getsentry · logaretm · Mar 16, 2026 · Mar 16, 2026 · Mar 16, 2026 · Mar 23, 2026
diff --git a/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/init.js b/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/init.js
@@ -0,0 +1,11 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+window._testBaseTimestamp = performance.timeOrigin / 1000;
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  integrations: [Sentry.browserTracingIntegration({ idleTimeout: 9000 }), Sentry.spanStreamingIntegration()],
+  traceLifecycle: 'stream',
+  tracesSampleRate: 1,
+});
diff --git a/...browser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/subject.js b/...browser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/subject.js
@@ -0,0 +1,17 @@
+import { simulateCLS } from '../../../../utils/web-vitals/cls.ts';
+
+// Simulate Layout shift right at the beginning of the page load, depending on the URL hash
+// don't run if expected CLS is NaN
+const expectedCLS = Number(location.hash.slice(1));
+if (expectedCLS && expectedCLS >= 0) {
+  simulateCLS(expectedCLS).then(() => window.dispatchEvent(new Event('cls-done')));
+}
+
+// Simulate layout shift whenever the trigger-cls event is dispatched
+// Cannot trigger via a button click because expected layout shift after
+// an interaction doesn't contribute to CLS.
+window.addEventListener('trigger-cls', () => {
+  simulateCLS(0.1).then(() => {
+    window.dispatchEvent(new Event('cls-done'));
+  });
+});
diff --git a/...wser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/template.html b/...wser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/template.html
@@ -0,0 +1,10 @@
+<!doctype html>
+<html>
+  <head>
+    <meta charset="utf-8" />
+  </head>
+  <body>
+    <div id="content"></div>
+    <p>Some content</p>
+  </body>
+</html>
diff --git a/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/test.ts b/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-cls-streamed-spans/test.ts
@@ -0,0 +1,77 @@
+import type { Page } from '@playwright/test';
+import { expect } from '@playwright/test';
+import { sentryTest } from '../../../../utils/fixtures';
+import { shouldSkipTracingTest, testingCdnBundle } from '../../../../utils/helpers';
+import { getSpanOp, waitForStreamedSpan } from '../../../../utils/spanUtils';
+
+sentryTest.beforeEach(async ({ browserName, page }) => {
+  if (shouldSkipTracingTest() || testingCdnBundle() || browserName !== 'chromium') {
+    sentryTest.skip();
+  }
+
+  await page.setViewportSize({ width: 800, height: 1200 });
+});
+
+function waitForLayoutShift(page: Page): Promise<void> {
+  return page.evaluate(() => {
+    return new Promise(resolve => {
+      window.addEventListener('cls-done', () => resolve());
+    });
+  });
+}
+
+function hidePage(page: Page): Promise<void> {
+  return page.evaluate(() => {
+    window.dispatchEvent(new Event('pagehide'));
+  });
+}
+
+sentryTest('captures CLS as a streamed span with source attributes', async ({ getLocalTestUrl, page }) => {
+  const url = await getLocalTestUrl({ testDir: __dirname });
+
+  const clsSpanPromise = waitForStreamedSpan(page, span => getSpanOp(span) === 'ui.webvital.cls');
+
+  await page.goto(`${url}#0.15`);
+  await waitForLayoutShift(page);
+  await hidePage(page);
+
+  const clsSpan = await clsSpanPromise;
+
+  expect(clsSpan.attributes?.['sentry.op']).toEqual({ type: 'string', value: 'ui.webvital.cls' });
+  expect(clsSpan.attributes?.['sentry.origin']).toEqual({ type: 'string', value: 'auto.http.browser.cls' });
+  expect(clsSpan.attributes?.['sentry.exclusive_time']).toEqual({ type: 'integer', value: 0 });
+  expect(clsSpan.attributes?.['user_agent.original']?.value).toEqual(expect.stringContaining('Chrome'));
+
+  // Check browser.web_vital.cls.source attributes
+  expect(clsSpan.attributes?.['browser.web_vital.cls.source.1']?.value).toEqual(
+    expect.stringContaining('body > div#content > p'),
+  );
+
+  // Check pageload span id is present
+  expect(clsSpan.attributes?.['sentry.pageload.span_id']?.value).toMatch(/[\da-f]{16}/);
+
+  // CLS is a point-in-time metric
+  expect(clsSpan.start_timestamp).toEqual(clsSpan.end_timestamp);
+
+  expect(clsSpan.span_id).toMatch(/^[\da-f]{16}$/);
+  expect(clsSpan.trace_id).toMatch(/^[\da-f]{32}$/);
+});
+
+sentryTest('CLS streamed span has web vital value attribute', async ({ getLocalTestUrl, page }) => {
+  const url = await getLocalTestUrl({ testDir: __dirname });
+
+  const clsSpanPromise = waitForStreamedSpan(page, span => getSpanOp(span) === 'ui.webvital.cls');
+
+  await page.goto(`${url}#0.1`);
+  await waitForLayoutShift(page);
+  await hidePage(page);
+
+  const clsSpan = await clsSpanPromise;
+
