host(path)).players.find((p) => p.id === hostView.you).submitted,
+      true,
+      "Reconnect preserves submitted guess",
+    );
+    await host(`${path}/guess`, {
+      round,
+      x: hostMedia.bounds.minX,
+      z: hostMedia.bounds.minZ,
+    });
+    const b = hostMedia.bounds;
+    const x = point.x - (b.minX + b.maxX) / 2 >= 0 ? b.minX : b.maxX;
+    const z = point.z - (b.minZ + b.maxZ) / 2 >= 0 ? b.minZ : b.maxZ;
+    results = await friend(`${path}/guess`, { round, x, z });
+    assert.equal(results.status, round === 4 ? "finished" : "results");
+    assert.equal(
+      results.rounds[round].results.find((r) => r.playerId === hostView.you)
+        .score,
+      5000,
+    );
+    if (round < 4) await host(`${path}/next`, { round });
+  }
+  assert.equal(results.players[0].id, hostView.you);
+  assert.equal(results.players[0].total, 25000);
+  assert.equal(results.rounds.flatMap((round) => round.results).length, 10);
+  const capacityHost = player();
+  const full = await capacityHost("rooms", {
+    datasetId,
+    difficulty: "normal",
+    displayName: "Capacity Host",
+    playerLimit: 16,
+  });
+  rooms.push(full.id);
+  await Promise.all(
+    Array.from({ length: 14 }, (_, i) =>
+      player()(`rooms/${full.id}/join`, { displayName: `Capacity ${i + 2}` }),
+    ),
+  );
+  const attempts = await Promise.allSettled([
+    player()(`rooms/${full.id}/join`, { displayName: "Last A" }),
+    player()(`rooms/${full.id}/join`, { displayName: "Last B" }),
+  ]);
+  assert.equal(
+    attempts.filter((result) => result.status === "fulfilled").length,
+    1,
+    "Exactly one of the simultaneous last-slot joins succeeds",
+  );
+  const rejection = attempts.find((result) => result.status === "rejected");
+  assert.match(rejection.reason.message, /This room is full/);
+  assert.equal((await capacityHost(`rooms/${full.id}`)).playerCount, 16);
+  console.log(
+    "Multiplayer HTTP smoke passed: private invite joining, shared signed media and timers, five-round ranking, reconnects, retries, and simultaneous 16-player capacity checks.",
+  );
+} finally {
+  if (rooms.length) {
+    const { error } = await db
+      .from("multiplayer_rooms")
+      .delete()
+      .in("id", rooms);
+    if (error)
+      throw new Error(`Multiplayer test-room cleanup failed: ${error.message}`);
+  }
+}
diff --git a/scripts/test-multiplayer-sql.mjs b/scripts/test-multiplayer-sql.mjs
new file mode 100644
index 0000000..63dfbe1
--- /dev/null
+++ b/scripts/test-multiplayer-sql.mjs
@@ -0,0 +1,283 @@
+import assert from "node:assert/strict";
+import { readFile, readdir } from "node:fs/promises";
+import { PGlite } from "../.data/sql-verification/node_modules/@electric-sql/pglite/dist/index.js";
+
+// Isolated PostgreSQL: fixtures never enter production rooms or leaderboards.
+const db = new PGlite();
+try {
+  await db.exec(`create role anon; create role authenticated; create role service_role;
+    create schema auth; create table auth.users(id uuid primary key);
+    create function auth.uid() returns uuid language sql as $$ select null::uuid $$;
+    create schema storage; create table storage.buckets(id text primary key,name text,public boolean,file_size_limit bigint);`);
+  for (const file of (await readdir("supabase/migrations"))
+    .filter((file) => file.endsWith(".sql"))
+    .sort())
+    await db.exec(await readFile(`supabase/migrations/${file}`, "utf8"));
+  const account = (
+    await db.query(
+      "insert into auth.users values(gen_random_uuid()) returning id",
+    )
+  ).rows[0].id;
+  const dataset = (
+    await db.query(
+      `insert into public.datasets(owner_id,name,source,bounds,state,panorama_count)
+    values($1,'Multiplayer fixture','plugin','{"minX":0,"minZ":0,"maxX":64,"maxZ":64}','published',5) returning id`,
+      [account],
+    )
+  ).rows[0].id;
+  const manifest = {
+    name: "Multiplayer fixture",
+    bounds: { minX: 0, minZ: 0, maxX: 64, maxZ: 64 },
+    viewpoints: Array.from({ length: 5 }, (_, i) => ({
+      id: `point${i}`,
+      x: 10 + i,
+      z: 10 + i,
+      y: 64,
+    })),
+  };
+  const revision = (
+    await db.query(
+      "insert into public.revisions(dataset_id,asset_root,manifest) values($1,'fixture',$2) returning id",
+      [dataset, JSON.stringify(manifest)],
+    )
+  ).rows[0].id;
+  await db.query("update public.datasets set revision_id=$1 where id=$2", [
+    revision,
+    dataset,
+  ]);
+  const secret = (n) => String(n).padStart(64, "0");
+  async function create(cap = 2) {
+    return (
+      await db.query(
+        "select public.create_multiplayer_room($1,'hard','Host',$2,$3) as id",
+        [dataset, cap, secret(1)],
+      )
+    ).rows[0].id;
+  }
+  async function act(room, who, type = "view", payload = {}) {
+    return (
+      await db.query("select public.multiplayer_action($1,$2,$3,$4) as room", [
+        room,
+        secret(who),
+        type,
+        JSON.stringify(payload),
+      ])
+    ).rows[0].room;
