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How to use Lighthouse Compare

This guide shows how to export Lighthouse reports as JSON and compare before vs after runs in this app.

Back to compare

1) Generate a Lighthouse report

  1. Open your page in Chrome.
  2. Open DevTools (`F12` or `Cmd/Ctrl + Shift + I`).
  3. Go to the Lighthouse tab.
  4. Select the device type you want to test (`Desktop` or `Mobile`).
  5. Run the audit and wait for the report to finish.

2) Save the report as JSON

In the report screen, open the 3-dot menu at the top-right and clickSave as JSON (same action shown in your screenshot).
Lighthouse report menu highlighting Save as JSON
Recommended naming
  • `before-desktop-run-01.json`
  • `before-mobile-run-01.json`
  • `after-desktop-run-01.json`
  • `after-mobile-run-01.json`
Tips
  • Run each scenario multiple times for stable averages.
  • Use the same URL and test conditions when possible.
  • Prefer Incognito to reduce extension noise.

3) Upload and compare

  • Upload one complete pair to compare only one device: `Before Desktop + After Desktop` or `Before Mobile + After Mobile`.
  • You can also upload both devices together to compare Desktop and Mobile in the same run.
  • Drop JSON files directly or drop/select a folder to import JSON files automatically.
  • Click Compare results.