What can Lighthouse tell you about one page?
Lighthouse runs automated checks on a page and shows specific findings, such as a large image slowing the initial load or a button with no name that assistive technology can read. Open the page in Chrome, open Developer Tools and choose Lighthouse to start a report.
Use a sample page you control. You can check a local page or a page you already have permission to open. Avoid sharing private addresses, customer records or signed-in reports.
How do you know whether one change helped?
Run a baseline report and pick one finding. For a test landing page with a large banner image, try a smaller version and rerun the audit on the same page. Compare the image size and the relevant finding as well as any timing change.
- Keep the conditions steadyUse the same browser, audit mode and device setting. Close unrelated tabs and repeat the runs if the timing varies.
- Check the actual pageOpen it at phone width and check that the image is still readable. Keep the change if it improves the finding without making the page harder to use.
Can a high score tell you whether people can use the page?
Lighthouse combines automated checks into an accessibility score. Open the individual findings to see which checks failed. The score leaves manual questions open, including whether you can finish a task with a keyboard and whether a screen reader announces what happened.
Start at the top of a test form and use Tab to move through it. Check that focus is visible, the order makes sense, and you can open, close and submit the form. Use sample data and confirm the form is connected only to test services before you submit.
Why do the report and real visitors sometimes disagree?
A Lighthouse run measures a test under particular conditions. Real visitors use different phones, connections and pages. PageSpeed Insights can show both a Lighthouse result and separate real-user data when it has enough observations.
Use the test report to investigate a specific change. In PageSpeed Insights, check whether the real-user numbers describe This URL or the whole site. A new or low-traffic page can have a test result without enough visits for its own real-user summary.
What do you need to run and keep a report?
The Lighthouse tool is open source and available in Chrome Developer Tools. Start with the browser report before adding a service that tracks results over time. If you automate audits later, budget for the computers or build service that run them.
Keep the tested address or build, browser and device settings, and the finding you were trying to improve. Keep reports from private pages within the team that has access to them.