+  }
+  for (const cap of [1, 17, null])
+    await assert.rejects(create(cap), /Choose between 2 and 16 players/);
+  const room = await create();
+  let view = await act(room, 1);
+  const host = view.you;
+  assert.equal(view.playerLimit, 2);
+  assert.equal(view.players.length, 1);
+  assert.equal(view.rounds.length, 5);
+  assert.ok(view.rounds.every((turn) => turn.results.length === 0));
+  const outsider = await act(room, 3);
+  assert.equal(outsider.you, null);
+  assert.deepEqual(outsider.players, []);
+  assert.deepEqual(outsider.rounds, []);
+  assert.ok(!JSON.stringify(view).includes('"viewpoint"'));
+  assert.ok(!JSON.stringify(view).includes("access_hash"));
+  await assert.rejects(act(room, 1, "start"), /Invite at least one friend/);
+  await assert.rejects(act(room, 3, "start"), /membership permission/);
+  const joined = await act(room, 2, "join", { name: "Friend" });
+  const friend = joined.you;
+  assert.equal(
+    (await act(room, 2, "join", { name: "Changed name" })).you,
+    friend,
+  );
+  await assert.rejects(act(room, 3, "join", { name: "Extra" }), /room is full/);
+  await assert.rejects(act(room, 2, "start"), /owner permission/);
+  view = await act(room, 1, "start");
+  assert.equal(view.status, "loading");
+  await assert.rejects(
+    act(room, 3, "join", { name: "Late" }),
+    /already started/,
+  );
+  await assert.rejects(
+    act(room, 1, "guess", { round: 0, x: 10, z: 10 }),
+    /Round is not active/,
+  );
+  assert.equal((await act(room, 1, "ready", { round: 0 })).status, "loading");
+  view = await act(room, 2, "ready", { round: 0 });
+  assert.equal(view.status, "playing");
+  const deadline = view.rounds[0].deadline;
+  assert.equal(
+    (await act(room, 1, "ready", { round: 0 })).rounds[0].deadline,
+    deadline,
+  );
+  await assert.rejects(
+    act(room, 1, "guess", { round: 0, x: 65, z: 0 }),
+    /Guess outside map/,
+  );
+  const location = (
+    await db.query(
+      "select viewpoint from public.multiplayer_rounds where room_id=$1 and round_number=0",
+      [room],
+    )
+  ).rows[0].viewpoint;
+  view = await act(room, 1, "guess", {
+    round: 0,
+    x: location.x,
+    z: location.z,
+  });
+  assert.equal(view.status, "playing");
+  assert.deepEqual(view.rounds[0].results, []);
+  assert.ok(
+    view.players.every((player) => player.total === 0),
+    "scores concealed until everyone finishes",
+  );
+  assert.deepEqual(view.myGuess, { x: location.x, z: location.z });
+  await act(room, 1, "guess", { round: 0, x: 0, z: 0 });
+  assert.equal(
+    (
+      await db.query(
+        "select count(*)::integer as count from public.multiplayer_guesses where room_id=$1 and player_id=$2",
+        [room, host],
+      )
+    ).rows[0].count,
+    1,
+  );
+  view = await act(room, 2, "guess", { round: 0, x: 0, z: 0 });
+  assert.equal(view.status, "results");
+  assert.equal(
+    view.rounds[0].results.find((result) => result.playerId === host).score,
+    5000,
+  );
+  assert.ok(
+    view.rounds[0].results.find((result) => result.playerId === friend).score <
+      5000,
+  );
+  await assert.rejects(act(room, 2, "next", { round: 0 }), /owner permission/);
+  assert.equal(
+    (await act(room, 1, "guess", { round: 0, x: 0, z: 0 })).status,
+    "results",
+    "retry cannot alter a submitted guess",
+  );
+  for (let round = 1; round < 5; round++) {
+    await act(room, 1, "next", { round: round - 1 });
+    await act(room, 1, "ready", { round });
+    await act(room, 2, "ready", { round });
+    const point = (
+      await db.query(
+        "select viewpoint from public.multiplayer_rounds where room_id=$1 and round_number=$2",
+        [room, round],
+      )
+    ).rows[0].viewpoint;
+    await act(room, 1, "guess", { round, x: point.x, z: point.z });
+    if (round === 2) {
+      await db.query(
+        "update public.multiplayer_rounds set deadline=clock_timestamp()-interval '1 second' where room_id=$1 and round_number=$2",
+        [room, round],
+      );
+      view = await act(room, 2, "guess", { round, x: point.x, z: point.z });
+      assert.equal(
+        view.rounds[round].results.find((result) => result.playerId === friend)
+          .score,
+        0,
+      );
+      assert.equal(
+        view.rounds[round].results.find((result) => result.playerId === friend)
+          .timedOut,
+        true,
+      );
+    } else view = await act(room, 2, "guess", { round, x: 0, z: 0 });
+  }
+  assert.equal(view.status, "finished");
+  assert.equal(view.players[0].id, host);
+  assert.equal(view.players[0].total, 25000);
+  assert.equal(view.players[0].rank, 1);
+  assert.equal(view.players[1].rank, 2);
+  assert.equal(view.rounds.flatMap((turn) => turn.results).length, 10);
+
+  const capacity = await create(16);
+  for (let n = 2; n <= 16; n++)
+    await act(capacity, n, "join", { name: `Player ${n}` });
+  await assert.rejects(
+    act(capacity, 17, "join", { name: "Overflow" }),
+    /room is full/,
