diff --git a/packages/server/src/index.ts b/packages/server/src/index.ts
index 148fb15..cabaa9c 100644
--- a/packages/server/src/index.ts
+++ b/packages/server/src/index.ts
@@ -113,6 +113,46 @@ const roomsPerAddress = new SlidingLimit(12, 60 * 60 * 1000);
 /** Screenshots for the desk: a few per address per hour, like reports. */
 const imagesPerAddress = new SlidingLimit(6, 60 * 60 * 1000);
 const IMAGE_MAX_BYTES = 2_500_000;
+/** Crash reports from browsers: a crashing tab reloads and crashes again, so a few per address per hour say all there is. */
+const crashReportsPerAddress = new SlidingLimit(10, 60 * 60 * 1000);
+const CRASH_REPORT_MAX_BYTES = 64 * 1024;
+
+/** Chromium sends the Reporting API's crash reports here, after the fact,
+ * from the browser itself: a tab that crashes takes the page's own error
+ * reporting down with it. Each crash is logged and filed in Sentry as a
+ * warning, which rings no bell. Other report types are ignored. */
+function receiveBrowserReports(req: IncomingMessage, res: ServerResponse): void {
+  const address = clientAddress(req.headers, req.socket.remoteAddress);
+  let raw = "";
+  let tooBig = false;
+  req.setEncoding("utf8");
+  req.on("data", (chunk: string) => {
+    if (tooBig) return;
+    raw += chunk;
+    if (raw.length > CRASH_REPORT_MAX_BYTES) tooBig = true;
+  });
+  req.on("end", () => {
+    res.writeHead(204).end();
+    if (tooBig) return;
+    let reports: unknown;
+    try { reports = JSON.parse(raw); } catch { return; }
+    if (!Array.isArray(reports)) return;
+    for (const r of reports as { type?: unknown; url?: unknown; user_agent?: unknown; body?: Record<string, unknown> }[]) {
+      if (r?.type !== "crash" || !crashReportsPerAddress.allow(address)) continue;
+      const url = String(r.url ?? "").slice(0, 200);
+      const room = url.match(/\/join\/([A-Za-z0-9]{4})/)?.[1]?.toUpperCase() ?? "none";
+      const reason = typeof r.body?.reason === "string" ? r.body.reason.slice(0, 40) : "unknown";
+      const userAgent = String(r.user_agent ?? "").slice(0, 300);
+      console.warn(`browser tab crashed: room ${room}, reason ${reason}, ${userAgent}`);
+      Sentry.captureMessage("A player's browser tab crashed", {
+        level: "warning",
+        fingerprint: ["browser-crash", reason],
+        tags: { room, reason },
+        extra: { url, userAgent, body: r.body ?? null },
+      });
+    }
+  });
+}
 
 /** A picture for a report, POSTed right after the report is filed: one
  * per report, within the hour, PNG/JPEG/WebP by its own first bytes, kept
@@ -372,6 +412,7 @@ const httpServer = createServer((req, res) => {
     if (req.method === "POST") {
       const picture = (req.url ?? "").split("?")[0]!.match(/^\/api\/feedback-image\/([0-9a-f]{8})$/);
       if (picture) { receiveFeedbackImage(req, res, picture[1]!); return; }
+      if ((req.url ?? "").split("?")[0] === "/api/reports") { receiveBrowserReports(req, res); return; }
       res.writeHead(404).end();
       return;
     }
@@ -380,6 +421,8 @@ const httpServer = createServer((req, res) => {
       return;
     }
     res.setHeader("x-content-type-options", "nosniff");
+    // Where Chromium sends a crash report about a tab that showed this page.
+    res.setHeader("reporting-endpoints", `default="${requestBase(req)}/api/reports"`);
     if (!staticRoot) {
       res.writeHead(404).end("client not built");
       return;
diff --git a/packages/web/src/main.ts b/packages/web/src/main.ts
index 3dfcd00..aa863a2 100644
--- a/packages/web/src/main.ts
+++ b/packages/web/src/main.ts
@@ -10,7 +10,8 @@ if (import.meta.env.VITE_SENTRY_DSN) {
     environment: "production",
     // Facebook's in-app browser injects its own scripts (iabjs://) and
     // reports their failures as ours when the page unloads.
-    denyUrls: [/^iabjs:\/\//],
+    // Extensions run their own scripts in the page, and their failures are not ours.
+    denyUrls: [/^iabjs:\/\//, /^(chrome|moz|safari(-web)?)-extension:\/\//],
     ignoreErrors: ["Java object is gone"],
   });
 }
diff --git a/packages/web/src/net.svelte.ts b/packages/web/src/net.svelte.ts
index b492139..ced9c7f 100644
--- a/packages/web/src/net.svelte.ts
+++ b/packages/web/src/net.svelte.ts
@@ -4,6 +4,7 @@ import type { ReplayStep } from "./catchup";
 import type { Command, GameEvent, GameView, Side } from "@wizwar/engine";
 import { cardDef, isPermanentDuration } from "@wizwar/engine";
 import { receiptFor } from "./receipt";
+import * as Sentry from "@sentry/browser";
 
 /** The same server over plain HTTP, for the one door a socket cannot carry: a picture. */
 const API_URL =
@@ -572,6 +573,8 @@ class Net {
         break;
       case "room":
         this.roomId = msg.roomId;
+        // An error report names the table it happened at, and from which seat.
+        Sentry.setTags({ room: msg.roomId, seat: this.spectating ? "gallery" : (this.you ?? "none") });
         this.roomColors = msg.colors ?? {};
         this.roomBots = msg.bots ?? {};
         this.standIns = msg.standIns ?? [];
@@ -1001,6 +1004,7 @@ class Net {
    * line, and wiping it would erase the only notice of why. */
   leaveLocal(): void {
     localStorage.removeItem(SEAT_KEY);
+    Sentry.setTags({ room: "none", seat: "none" });
     this.missedSteps = null;
     this.catchUp = null;
     this.pending = null;