Lighthouse Isn't Something You Install Anymore

Introduction

Lighthouse is Google's open-source auditing tool for web pages — it loads a page, runs it through a battery of checks, and scores it across four categories. What it isn't anymore is something you install. It ships built into Chrome's DevTools, so it's already on your machine if you have Chrome.

How to Run It

Three ways, depending on what you're doing:

• Chrome DevTools. Open DevTools (F12 or right-click → Inspect), go to the Lighthouse tab, pick your categories and device type, click "Analyze page load." This is the version most people actually want.
• PageSpeed Insights (pagespeed.web.dev). Paste a URL, no browser tab required — useful for checking a live page from any device, or sharing a result with someone who doesn't have DevTools open.
• The command line (the lighthouse npm package), for automated runs in CI so a performance regression gets caught before it ships instead of after someone complains.

Every method runs the same audits and produces the same kind of report — an overall score per category plus a specific, prioritized list of what to fix, exportable as HTML or JSON.

The Four Scores

Performance

How fast the page actually becomes usable — not just when something appears on screen, but when a visitor can interact with it. Lighthouse measures this through metrics like load time, first meaningful paint, time to interactive, and estimated network round-trip time. This is the score most closely tied to whether visitors stick around; see what we found auditing our own site for what actually moved this number.

Accessibility

Checks against WCAG 2.0 standards and ARIA roles — things like whether images have alt text, whether color contrast is sufficient, and whether the page works with keyboard navigation and screen readers. Most flagged issues here are small, specific fixes once you see them: a missing label, a contrast ratio a shade too low. Ignoring this score doesn't just risk excluding real visitors — for federal agencies and their contractors, it's also a Section 508 compliance question.

Best Practices

A grab-bag of modern web hygiene: whether the site serves over HTTPS, whether images use correct aspect ratios, whether the console is throwing errors, whether libraries with known vulnerabilities are in use. Individually small, collectively a decent proxy for whether the codebase is being maintained.

SEO

Whether the page is actually crawlable and indexable — meta descriptions and titles present, links crawlable, mobile-friendly viewport configured, valid canonical tags. This score checks the mechanics that let a search engine understand the page; it doesn't and can't judge whether the content itself is any good.

A note on a category that used to exist here: earlier versions of Lighthouse also scored Progressive Web App capabilities (offline support, installability) as a fifth category. That's since moved to a separate installability check in DevTools rather than a scored category in the main report — worth knowing if you're following an older guide that references it.

Conclusion

A perfect 100 across all four isn't the goal — diminishing returns set in fast, and some flagged items won't matter for your specific site. The useful habit is running it regularly enough to catch regressions, and treating a dropping Performance or Accessibility score as a real signal instead of noise. Pair it with a real performance audit when the score alone doesn't tell you which fix actually matters most.

Tyrone Showers