+  );
+  assert.equal((await act(capacity, 1)).playerCount, 16);
+  const removed = (await act(capacity, 16)).you;
+  await act(capacity, 1, "kick", { playerId: removed });
+  assert.equal((await act(capacity, 16)).you, null);
+  await act(capacity, 17, "join", { name: "Replacement" });
+  await act(capacity, 1, "leave");
+  assert.equal(
+    (await act(capacity, 2)).hostId,
+    (await act(capacity, 2)).you,
+    "ownership transfers when host leaves",
+  );
+  await assert.rejects(
+    act(capacity, 18, "join", { name: "player 2" }),
+    /name is already taken/,
+  );
+
+  const stalled = await create();
+  await act(stalled, 2, "join", { name: "Offline" });
+  await act(stalled, 1, "start");
+  await act(stalled, 1, "ready", { round: 0 });
+  await db.query(
+    "update public.multiplayer_rooms set transition_at=clock_timestamp()-interval '1 second' where id=$1",
+    [stalled],
+  );
+  assert.equal(
+    (await act(stalled, 1)).status,
+    "playing",
+    "offline loader cannot block the match",
+  );
+  await db.query(
+    "update public.multiplayer_rounds set deadline=clock_timestamp()-interval '1 second' where room_id=$1 and round_number=0",
+    [stalled],
+  );
+  view = await act(stalled, 1);
+  assert.equal(view.status, "results");
+  assert.ok(
+    view.players.every((player) => player.rank === 1),
+    "equal totals share a rank",
+  );
+  await db.query(
+    "update public.multiplayer_rooms set transition_at=clock_timestamp()-interval '1 second' where id=$1",
+    [stalled],
+  );
+  assert.equal(
+    (await act(stalled, 1)).round,
+    1,
+    "rounds progress without host clicks",
+  );
+  await act(stalled, 2, "leave");
+  await act(stalled, 1, "ready", { round: 1 });
+  const point = (
+    await db.query(
+      "select viewpoint from public.multiplayer_rounds where room_id=$1 and round_number=1",
+      [stalled],
+    )
+  ).rows[0].viewpoint;
+  view = await act(stalled, 1, "guess", { round: 1, x: point.x, z: point.z });
+  assert.equal(view.status, "results", "departed players cannot block scoring");
+  await act(stalled, 1, "close");
+  assert.equal((await act(stalled, 1)).status, "closed");
+
+  for (const role of ["anon", "authenticated"]) {
+    await db.exec(`set role ${role}`);
+    for (const table of [
+      "multiplayer_rooms",
+      "multiplayer_players",
+      "multiplayer_rounds",
+      "multiplayer_guesses",
+    ])
+      await assert.rejects(
+        db.query(`select * from public.${table}`),
+        /permission denied/,
+      );
+    await assert.rejects(act(room, 1), /permission denied/);
+    await assert.rejects(create(), /permission denied/);
+    await db.exec("reset role");
+  }
+  console.log(
+    "Multiplayer SQL checks passed: 16-player cap, owner permissions, private answers, synchronized rounds, deadlines, retries, ties, departure, and client-role isolation.",
+  );
+} finally {
+  await db.close();
+}
diff --git a/shared/database.ts b/shared/database.ts
index 2a3ccde..cb30bc2 100644
--- a/shared/database.ts
+++ b/shared/database.ts
@@ -43,6 +43,93 @@ export type Database = {
   };
   public: {
     Tables: {
+      multiplayer_rooms: {
+        Row: {
+          id: string;
+          revision_id: string;
+          host_player_id: string;
+          difficulty: string;
+          player_limit: number;
+          status: string;
+          current_round: number;
+          transition_at: string | null;
+          created_at: string;
+        };
+        Insert: {
+          id?: string;
+          revision_id: string;
+          host_player_id: string;
+          difficulty: string;
+          player_limit: number;
+          status?: string;
+          current_round?: number;
+          transition_at?: string | null;
+          created_at?: string;
+        };
+        Update: {
+          host_player_id?: string;
+          status?: string;
+          current_round?: number;
+          transition_at?: string | null;
+        };
+        Relationships: [];
+      };
+      multiplayer_rounds: {
+        Row: {
+          room_id: string;
+          round_number: number;
+          viewpoint: Json;
+          deadline: string | null;
+          closed_at: string | null;
+        };
+        Insert: {
+          room_id: string;
+          round_number: number;
+          viewpoint: Json;
+          deadline?: string | null;
+          closed_at?: string | null;
+        };
+        Update: { deadline?: string | null; closed_at?: string | null };
+        Relationships: [];
+      };
+      multiplayer_players: {
+        Row: {
+          id: string;
+          room_id: string;
+          access_hash: string;
+          display_name: string;
+          ready_round: number;
+          has_left: boolean;
+          joined_at: string;
+        };
+        Insert: {
+          id?: string;
+          room_id: string;
+          access_hash: string;
+          display_name: string;
+          ready_round?: number;
