Google Lighthouse is a free, open-source tool that audits a web page for performance, accessibility, best practices, and SEO. Run it in Chrome DevTools for an interactive audit—including local or authenticated pages—or use PageSpeed Insights for a web-based report and the CLI or Node.js when you need automation. Treat the report as a diagnostic snapshot: use its metric-level findings to choose a fix, then rerun under comparable conditions to see whether the change helped.
What Lighthouse measures
Lighthouse runs automated checks against a page and produces a report with results, audit details, and suggestions. Its documented audit areas include:
- Performance: measured page-performance metrics and related audit findings.
- Accessibility: automated checks for some accessibility issues.
- Best practices: checks related to web-development practices.
- SEO: automated checks related to search-engine optimization.
The tool can audit public pages, as well as pages that require authentication. Which workflow is appropriate depends on where the page is and whether you need a one-off report or repeatable automation.
Choose where to run an audit
| Workflow | Best fit | Important constraint |
|---|---|---|
| Chrome DevTools | Interactive audits, including local or authenticated pages. | Run the audit in the browser where the target page is open. |
| PageSpeed Insights | A web interface for auditing a URL. | Use it when you want to submit a URL and view a web-based report. |
| Lighthouse CLI | Scripted audits and automation. | Chrome must be installed. |
| Lighthouse Node.js | Auditing from a Node-based workflow. | Chrome must be installed. |
Lighthouse CI is also documented as a way to help prevent regressions. The exact setup depends on your project and deployment workflow; do not assume that a single local run is equivalent to a configured CI check.
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Run an audit in Chrome DevTools
- Open the page you want to examine in Chrome. For a local or authenticated page, first navigate to it and complete any required sign-in.
- Open Chrome DevTools and select the Lighthouse panel.
- Choose the audit categories and device configuration available in the panel that match your question, then start the audit.
- When the report appears, inspect the performance metrics, failed audits, opportunities, and diagnostics. Open an audit’s linked explanation to understand what it checks and what changes it suggests.
- Make one targeted change and run the audit again. Changing one thing at a time makes it easier to judge which change affected the result.
Chrome’s interface can change over time, so if the panel is not immediately visible, use DevTools’ panel menu to find Lighthouse. For a report on a page that is not open in your browser, use PageSpeed Insights or an automation workflow instead.
Run a URL audit with PageSpeed Insights
- Open PageSpeed Insights in a browser.
- Enter the public page URL you want to audit and submit it.
- Review the report and its underlying metrics and audit findings, rather than relying on the overall score alone.
This workflow is suited to a URL-based, web-interface audit. If the page is local or requires authentication, DevTools is the documented practical choice because you can audit the page already open in your browser.
Run Lighthouse from the command line or Node.js
CLI and Node workflows are useful when audits need to run from scripts or an automation pipeline. Both require Chrome installed. The specific command, configuration, and output handling depend on how your project is set up; use the Lighthouse documentation for the current installation and invocation steps rather than copying an unverified version-specific command. For regression checks across builds, consider the documented Lighthouse CI workflow.
Automation does not remove the need to interpret results. Keep the target page, browser setup, and measurement conditions consistent between runs, and investigate the metric-level findings behind a changed score.
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- Record a baseline. Audit before changing the page. Note the relevant metrics and failed audits so you can compare later.
- Investigate the finding. Read the audit explanation and inspect the page itself. A failed audit is a clue about the page, not a replacement for examining what users actually experience.
- Choose a targeted change. Select a fix that addresses a specific finding or user-facing problem, rather than making several unrelated changes at once.
- Rerun the audit. Use the same device class and browser setup where possible. Compare the resulting metrics and audit details with the baseline.
- Check the real experience too. Confirm that the change works for the page and users you care about; automated results alone do not establish that every visitor has the same experience.
One-at-a-time changes make cause and effect easier to understand. If a score or metric shifts unexpectedly, first check whether the runs were truly comparable before attributing the difference to your code.
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How to read Lighthouse scores responsibly
Performance score
The Performance score is based on measured performance metrics. Treat it as a snapshot of a particular run, not a direct measurement of every visitor’s experience or a guarantee that a page is fast in all conditions. The metric-level results and audit findings are more useful for deciding what to investigate than the headline score alone.
Scores can vary for reasons beyond a code change: A/B tests, changing ads, network routing, device differences, injected browser-extension code, or antivirus software can affect a run. Compare results only when the conditions are reasonably similar, and investigate the underlying metrics if a score changes.
Accessibility score
Lighthouse accessibility scoring 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 result therefore does not prove that every user can access the page. Pair automated checks with manual review and suitable assistive-technology testing.
SEO and best-practice findings
Use these categories as automated checks that can point to issues worth reviewing. A report does not, by itself, establish the complete quality of a page or its real-world search performance. Read the individual audit explanations and verify changes against the page’s purpose.
Make runs more comparable
- Use the same device class and browser setup for the before-and-after runs.
- Close unrelated tabs and limit extensions that may inject code or interfere.
- Be aware that A/B tests, ad changes, network routing, device variation, and antivirus software can shift results.
- When an audit errors, try an incognito window with no other tabs open; extensions can interfere with auditing.
- Record what changed between runs so you do not mistake a different test condition for an improvement or regression.
What Lighthouse does not establish
- A single score does not represent the experience of every visitor or every device and network condition.
- A successful automated accessibility score is not a full accessibility assessment; manual review and assistive-technology testing remain important.
- Historic Lighthouse PWA audit results should not be treated as a current installability checklist. Lighthouse PWA testing is deprecated; use current PWA guidance instead.
- Do not assume old score weights or thresholds apply to a current run. The exact current release and current Performance metric weights are not established here, so avoid relying on historic version-specific percentages.
Use screenshots alongside an audit when visuals matter
Lighthouse evaluates automated audit criteria; a screenshot can help you inspect what a page looks like at a particular viewport. They answer different questions: a screenshot is not a Lighthouse score, and it does not replace performance or accessibility checks. For repeatable captures of public pages, ScreenshotNeo is a screenshot API and MCP server; it can complement an audit when you need visual evidence for a page state.
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For a screenshot—not a Lighthouse audit—one GET request can capture a page. See the ScreenshotNeo API documentation for options and response details.
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Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshooting common audit problems
The audit errors or does not complete
Try the DevTools tutorial’s suggested isolation step: open an incognito window with no other tabs open and rerun the audit. Extensions can interfere. If you are using CLI or Node, confirm that Chrome is installed, as those workflows require it.
The score changed even though the page did not
Do not assume the difference came from your code. Check for changes in A/B tests, ads, network route, device, injected extension code, or antivirus behavior. Rerun with a consistent browser setup and compare the underlying metrics.
The report identifies an issue, but the page seems fine
Open the audit’s explanation and inspect what it checks. Then verify the finding against the actual page and the users’ experience. An audit is a diagnostic clue, not a substitute for that evaluation.
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A high accessibility score seems conclusive
It is not. The score reflects automated pass-or-fail audits, while manual audits do not affect it. Add manual review and appropriate assistive-technology testing.
You are using Lighthouse PWA results to check installability
Do not rely on the deprecated Lighthouse PWA audit as a current checklist. Consult current PWA guidance for installability instead.
FAQ
Can Lighthouse audit a page behind a login?
Yes. Lighthouse can audit pages requiring authentication; Chrome DevTools is the practical documented option when you can open the signed-in page in the browser.
Does Lighthouse replace testing with assistive technology?
No. Its accessibility score is based on automated audits and is not a complete assessment. Manual review and suitable assistive-technology testing are still needed.
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