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Google Lighthouse audits a web page for performance, accessibility, best practices, and SEO. Run it before making changes to establish a baseline, use its metrics and audit explanations to choose a focused improvement, then rerun under comparable conditions. Its scores are useful diagnostics—not a complete measure of every visitor’s experience or proof that a page is accessible to everyone.
What Google Lighthouse measures
Lighthouse is an open-source, automated tool for evaluating the quality of web pages. Give it a URL or audit the page open in your browser; it produces a report with results and suggestions. Its documented audit areas include performance, accessibility, best practices, and SEO. It can audit public pages as well as pages that require authentication. Chrome’s Lighthouse overview describes the available workflows.
A Lighthouse report is a starting point for investigation. It flags conditions its automated checks can detect; it does not replace reviewing how the page works for real people. The useful question is not simply “What score did I get?” but “Which finding points to a change that matters, and can I verify the change?”
Choose how to run an audit
| Workflow | Best fit | Important consideration |
|---|---|---|
| Chrome DevTools | Interactive checks, local pages, and pages requiring authentication | Audit the page open in Chrome; useful when a URL is not publicly reachable. |
| Lighthouse CLI | Repeatable command-line audits and automation | Requires Chrome installed. |
| Node | Integrating Lighthouse into a script or development workflow | Requires Chrome installed. |
| PageSpeed Insights | A web-based audit of a URL | Convenient for public pages without setting up a local command-line workflow. |
For regression checks in a development process, Chrome also documents Lighthouse CI. Choose DevTools when you need to inspect a local or authenticated page interactively; use CLI or Node when you need repeatable automation; choose PageSpeed Insights when a web interface for a URL is the simplest route.
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Run a Lighthouse audit in Chrome DevTools
- Open the page in Chrome. Navigate to the page you want to inspect. For local or authenticated pages, use the browser session in which that page is available.
- Open DevTools. Use Chrome’s menu or your operating system’s keyboard shortcut to open Developer Tools.
- Open the Lighthouse panel. Select the Lighthouse tab in DevTools. If it is not visible, use the panel overflow menu to find it.
- Choose the audit categories and device mode. Select the areas you want to evaluate, such as Performance, Accessibility, Best Practices, or SEO, and the device class appropriate to the question.
- Run the audit. Start the analysis and let Lighthouse load and inspect the page.
- Review the report. Inspect the metrics, failed audits, opportunities, and diagnostics. Open an audit’s explanation to see what it checks and what kind of remediation it suggests.
- Make one targeted change and rerun. Keeping the change focused helps you see whether it affected the finding or metric you were trying to improve.
The exact DevTools appearance can vary by Chrome version. For current panel guidance, see Chrome’s Lighthouse tutorial.
Run Lighthouse from the command line or Node
CLI and Node workflows are suited to scripting and repeatable checks, but both require Chrome installed. The official overview links to the Lighthouse project and command-line guidance. Before automating, decide what output your workflow needs and keep the browser and audit conditions consistent across runs.
A simple CLI run uses a page URL as its input:
npx lighthouse https://example.comThis command invokes Lighthouse through npm’s package runner. A successful run produces a report; consult the CLI documentation for options such as output format and destination rather than assuming a default format will suit a CI pipeline. In a script or build job, pin and manage the Lighthouse package according to your project’s dependency practices, and make Chrome available in that environment.
Node integration is useful when a script needs to launch Lighthouse and consume its results. Follow the current package documentation for the API and options; do not assume that a command-line flag and a Node option have identical names. In CI, Lighthouse CI provides a separate workflow for tracking and preventing regressions, with configuration documented by the project.
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Interpret scores and findings carefully
Performance is a diagnostic snapshot
The Performance score is derived from measured performance metrics. The score can vary because conditions outside the page itself change, including A/B tests, ad delivery, network routing, device differences, injected browser-extension code, or antivirus software. Chrome’s performance scoring documentation explains the scoring model and variability. Treat a score as a snapshot of one audit, then inspect the underlying metrics and audit details to decide what to address.
For a useful before-and-after comparison, keep the device class and browser setup alike, and avoid unrelated tabs or extensions. An apparent score change under different conditions may not reflect a change in the page. Also, do not rely on historical metric-weight tables as current: weights can be version-specific, and a current release’s exact weights are not established here.