+          has_left?: boolean;
+          joined_at?: string;
+        };
+        Update: { ready_round?: number; has_left?: boolean };
+        Relationships: [];
+      };
+      multiplayer_guesses: {
+        Row: {
+          room_id: string;
+          player_id: string;
+          round_number: number;
+          result: Json;
+        };
+        Insert: {
+          room_id: string;
+          player_id: string;
+          round_number: number;
+          result: Json;
+        };
+        Update: { result?: Json };
+        Relationships: [];
+      };
       site_settings: {
         Row: {
           id: boolean;
@@ -540,6 +627,25 @@ export type Database = {
       [_ in never]: never;
     };
     Functions: {
+      create_multiplayer_room: {
+        Args: {
+          p_dataset: string;
+          p_difficulty: string;
+          p_name: string;
+          p_limit: number;
+          p_access_hash: string;
+        };
+        Returns: string;
+      };
+      multiplayer_action: {
+        Args: {
+          p_room: string;
+          p_access_hash: string;
+          p_action: string;
+          p_payload: Json;
+        };
+        Returns: Json;
+      };
       legacy_password_needed: { Args: { p_user: string }; Returns: boolean };
       claim_legacy_password: { Args: { p_user: string }; Returns: boolean };
       set_beta_badge: {
diff --git a/shared/locales/ru.json b/shared/locales/ru.json
index b4a2f89..42e4a8f 100644
--- a/shared/locales/ru.json
+++ b/shared/locales/ru.json
@@ -605,5 +605,64 @@
   "Not now": "Не сейчас",
   "Select the password and copy it manually.": "Выдели пароль и скопируй его вручную.",
   "A password is already set or was already issued. Use password recovery if needed.": "Пароль уже установлен или был выдан ранее. Если нужно, воспользуйся восстановлением пароля.",
-  "Password setup could not be confirmed. Use password recovery before signing out.": "Не удалось подтвердить установку пароля. Восстанови пароль перед выходом из аккаунта."
+  "Password setup could not be confirmed. Use password recovery before signing out.": "Не удалось подтвердить установку пароля. Восстанови пароль перед выходом из аккаунта.",
+  "Game mode": "Режим игры",
+  "Solo": "Одиночная игра",
+  "Multiplayer": "Мультиплеер",
+  "Your player name": "Ваше игровое имя",
+  "Enter a player name": "Введите игровое имя",
+  "Player limit (including you)": "Лимит игроков (включая вас)",
+  "Create a room, share the invite link, and start when your friends arrive.": "Создайте комнату, поделитесь ссылкой и начните игру, когда друзья присоединятся.",
+  "Create multiplayer room": "Создать комнату",
+  "Retry": "Повторить",
+  "Loading multiplayer room…": "Загрузка комнаты…",
+  "Final standings": "Итоговая таблица",
+  "This room is closed": "Эта комната закрыта",
+  "An expedition with friends.": "Экспедиция с друзьями.",
+  "Join your friends for five rounds on the same map.": "Присоединитесь к друзьям: пять раундов на одной карте.",
+  "{count} / {limit} players": "Игроков: {count} / {limit}",
+  "This room is full": "Комната заполнена",
+  "Join room": "Войти в комнату",
+  "This match has already started": "Игра уже началась",
+  "Share the invite link. Start when your friends arrive.": "Поделитесь ссылкой. Начните игру, когда друзья присоединятся.",
+  "You’re in! Waiting for the room owner to start.": "Вы в комнате! Ждём, когда владелец начнёт игру.",
+  "Invite link": "Ссылка-приглашение",
+  "Copied!": "Скопировано!",
+  "Copy link": "Копировать ссылку",
+  "Room owner": "Владелец комнаты",
+  "(you)": "(вы)",
+  "Remove {name}": "Удалить игрока {name}",
+  "Remove": "Удалить",
+  "Everyone plays the same five locations. The most points wins; equal totals share a place.": "Все играют на одинаковых пяти локациях. Побеждает игрок с наибольшим числом очков; при равном счёте место общее.",
+  "Start multiplayer match": "Начать игру",
+  "Leave room": "Покинуть комнату",
+  "Close room": "Закрыть комнату",
+  "Invite at least one friend before starting": "Перед началом пригласите хотя бы одного друга",
+  "{count} points": "{count} очков",
+  "Five-round totals": "Результаты пяти раундов",
+  "Place": "Место",
+  "Player": "Игрок",
+  "Total points": "Всего очков",
+  "Left room": "Покинул комнату",
+  "Play this map again": "Сыграть на этой карте ещё раз",
+  "Loading…": "Загрузка…",
+  "Players": "Игроки",
+  "Ready": "Готов",
+  "Guess submitted": "Ответ отправлен",
+  "Guessing": "Выбирает место",
+  "Guess locked. Waiting for the other players.": "Ответ принят. Ждём остальных игроков.",
+  "Time is up. Calculating round scores…": "Время вышло. Подсчитываем очки…",
+  "Waiting for players to load the shared round…": "Ждём загрузки раунда у остальных игроков…",
+  "Starting within {seconds}s": "Начало не позднее чем через {seconds} с",
+  "Round standings": "Результаты раунда",
+  "Next round in {seconds}s": "Следующий раунд через {seconds} с",
