Performance Profile

How It Works

cursor-ide-browser

browser_profile_start

browser_profile_stop

~/.cursor/browser-logs/

Steps

1. Ensure the app is running — start the dev server if it isn't already running.
2. Navigate to the slow page:

   Tool: browser_navigate
   Arguments: { "url": "http://localhost:3000/slow-page" }

3. Start profiling:

   Tool: browser_profile_start

4. Reproduce the slow interaction — use browser tools to trigger the slow behavior:
   • Click buttons, scroll, type in inputs, navigate between pages
   • Use

     browser_click

     ,

     browser_scroll

     ,

     browser_fill

     to interact
   • Wait a few seconds for the interaction to complete
5. Stop profiling:

   Tool: browser_profile_stop

   This writes two files to

   ~/.cursor/browser-logs/

   :

   • cpu-profile-{timestamp}.json

     — raw Chrome DevTools profile

   • cpu-profile-{timestamp}-summary.md

     — human-readable summary
6. Analyze the results — read both files. Key things to look for in the raw JSON:

   • profile.nodes[].hitCount

     — how many samples hit each function

   • profile.nodes[].callFrame.functionName

     — the function names

   • profile.samples.length

     — total number of samples collected
   Cross-reference with the summary to identify:
   • Functions consuming the most CPU time
   • Unexpected re-renders or layout thrashing
   • Expensive third-party library calls
   • Synchronous operations blocking the main thread
7. Suggest fixes — based on the profile data, recommend specific optimizations:
   • Memoize expensive computations
   • Debounce rapid event handlers
   • Move heavy work to a Web Worker
   • Lazy-load components or routes
   • Virtualize long lists

Notes

• Always read the raw

  .json

  profile to verify the summary — the summary can miss nuances.
• Profile in development mode first, but be aware that React dev mode adds overhead. For accurate measurements, profile a production build.
• Short profiles (2-5 seconds of interaction) are usually more useful than long ones.
• Compare before/after profiles to verify your optimization actually helped.