browser_perf_metrics
Get Core Web Vitals and performance metrics for the current page.
Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
sessionId | string | Yes | Session ID from browser_navigate |
Example
Check the performance metrics and Web Vitals for this pageResponse
Returns a comprehensive performance report:
Core Web Vitals
| Metric | Description | Good Threshold |
|---|---|---|
| TTFB | Time to First Byte | < 800ms |
| FCP | First Contentful Paint | < 1.8s |
| LCP | Largest Contentful Paint | < 2.5s |
| CLS | Cumulative Layout Shift | < 0.1 |
Page Load
- DOM Content Loaded — when HTML is fully parsed
- Full Load — when all resources are loaded
Page Size
- DOM Nodes — total elements in the DOM
- Resources — total network requests
- Transfer Size — total bytes transferred
Resources by Type
Breakdown of requests by type: scripts, stylesheets, images, fonts, fetch/XHR, etc.
Notes
- Navigate to a page first with
browser_navigate, then call this tool - Metrics are captured from the browser's Performance API
- CLS may increase over time as the page loads — check after full load