+  "Copy the invite link from the field below": "Скопируйте ссылку из поля ниже",
+  "Choose between 2 and 16 players": "Выберите от 2 до 16 игроков",
+  "This name is already taken in this room": "Это имя уже занято в комнате",
+  "Room owner permission required": "Это действие доступно владельцу комнаты",
+  "Room membership permission required": "Сначала присоединитесь к комнате",
+  "Room not found": "Комната не найдена",
+  "Join this room to play": "Присоединитесь к комнате, чтобы играть",
+  "Wait for the round to finish": "Дождитесь завершения раунда",
+  "Players can only be removed before the match starts": "Удалять игроков можно только до начала игры"
 }
diff --git a/shared/multiplayer.ts b/shared/multiplayer.ts
new file mode 100644
index 0000000..f4596a9
--- /dev/null
+++ b/shared/multiplayer.ts
@@ -0,0 +1,62 @@
+import { z } from "zod";
+import { displayNameSchema } from "./account";
+import type { Bounds, Difficulty } from "./protocol";
+
+export const createRoomSchema = z.object({
+  datasetId: z.string().uuid(),
+  difficulty: z.enum(["easy", "normal", "hard"]),
+  displayName: displayNameSchema,
+  playerLimit: z.number().int().min(2).max(16),
+});
+export const joinRoomSchema = z.object({ displayName: displayNameSchema });
+export const roomRoundSchema = z.object({
+  round: z.number().int().min(0).max(4),
+});
+export const roomGuessSchema = roomRoundSchema.extend({
+  x: z.number().finite(),
+  z: z.number().finite(),
+});
+export type RoomResult = {
+  playerId: string;
+  score: number;
+  distance: number | null;
+  timedOut: boolean;
+  actual: { x: number; z: number };
+  guess: { x: number; z: number } | null;
+};
+export type RoomView = {
+  id: string;
+  datasetId: string;
+  name: string;
+  difficulty: Difficulty;
+  playerLimit: number;
+  playerCount: number;
+  status: "lobby" | "loading" | "playing" | "results" | "finished" | "closed";
+  round: number;
+  hostId: string;
+  you: string | null;
+  serverNow: number;
+  transitionAt: string | null;
+  players: {
+    id: string;
+    name: string;
+    left: boolean;
+    ready: boolean;
+    submitted: boolean;
+    total: number;
+    rank: number;
+  }[];
+  rounds: {
+    number: number;
+    deadline: string | null;
+    closedAt: string | null;
+    results: RoomResult[];
+  }[];
+  myGuess: { x: number; z: number } | null;
+};
+export type RoomMedia = {
+  round: number;
+  map: string;
+  bounds: Bounds;
+  faces: string[];
+};
diff --git a/supabase/migrations/20261007071259_multiplayer_rooms.sql b/supabase/migrations/20261007071259_multiplayer_rooms.sql
new file mode 100644
index 0000000..9977230
--- /dev/null
+++ b/supabase/migrations/20261007071259_multiplayer_rooms.sql
@@ -0,0 +1,214 @@
+-- Guest identities are verified by the server's HttpOnly cookie. No client role
+-- can read room secrets, future locations, guesses, or invoke these functions.
+create table public.multiplayer_rooms (
+  id uuid primary key default gen_random_uuid(),
+  revision_id uuid not null references public.revisions(id),
+  host_player_id uuid not null,
+  difficulty text not null check (difficulty in ('easy','normal','hard')),
+  player_limit integer not null check (player_limit between 2 and 16),
+  status text not null default 'lobby' check (status in ('lobby','loading','playing','results','finished','closed')),
+  current_round integer not null default 0 check (current_round between 0 and 4),
+  transition_at timestamptz,
+  created_at timestamptz not null default now()
+);
+create index multiplayer_rooms_revision on public.multiplayer_rooms(revision_id);
+create table public.multiplayer_players (
+  id uuid primary key default gen_random_uuid(),
+  room_id uuid not null references public.multiplayer_rooms(id) on delete cascade,
+  access_hash text not null check (access_hash ~ '^[a-f0-9]{64}$'),
+  display_name text not null check (length(display_name) between 2 and 32 and display_name !~ '[[:cntrl:]]' and display_name !~ U&'[\202A-\202E\2066-\2069]'),
+  ready_round integer not null default -1,
+  has_left boolean not null default false,
+  joined_at timestamptz not null default clock_timestamp(),
+  unique(room_id,access_hash),
+  unique(room_id,id)
+);
+create unique index multiplayer_player_names on public.multiplayer_players(room_id,lower(display_name));
+create table public.multiplayer_rounds (
+  room_id uuid not null references public.multiplayer_rooms(id) on delete cascade,
+  round_number integer not null check (round_number between 0 and 4),
+  viewpoint jsonb not null,
+  deadline timestamptz,
+  closed_at timestamptz,
+  primary key(room_id,round_number)
+);
+create table public.multiplayer_guesses (
+  room_id uuid not null,
+  player_id uuid not null,
+  round_number integer not null,
+  result jsonb not null,
+  primary key(room_id,player_id,round_number),
+  foreign key(room_id,player_id) references public.multiplayer_players(room_id,id) on delete cascade,
+  foreign key(room_id,round_number) references public.multiplayer_rounds(room_id,round_number) on delete cascade