+  // The CLS value should be set as a browser.web_vital.cls.value attribute
+  expect(clsSpan.attributes?.['browser.web_vital.cls.value']?.type).toBe('double');
+  // Flakey value dependent on timings -> we check for a range
+  const clsValue = clsSpan.attributes?.['browser.web_vital.cls.value']?.value as number;
+  expect(clsValue).toBeGreaterThan(0.05);
+  expect(clsValue).toBeLessThan(0.15);
+});
diff --git a/...es/tracing/metrics/web-vitals-lcp-streamed-spans/assets/sentry-logo-600x179.png b/...es/tracing/metrics/web-vitals-lcp-streamed-spans/assets/sentry-logo-600x179.png
diff --git a/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-lcp-streamed-spans/init.js b/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-lcp-streamed-spans/init.js
@@ -0,0 +1,11 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+window._testBaseTimestamp = performance.timeOrigin / 1000;
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  integrations: [Sentry.browserTracingIntegration({ idleTimeout: 9000 }), Sentry.spanStreamingIntegration()],
+  traceLifecycle: 'stream',
+  tracesSampleRate: 1,
+});
diff --git a/...wser-integration-tests/suites/tracing/metrics/web-vitals-lcp-streamed-spans/template.html b/...wser-integration-tests/suites/tracing/metrics/web-vitals-lcp-streamed-spans/template.html
@@ -0,0 +1,10 @@
+<!doctype html>
+<html>
+  <head>
+    <meta charset="utf-8" />
+  </head>
+  <body>
+    <div id="content"></div>
+    <img src="https://sentry-test-site.example/my/image.png" />
+  </body>
+</html>
diff --git a/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-lcp-streamed-spans/test.ts b/...es/browser-integration-tests/suites/tracing/metrics/web-vitals-lcp-streamed-spans/test.ts
@@ -0,0 +1,66 @@
+import type { Page, Route } from '@playwright/test';
+import { expect } from '@playwright/test';
+import { sentryTest } from '../../../../utils/fixtures';
+import { shouldSkipTracingTest, testingCdnBundle } from '../../../../utils/helpers';
+import { getSpanOp, waitForStreamedSpan } from '../../../../utils/spanUtils';
+
+sentryTest.beforeEach(async ({ browserName, page }) => {
+  if (shouldSkipTracingTest() || testingCdnBundle() || browserName !== 'chromium') {
+    sentryTest.skip();
+  }
+
+  await page.setViewportSize({ width: 800, height: 1200 });
+});
+
+function hidePage(page: Page): Promise<void> {
+  return page.evaluate(() => {
+    window.dispatchEvent(new Event('pagehide'));
+  });
+}
+
+sentryTest('captures LCP as a streamed span with element attributes', async ({ getLocalTestUrl, page }) => {
+  page.route('**', route => route.continue());
+  page.route('**/my/image.png', async (route: Route) => {
+    return route.fulfill({
+      path: `${__dirname}/assets/sentry-logo-600x179.png`,
+    });
+  });
+
+  const url = await getLocalTestUrl({ testDir: __dirname });
+
+  const lcpSpanPromise = waitForStreamedSpan(page, span => getSpanOp(span) === 'ui.webvital.lcp');
+
+  await page.goto(url);
+
+  // Wait for LCP to be captured
+  await page.waitForTimeout(1000);
+
+  await hidePage(page);
+
+  const lcpSpan = await lcpSpanPromise;
+
+  expect(lcpSpan.attributes?.['sentry.op']).toEqual({ type: 'string', value: 'ui.webvital.lcp' });
+  expect(lcpSpan.attributes?.['sentry.origin']).toEqual({ type: 'string', value: 'auto.http.browser.lcp' });
+  expect(lcpSpan.attributes?.['sentry.exclusive_time']).toEqual({ type: 'integer', value: 0 });
+  expect(lcpSpan.attributes?.['user_agent.original']?.value).toEqual(expect.stringContaining('Chrome'));
+
+  // Check browser.web_vital.lcp.* attributes
+  expect(lcpSpan.attributes?.['browser.web_vital.lcp.element']?.value).toEqual(expect.stringContaining('body > img'));
+  expect(lcpSpan.attributes?.['browser.web_vital.lcp.url']?.value).toBe(
+    'https://sentry-test-site.example/my/image.png',
+  );
+  expect(lcpSpan.attributes?.['browser.web_vital.lcp.size']?.value).toEqual(expect.any(Number));
+
+  // Check web vital value attribute
+  expect(lcpSpan.attributes?.['browser.web_vital.lcp.value']?.type).toBe('double');
+  expect(lcpSpan.attributes?.['browser.web_vital.lcp.value']?.value).toBeGreaterThan(0);
+
+  // Check pageload span id is present
+  expect(lcpSpan.attributes?.['sentry.pageload.span_id']?.value).toMatch(/[\da-f]{16}/);
+
+  // Span should have meaningful duration (navigation start -> LCP event)
+  expect(lcpSpan.end_timestamp).toBeGreaterThan(lcpSpan.start_timestamp);
+
+  expect(lcpSpan.span_id).toMatch(/^[\da-f]{16}$/);
+  expect(lcpSpan.trace_id).toMatch(/^[\da-f]{32}$/);
+});
diff --git a/packages/browser-utils/src/index.ts b/packages/browser-utils/src/index.ts
@@ -20,6 +20,8 @@ export { startTrackingElementTiming } from './metrics/elementTiming';
 
