# Lighthouse

Category: [Performance & Core Web Vitals](https://seo-geo-glossary.com/en/glossary/category/performance-core-web-vitals/) › [Basics & measurement](https://seo-geo-glossary.com/en/glossary/category/performance-core-web-vitals/basics-measurement/) · Also known as: Google Lighthouse

**Lighthouse** is, in the web context, an open-source, automated tool from Google that audits the quality of web pages. It loads a URL, tests it and produces a report with scores and recommendations for each failed audit. It is unrelated to lighthouses, Microsoft 365 Lighthouse or other products of the same name.

## What does Lighthouse check?

The categories named in Chrome's documentation are Performance, Accessibility, Best Practices and SEO. The overview page also lists a newer category, Agentic browsing. Each audit explains what it found and how to fix it. Reports can be saved as JSON and shared.

## How can you run it?

- In Chrome DevTools
- As a command-line tool or Node module (both need Chrome installed)
- Through the PageSpeed Insights web interface
- As a Chrome extension

It works on any URL, including pages behind a login when run locally.

## How is the performance score built?

The performance score from 0 to 100 is a weighted mix of metrics. For Lighthouse 10, the documentation lists:

| Metric | Weight |
|---|---|
| First Contentful Paint | 10% |
| Speed Index | 10% |
| Largest Contentful Paint | 25% |
| Total Blocking Time | 30% |
| Cumulative Layout Shift | 25% |

Scores of 90 to 100 are green, 50 to 89 orange and 0 to 49 red. Lighthouse maps a metric value to a score using a curve based on HTTP Archive data: the 25th percentile of the data corresponds to a score of 50, and the 8th percentile to 90.

## Lab data and field data

Lighthouse measures in a simulated environment, so the result is lab data. PageSpeed Insights shows Lighthouse results as its lab section and CrUX data from real users as its field section.

## Example

A Lighthouse run on a landing page returns a performance score of 72 (orange). The report lists Total Blocking Time as the weakest metric. Because TBT carries the highest weight of 30 percent, reducing JavaScript execution moves the score more than a change to Speed Index would.

## Not to be confused with

- [Field data vs. lab data](https://seo-geo-glossary.com/en/glossary/field-data-vs-lab-data/index.md): describes whether values come from real users (field data, for example from CrUX) or from a simulated measurement (lab data). Lighthouse provides lab data.

## Related terms

- [PageSpeed Insights](https://seo-geo-glossary.com/en/glossary/pagespeed-insights/index.md)
- [Core Web Vitals](https://seo-geo-glossary.com/en/glossary/core-web-vitals/index.md)
- [Field data vs. lab data](https://seo-geo-glossary.com/en/glossary/field-data-vs-lab-data/index.md)
- [Total Blocking Time (TBT)](https://seo-geo-glossary.com/en/glossary/total-blocking-time/index.md)
- [Speed Index](https://seo-geo-glossary.com/en/glossary/speed-index/index.md)
- [Largest Contentful Paint (LCP)](https://seo-geo-glossary.com/en/glossary/largest-contentful-paint/index.md)

## Sources

- [Introduction to Lighthouse – Chrome for Developers](https://developer.chrome.com/docs/lighthouse/overview)
- [Lighthouse performance scoring – Chrome for Developers](https://developer.chrome.com/docs/lighthouse/performance/performance-scoring)
- [About PageSpeed Insights – Google for Developers](https://developers.google.com/speed/docs/insights/v5/about)

---

Last updated: October 8, 2026
URL: https://seo-geo-glossary.com/en/glossary/lighthouse/