+);
+create index multiplayer_guesses_round on public.multiplayer_guesses(room_id,round_number);
+alter table public.multiplayer_rooms enable row level security;
+alter table public.multiplayer_players enable row level security;
+alter table public.multiplayer_rounds enable row level security;
+alter table public.multiplayer_guesses enable row level security;
+revoke all on public.multiplayer_rooms, public.multiplayer_players, public.multiplayer_rounds, public.multiplayer_guesses from public,anon,authenticated;
+grant all on public.multiplayer_rooms, public.multiplayer_players, public.multiplayer_rounds, public.multiplayer_guesses to service_role;
+
+create function public.create_multiplayer_room(p_dataset uuid,p_difficulty text,p_name text,p_limit integer,p_access_hash text)
+returns uuid language plpgsql security invoker set search_path='' as $$
+declare rid uuid; pid uuid := gen_random_uuid(); rev public.revisions; vp jsonb; n integer := 0;
+begin
+  if p_limit is null or p_limit not between 2 and 16 then raise exception 'Choose between 2 and 16 players'; end if;
+  if p_difficulty is null or p_difficulty not in ('easy','normal','hard') then raise exception 'Invalid difficulty'; end if;
+  select r.* into rev from public.datasets d join public.revisions r on r.id=d.revision_id where d.id=p_dataset and d.state='published';
+  if not found then raise exception 'Map unavailable'; end if;
+  if coalesce(jsonb_array_length(rev.manifest->'viewpoints'),0)<5 then raise exception 'Map has fewer than five viewpoints'; end if;
+  insert into public.multiplayer_rooms(revision_id,host_player_id,difficulty,player_limit) values(rev.id,pid,p_difficulty,p_limit) returning id into rid;
+  insert into public.multiplayer_players(id,room_id,access_hash,display_name) values(pid,rid,p_access_hash,btrim(p_name));
+  for vp in select value from jsonb_array_elements(rev.manifest->'viewpoints') order by random() limit 5 loop
+    insert into public.multiplayer_rounds(room_id,round_number,viewpoint) values(rid,n,vp); n := n+1;
+  end loop;
+  return rid;
+end; $$;
+
+-- One room lock serializes capacity checks, guesses, and deadline transitions.
+-- GET polling also settles disconnected players; it never relies on their timers.
+create function public.multiplayer_tick(p_room uuid)
+returns void language plpgsql security invoker set search_path='' as $$
+declare room public.multiplayer_rooms; turn public.multiplayer_rounds; seconds integer;
+begin
+  select * into room from public.multiplayer_rooms where id=p_room for update;
+  if room.status not in ('finished','closed') and room.created_at < clock_timestamp()-interval '24 hours' then
+    update public.multiplayer_rooms set status='closed',transition_at=null where id=p_room; return;
+  end if;
+  if room.status='results' and room.transition_at<=clock_timestamp() then
+    update public.multiplayer_rooms set current_round=current_round+1,status='loading',transition_at=clock_timestamp()+interval '30 seconds' where id=p_room returning * into room;
+  end if;
+  if room.status='loading' and (
+    room.transition_at<=clock_timestamp() or not exists(select 1 from public.multiplayer_players where room_id=p_room and not has_left and ready_round<>room.current_round)
+  ) then
+    seconds := case room.difficulty when 'easy' then 180 when 'normal' then 90 else 30 end;
+    update public.multiplayer_rounds set deadline=clock_timestamp()+make_interval(secs=>seconds) where room_id=p_room and round_number=room.current_round;
+    update public.multiplayer_rooms set status='playing',transition_at=null where id=p_room returning * into room;
+  end if;
+  if room.status<>'playing' then return; end if;
+  select * into turn from public.multiplayer_rounds where room_id=p_room and round_number=room.current_round;
+  insert into public.multiplayer_guesses(room_id,player_id,round_number,result)
+    select p_room,p.id,room.current_round,jsonb_build_object('score',0,'distance',null,'timedOut',true,'guess',null,'actual',jsonb_build_object('x',turn.viewpoint->'x','z',turn.viewpoint->'z'))
+    from public.multiplayer_players p where p.room_id=p_room and (p.has_left or turn.deadline<=clock_timestamp())
+    on conflict(room_id,player_id,round_number) do nothing;
+  if not exists(select 1 from public.multiplayer_players p where p.room_id=p_room and not exists(
+    select 1 from public.multiplayer_guesses g where g.room_id=p_room and g.player_id=p.id and g.round_number=room.current_round
+  )) then
+    update public.multiplayer_rounds set closed_at=clock_timestamp() where room_id=p_room and round_number=room.current_round;
+    update public.multiplayer_rooms set status=case when current_round=4 then 'finished' else 'results' end,
+      transition_at=case when current_round=4 then null else clock_timestamp()+interval '20 seconds' end where id=p_room;
+  end if;
+end; $$;
+
+-- Only closed rounds contribute scores or reveal locations, even to the host.
