fix(browser): Skip browserTracingIntegration setup for bot user agents

.size-limit.js

@@ -82,7 +82,7 @@ module.exports = [
     path: 'packages/browser/build/npm/esm/prod/index.js',
     import: createImport('init', 'browserTracingIntegration', 'replayIntegration', 'replayCanvasIntegration'),
     gzip: true,
-    limit: '86 KB',
+    limit: '87 KB',
   },
   {
     name: '@sentry/browser (incl. Tracing, Replay, Feedback)',
@@ -255,7 +255,7 @@ module.exports = [
     path: createCDNPath('bundle.tracing.logs.metrics.min.js'),
     gzip: false,
     brotli: false,
-    limit: '131 KB',
+    limit: '132 KB',
   },
   {
     name: 'CDN Bundle (incl. Replay, Logs, Metrics) - uncompressed',
@@ -269,7 +269,7 @@ module.exports = [
     path: createCDNPath('bundle.tracing.replay.min.js'),
     gzip: false,
     brotli: false,
-    limit: '245 KB',
+    limit: '246 KB',
   },
   {
     name: 'CDN Bundle (incl. Tracing, Replay, Logs, Metrics) - uncompressed',
@@ -308,7 +308,7 @@ module.exports = [
     import: createImport('init'),
     ignore: ['$app/stores'],
     gzip: true,
-    limit: '43 KB',
+    limit: '44 KB',
   },
   // Node-Core SDK (ESM)
   {

packages/browser/src/tracing/browserTracingIntegration.ts

@@ -54,6 +54,22 @@ import { defaultRequestInstrumentationOptions, instrumentOutgoingRequests } from
 
 export const BROWSER_TRACING_INTEGRATION_ID = 'BrowserTracing';
 
+/**
+ * We don't want to start a bunch of idle timers and PerformanceObservers
+ * for web crawlers, as they may prevent the page from being seen as "idle"
+ * by the crawler's rendering engine (e.g. Googlebot's headless Chromium).
+ */
+const BOT_USER_AGENT_RE =
+  /Googlebot|Google-InspectionTool|Storebot-Google|Bingbot|Slurp|DuckDuckBot|Baiduspider|YandexBot|Facebot|facebookexternalhit|LinkedInBot|Twitterbot|Applebot/i;
+
+function _isBotUserAgent(): boolean {
+  const nav = WINDOW.navigator as Navigator | undefined;
+  if (!nav?.userAgent) {
+    return false;
+  }
+  return BOT_USER_AGENT_RE.test(nav.userAgent);
+}
+
 interface RouteInfo {
   name: string | undefined;
   source: TransactionSource | undefined;
@@ -384,6 +400,8 @@ export const browserTracingIntegration = ((options: Partial<BrowserTracingOption
     ...options,
   };
 
+  const _isBot = _isBotUserAgent();
+
   let _collectWebVitals: undefined | (() => void);
   let lastInteractionTimestamp: number | undefined;
 
@@ -484,6 +502,11 @@ export const browserTracingIntegration = ((options: Partial<BrowserTracingOption
   return {
     name: BROWSER_TRACING_INTEGRATION_ID,
     setup(client) {
+      if (_isBot) {
+        DEBUG_BUILD && debug.log('[Tracing] Skipping browserTracingIntegration setup for bot user agent.');
+        return;
+      }
+
       registerSpanErrorInstrumentation();
 
       _collectWebVitals = startTrackingWebVitals({
@@ -630,6 +653,10 @@ export const browserTracingIntegration = ((options: Partial<BrowserTracingOption
     },
 
     afterAllSetup(client) {
+      if (_isBot) {
+        return;
+      }
+
       let startingUrl: string | undefined = getLocationHref();
 
       if (linkPreviousTrace !== 'off') {

packages/browser/test/tracing/browserTracingIntegration.test.ts

@@ -86,6 +86,68 @@ describe('browserTracingIntegration', () => {
     Object.defineProperty(WINDOW, 'history', { value: originalGlobalHistory });
   });
 
+  describe('bot user agent detection', () => {
+    let originalNavigator: Navigator;
+
+    beforeEach(() => {
+      originalNavigator = WINDOW.navigator;
+    });
+
+    afterEach(() => {
+      Object.defineProperty(WINDOW, 'navigator', { value: originalNavigator, writable: true, configurable: true });
+    });
+
+    function setUserAgent(ua: string): void {
+      Object.defineProperty(WINDOW, 'navigator', {
+        value: { userAgent: ua },
+        writable: true,
+        configurable: true,
+      });
+    }
+
+    it.each([
+      'Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)',
+      'Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/W.X.Y.Z Mobile Safari/537.36 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)',
+      'Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; Bingbot/2.0; +http://www.bing.com/bingbot.htm) Chrome/W.X.Y.Z Safari/537.36',
+      'Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)',
+      'facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)',
+      'LinkedInBot/1.0 (compatible; Mozilla/5.0)',
+      'Twitterbot/1.0',
+      'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_5) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1.1 Safari/605.1.15 (Applebot/0.1)',
+      'Mozilla/5.0 (compatible; Google-InspectionTool/1.0)',
+    ])('skips tracing setup for bot user agent: %s', ua => {
+      setUserAgent(ua);
+
+      const client = new BrowserClient(
+        getDefaultBrowserClientOptions({
+          tracesSampleRate: 1,
+          integrations: [browserTracingIntegration()],
+        }),
+      );
+      setCurrentClient(client);
+      client.init();
+
+      expect(getActiveSpan()).toBeUndefined();
+    });
+
+    it('does not skip tracing setup for normal user agents', () => {
+      setUserAgent(
+        'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36',
+      );
+
+      const client = new BrowserClient(
+        getDefaultBrowserClientOptions({
+          tracesSampleRate: 1,
+          integrations: [browserTracingIntegration()],
+        }),
+      );
+      setCurrentClient(client);
+      client.init();
+
+      expect(getActiveSpan()).toBeDefined();
+    });
+  });
+
   it('works with tracing enabled', () => {
     const client = new BrowserClient(
       getDefaultBrowserClientOptions({

packages/nextjs/test/config/conflictingDebugOptions.test.ts

@@ -20,7 +20,15 @@ describe('debug: true + removeDebugLogging warning', () => {
   let originalLocation: unknown;
   let originalAddEventListener: unknown;
 
-  beforeAll(() => {
+  beforeAll(async () => {
+    // Pre-warm V8 compilation cache for the large SDK module graphs.
+    // Without this, the first dynamic import after vi.resetModules() can hang
+    // because vitest needs to compile the entire module graph from scratch.
+    await import('../../src/client/index.js');
+    await import('../../src/server/index.js');
+    await import('../../src/edge/index.js');
+    vi.resetModules();
+
     dom = new JSDOM('<!doctype html><html><head></head><body></body></html>', { url: 'https://example.com/' });
 
     originalDocument = (globalThis as any).document;