 export { extractNetworkProtocol } from './metrics/utils';
 
+export { trackClsAsSpan, trackInpAsSpan, trackLcpAsSpan } from './metrics/webVitalSpans';
+
 export { addClickKeypressInstrumentationHandler } from './instrument/dom';
 
 export { addHistoryInstrumentationHandler } from './instrument/history';

diff --git a/packages/browser-utils/src/metrics/browserMetrics.ts b/packages/browser-utils/src/metrics/browserMetrics.ts
@@ -75,8 +75,18 @@ let _lcpEntry: LargestContentfulPaint | undefined;
 let _clsEntry: LayoutShift | undefined;
 
 interface StartTrackingWebVitalsOptions {
-  recordClsStandaloneSpans: boolean;
-  recordLcpStandaloneSpans: boolean;
+  /**
+   * When `true`, CLS is tracked as a standalone span. When `false`, CLS is
+   * recorded as a measurement on the pageload span. When `undefined`, CLS
+   * tracking is skipped entirely (e.g. because span streaming handles it).
+   */
+  recordClsStandaloneSpans: boolean | undefined;
+  /**
+   * When `true`, LCP is tracked as a standalone span. When `false`, LCP is
+   * recorded as a measurement on the pageload span. When `undefined`, LCP
+   * tracking is skipped entirely (e.g. because span streaming handles it).
+   */
+  recordLcpStandaloneSpans: boolean | undefined;
   client: Client;
 }
 
@@ -97,9 +107,22 @@ export function startTrackingWebVitals({
     if (performance.mark) {
       WINDOW.performance.mark('sentry-tracing-init');
     }
-    const lcpCleanupCallback = recordLcpStandaloneSpans ? trackLcpAsStandaloneSpan(client) : _trackLCP();
+
+    const lcpCleanupCallback =
+      recordLcpStandaloneSpans === true
+        ? trackLcpAsStandaloneSpan(client)
+        : recordLcpStandaloneSpans === false
+          ? _trackLCP()
+          : undefined;
+
+    const clsCleanupCallback =
+      recordClsStandaloneSpans === true
+        ? trackClsAsStandaloneSpan(client)
+        : recordClsStandaloneSpans === false
+          ? _trackCLS()
+          : undefined;
+
     const ttfbCleanupCallback = _trackTtfb();
-    const clsCleanupCallback = recordClsStandaloneSpans ? trackClsAsStandaloneSpan(client) : _trackCLS();
 
     return (): void => {
       lcpCleanupCallback?.();

diff --git a/packages/browser-utils/src/metrics/inp.ts b/packages/browser-utils/src/metrics/inp.ts
@@ -37,7 +37,7 @@ const ELEMENT_NAME_TIMESTAMP_MAP = new Map<number, string>();
  * 60 seconds is the maximum for a plausible INP value
  * (source: Me)
  */
-const MAX_PLAUSIBLE_INP_DURATION = 60;
+export const MAX_PLAUSIBLE_INP_DURATION = 60;
 /**
  * Start tracking INP webvital events.
  */
@@ -54,7 +54,7 @@ export function startTrackingINP(): () => void {
   return () => undefined;
 }
 
-const INP_ENTRY_MAP: Record<string, 'click' | 'hover' | 'drag' | 'press'> = {
+export const INP_ENTRY_MAP: Record<string, 'click' | 'hover' | 'drag' | 'press'> = {
   click: 'click',
   pointerdown: 'click',
   pointerup: 'click',

diff --git a/packages/browser-utils/src/metrics/instrument.ts b/packages/browser-utils/src/metrics/instrument.ts
@@ -114,7 +114,6 @@ let _previousCls: Metric | undefined;
 let _previousLcp: Metric | undefined;
 let _previousTtfb: Metric | undefined;
 let _previousInp: Metric | undefined;
-
 /**
  * Add a callback that will be triggered when a CLS metric is available.
  * Returns a cleanup callback which can be called to remove the instrumentation handler.