+create function public.multiplayer_snapshot(p_room uuid,p_access_hash text)
+returns jsonb language sql security invoker set search_path='' as $$
+  with room as (select * from public.multiplayer_rooms where id=p_room),
+  viewer as (select p.id from public.multiplayer_players p where p.room_id=p_room and p.access_hash=p_access_hash and not p.has_left),
+  totals as (
+    select p.*,coalesce((select sum((g.result->>'score')::integer) from public.multiplayer_guesses g
+      join public.multiplayer_rounds r on r.room_id=g.room_id and r.round_number=g.round_number
+      where g.room_id=p_room and g.player_id=p.id and r.closed_at is not null),0) as total
+    from public.multiplayer_players p where p.room_id=p_room
+  ), ranked as (select *,dense_rank() over(order by total desc) as rank from totals)
+  select jsonb_build_object(
+    'id',room.id,'datasetId',rev.dataset_id,'name',rev.manifest->>'name','difficulty',room.difficulty,
+    'playerLimit',room.player_limit,'playerCount',(select count(*) from totals where not has_left),
+    'status',room.status,'round',room.current_round,'hostId',room.host_player_id,'you',(select id from viewer),
+    'serverNow',floor(extract(epoch from clock_timestamp())*1000),'transitionAt',room.transition_at,
+    'players',case when exists(select 1 from viewer) then coalesce((select jsonb_agg(jsonb_build_object(
+      'id',p.id,'name',p.display_name,'left',p.has_left,'ready',p.ready_round=room.current_round,
+      'submitted',exists(select 1 from public.multiplayer_guesses g where g.room_id=p_room and g.player_id=p.id and g.round_number=room.current_round),
+      'total',p.total,'rank',p.rank
+    ) order by p.rank,p.joined_at,p.id) from ranked p),'[]'::jsonb) else '[]'::jsonb end,
+    'rounds',case when exists(select 1 from viewer) then coalesce((select jsonb_agg(jsonb_build_object(
+      'number',r.round_number,'deadline',r.deadline,'closedAt',r.closed_at,
+      'results',case when r.closed_at is not null then coalesce((select jsonb_agg(g.result||jsonb_build_object('playerId',g.player_id) order by g.player_id)
+        from public.multiplayer_guesses g where g.room_id=p_room and g.round_number=r.round_number),'[]'::jsonb) else '[]'::jsonb end
+    ) order by r.round_number) from public.multiplayer_rounds r where r.room_id=p_room),'[]'::jsonb) else '[]'::jsonb end,
+    'myGuess',case when exists(select 1 from viewer) then (select g.result->'guess' from public.multiplayer_guesses g where g.room_id=p_room and g.player_id=(select id from viewer) and g.round_number=room.current_round) else null end
+  ) from room join public.revisions rev on rev.id=room.revision_id;
+$$;
+
+create function public.multiplayer_action(p_room uuid,p_access_hash text,p_action text,p_payload jsonb default '{}')
+returns jsonb language plpgsql security invoker set search_path='' as $$
+declare room public.multiplayer_rooms; player public.multiplayer_players; turn public.multiplayer_rounds;
+  target uuid; n integer; px double precision; pz double precision; distance double precision;
+  diagonal double precision; points integer; bounds jsonb; answer jsonb; active integer;
+begin
+  select * into room from public.multiplayer_rooms where id=p_room for update;
+  if not found then raise exception 'Room not found'; end if;
+  select * into player from public.multiplayer_players where room_id=p_room and access_hash=p_access_hash;
+  if p_action='join' then
+    if room.status='closed' then raise exception 'This room is closed'; end if;
+    if player.id is not null and not player.has_left then return public.multiplayer_snapshot(p_room,p_access_hash); end if;
+    if room.status<>'lobby' then raise exception 'This match has already started'; end if;
+    select count(*) into active from public.multiplayer_players where room_id=p_room and not has_left;
+    if active>=room.player_limit then raise exception 'This room is full'; end if;
+    if exists(select 1 from public.multiplayer_players where room_id=p_room and lower(display_name)=lower(btrim(p_payload->>'name'))) then
+      raise exception 'This name is already taken in this room';
+    end if;
+    insert into public.multiplayer_players(room_id,access_hash,display_name) values(p_room,p_access_hash,btrim(p_payload->>'name'));
+    return public.multiplayer_snapshot(p_room,p_access_hash);
+  end if;
+  if player.id is null or player.has_left then
+    if p_action='view' then return public.multiplayer_snapshot(p_room,p_access_hash); end if;
+    raise exception 'Room membership permission required';
+  end if;
+  perform public.multiplayer_tick(p_room);
+  select * into room from public.multiplayer_rooms where id=p_room;
+  if p_action in ('start','next','kick','close') and room.host_player_id<>player.id then raise exception 'Room owner permission required'; end if;
+  if p_action='start' then
+    if room.status<>'lobby' then return public.multiplayer_snapshot(p_room,p_access_hash); end if;
+    if (select count(*) from public.multiplayer_players where room_id=p_room and not has_left)<2 then raise exception 'Invite at least one friend before starting'; end if;
+    update public.multiplayer_rooms set status='loading',transition_at=clock_timestamp()+interval '30 seconds' where id=p_room;
+  elsif p_action='ready' then
+    n := (p_payload->>'round')::integer;
+    if room.status='loading' and n=room.current_round then update public.multiplayer_players set ready_round=n where id=player.id; end if;
+  elsif p_action='guess' then
+    n := (p_payload->>'round')::integer;
+    if exists(select 1 from public.multiplayer_guesses where room_id=p_room and player_id=player.id and round_number=n) then
+      return public.multiplayer_snapshot(p_room,p_access_hash);
+    end if;
+    if room.status<>'playing' or n is distinct from room.current_round then raise exception 'Round is not active'; end if;
+    select * into turn from public.multiplayer_rounds where room_id=p_room and round_number=n;
+    px := (p_payload->>'x')::double precision; pz := (p_payload->>'z')::double precision;
+    if px is null or pz is null then raise exception 'Place a guess first'; end if;
+    select manifest->'bounds' into bounds from public.revisions where id=room.revision_id;
+    if px='NaN'::float8 or pz='NaN'::float8 or px<(bounds->>'minX')::float8 or px>(bounds->>'maxX')::float8 or pz<(bounds->>'minZ')::float8 or pz>(bounds->>'maxZ')::float8 then raise exception 'Guess outside map'; end if;
+    -- Check again after validation: a request arriving at the deadline scores zero.