Accessibility score cannot certify accessibility
Lighthouse’s accessibility score is a weighted average of automated audits that pass or fail. Manual audits and low-impact or best-practice audits do not affect that score. A high score therefore does not prove that every user can access the page. Pair automated results with manual review and appropriate assistive-technology testing. See Chrome’s accessibility scoring explanation.
Do not treat historic PWA audits as a current checklist
Chrome marks Lighthouse PWA testing as deprecated. Its historic PWA audit results should not be treated as a current installability checklist; use current PWA guidance instead. Chrome’s PWA audit documentation states the deprecation.
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Turn a report into improvements
- Establish a baseline. Run an audit before changing the page so you have a record of its current findings.
- Identify a specific finding. Review the metrics, failed audits, opportunities, and diagnostics. Read the linked explanation for the check instead of treating its label as a complete fix.
- Choose a targeted change. Prioritize a change relevant to the page and the finding. Lighthouse suggestions are not a substitute for understanding the application or the impact on users.
- Change one thing at a time. The DevTools tutorial recommends this approach so you can see the isolated effect of an edit.
- Rerun under comparable conditions. Keep device class and browser setup consistent. Compare the metric-level details as well as the overall score.
- Verify the real page. Check that the change works as intended for the page’s users; an automated audit cannot cover every interaction or accessibility need.
If an audit errors rather than producing a report, Chrome’s tutorial suggests trying an incognito window with no other tabs open. Extensions can interfere with auditing, so also check whether disabling them resolves the issue.
Common Lighthouse problems and fixes
| Symptom | Likely explanation | What to try |
|---|---|---|
| The audit errors or will not complete | A browser extension or another open tab may interfere. | Try an incognito window with no other tabs, as the DevTools tutorial recommends. |
| The score changes between runs without an obvious code change | Ads, A/B tests, network routing, device conditions, extensions, or antivirus software can affect results. | Repeat with the same device class and browser setup, limit other tabs and extensions, and compare the underlying metrics. |
| The report flags an issue but the recommended change is unclear | An audit label alone may not explain the check or its context. | Open the audit’s linked explanation, then inspect the page and choose a targeted change. |
| A page cannot be audited through a public URL workflow | The page may be local or require authentication. | Open it in Chrome and use DevTools in the session where it is accessible. |
| A CLI or Node audit cannot launch a browser | These workflows require Chrome installed in the environment running the audit. | Install or expose Chrome to that environment, then rerun. |
Capture a page screenshot without confusing it with an audit
Lighthouse evaluates page quality; a screenshot is a visual record of what a browser rendered. A screenshot alone does not provide Lighthouse metrics, audit checks, or a performance score. If you need a visual artifact alongside an audit, capture the page separately and interpret the two outputs for their distinct purposes.
For local hands-on inspection, Chrome DevTools can capture a screenshot from the browser session you are auditing. For a screenshot API or agent workflow, ScreenshotNeo is an option: it removes known consent banners, newsletter popups, and chat widgets before capture, bills only clean shots, and provides an MCP server for AI agents. This does not replace running Lighthouse.
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ScreenshotNeo can return a screenshot with one GET request. The example captures a page as WebP; see the ScreenshotNeo API documentation for request options.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpCookie banners, popups, and chat widgets are removed before the shot. Bot checks, blank pages, and failed loads are never billed. Its MCP server lets AI agents take screenshots, and the Free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000. Sign up for ScreenshotNeo’s free plan.
Frequently Asked Questions
Does Lighthouse test a website’s real-world experience for every visitor?
No. An audit is a measurement under particular conditions. Compare runs consistently and use the metric-level findings alongside other evidence about the page.
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Can a high Lighthouse accessibility score prove a page is accessible?
No. Manual audits do not affect the accessibility score, so automated results need manual review and appropriate assistive-technology testing.
Can Lighthouse audit a page that requires a login?
Yes. For a local or authenticated page, use Chrome DevTools in the browser session where the page is available.
Does Lighthouse still provide a current PWA installability audit?
Lighthouse PWA testing is marked deprecated. Do not use historic PWA audit results as a current installability checklist.
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