+    if turn.deadline<=clock_timestamp() then
+      perform public.multiplayer_tick(p_room); return public.multiplayer_snapshot(p_room,p_access_hash);
+    end if;
+    distance := sqrt(power(px-(turn.viewpoint->>'x')::float8,2)+power(pz-(turn.viewpoint->>'z')::float8,2));
+    diagonal := sqrt(power((bounds->>'maxX')::float8-(bounds->>'minX')::float8,2)+power((bounds->>'maxZ')::float8-(bounds->>'minZ')::float8,2));
+    points := case when distance<=1 then 5000 else round(5000*exp(-5*distance/diagonal))::integer end;
+    answer := jsonb_build_object('score',points,'distance',distance,'timedOut',false,'guess',jsonb_build_object('x',px,'z',pz),'actual',jsonb_build_object('x',turn.viewpoint->'x','z',turn.viewpoint->'z'));
+    insert into public.multiplayer_guesses(room_id,player_id,round_number,result) values(p_room,player.id,n,answer);
+  elsif p_action='next' then
+    n := (p_payload->>'round')::integer;
+    if n<room.current_round then return public.multiplayer_snapshot(p_room,p_access_hash); end if;
+    if room.status<>'results' or n is distinct from room.current_round then raise exception 'Wait for the round to finish'; end if;
+    update public.multiplayer_rooms set current_round=current_round+1,status='loading',transition_at=clock_timestamp()+interval '30 seconds' where id=p_room;
+  elsif p_action='kick' then
+    if room.status<>'lobby' then raise exception 'Players can only be removed before the match starts'; end if;
+    target := (p_payload->>'playerId')::uuid;
+    if target=room.host_player_id then raise exception 'The owner cannot remove themselves'; end if;
+    delete from public.multiplayer_players where room_id=p_room and id=target;
+  elsif p_action='leave' then
+    if room.status='lobby' then delete from public.multiplayer_players where id=player.id;
+    else update public.multiplayer_players set has_left=true where id=player.id; end if;
+    select id into target from public.multiplayer_players where room_id=p_room and not has_left order by joined_at,id limit 1;
+    if target is null then update public.multiplayer_rooms set status='closed',transition_at=null where id=p_room;
+    elsif room.host_player_id=player.id then update public.multiplayer_rooms set host_player_id=target where id=p_room; end if;
+  elsif p_action='close' then
+    update public.multiplayer_rooms set status='closed',transition_at=null where id=p_room;
+  elsif p_action<>'view' then raise exception 'Invalid room action';
+  end if;
+  perform public.multiplayer_tick(p_room);
+  return public.multiplayer_snapshot(p_room,p_access_hash);
+end; $$;
+
+revoke all on function public.create_multiplayer_room(uuid,text,text,integer,text),public.multiplayer_tick(uuid),public.multiplayer_snapshot(uuid,text),public.multiplayer_action(uuid,text,text,jsonb) from public,anon,authenticated;
+grant execute on function public.create_multiplayer_room(uuid,text,text,integer,text),public.multiplayer_tick(uuid),public.multiplayer_snapshot(uuid,text),public.multiplayer_action(uuid,text,text,jsonb) to service_role;
diff --git a/tests/multiplayer.test.ts b/tests/multiplayer.test.ts
new file mode 100644
index 0000000..bde8fe2
--- /dev/null
+++ b/tests/multiplayer.test.ts
@@ -0,0 +1,46 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import {
+  createRoomSchema,
+  joinRoomSchema,
+  roomGuessSchema,
+} from "../shared/multiplayer";
+
+const map = "00000000-0000-4000-8000-000000000000";
+test("room limits include the owner and stay between 2 and 16", () => {
+  for (const playerLimit of [2, 16])
+    assert.equal(
+      createRoomSchema.parse({
+        datasetId: map,
+        difficulty: "normal",
+        displayName: " Alex ",
+        playerLimit,
+      }).displayName,
+      "Alex",
+    );
+  for (const playerLimit of [1, 17, 2.5, "16", null])
+    assert.equal(
+      createRoomSchema.safeParse({
+        datasetId: map,
+        difficulty: "normal",
+        displayName: "Alex",
+        playerLimit,
+      }).success,
+      false,
+    );
+});
+test("multiplayer names and guesses reject hidden controls, invalid rounds, and non-finite positions", () => {
+  assert.equal(
+    joinRoomSchema.parse({ displayName: " Друг " }).displayName,
+    "Друг",
+  );
+  for (const displayName of ["a", "x\nname", "name\u202e", "a".repeat(33)])
+    assert.equal(joinRoomSchema.safeParse({ displayName }).success, false);
+  for (const payload of [
+    { round: 5, x: 0, z: 0 },
+    { round: 0, x: Infinity, z: 0 },
+    { round: 0, x: NaN, z: 0 },
+    { round: 0, x: 0 },
+  ])
+    assert.equal(roomGuessSchema.safeParse(payload).success, false);
+});