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Lighthouse analyzes web apps and web pages, collecting modern performance metrics and insights on developer best practices.

Using Lighthouse in Chrome DevTools

Lighthouse is integrated directly into the Chrome DevTools, under the "Lighthouse" panel.

Installation: install Chrome.

Run it: open Chrome DevTools, select the Lighthouse panel, and hit "Generate report".

<img width="550" alt="Lighthouse integration in Chrome DevTools." src="https://user-images.githubusercontent.com/2766281/204185043-9c49abe5-baee-4b26-b5ce-ece410661213.png">

Using the Chrome extension

The Chrome extension was available prior to Lighthouse being available in Chrome Developer Tools, and offers similar functionality.

Installation: install the extension from the Chrome Web Store.

Run it: follow the extension quick-start guide.

Using the Node CLI

The Node CLI provides the most flexibility in how Lighthouse runs can be configured and reported. Users who want more advanced usage, or want to run Lighthouse in an automated fashion should use the Node CLI.

Note Lighthouse requires Node 18 LTS (18.x) or later.

Installation:

npm install -g lighthouse
# or use yarn:
# yarn global add lighthouse

Run it: lighthouse https://airhorner.com/

By default, Lighthouse writes the report to an HTML file. You can control the output format by passing flags.

CLI options

<!-- To update the help output: node cli --help | pbcopy --> 
$ lighthouse --help

lighthouse <url> <options>

Logging:
  --verbose  Displays verbose logging  [boolean] [default: false]
  --quiet    Displays no progress, debug logs, or errors  [boolean] [default: false]

Configuration:
  --save-assets                  Save the trace contents & devtools logs to disk  [boolean] [default: false]
  --list-all-audits              Prints a list of all available audits and exits  [boolean] [default: false]
  --list-trace-categories        Prints a list of all required trace categories and exits  [boolean] [default: false]
  --additional-trace-categories  Additional categories to capture with the trace (comma-delimited).  [string]
  --config-path                  The path to the config JSON.
                                 An example config file: core/config/lr-desktop-config.js  [string]
  --preset                       Use a built-in configuration.
                                 WARNING: If the --config-path flag is provided, this preset will be ignored.  [string] [choices: "perf", "experimental", "desktop"]
  --chrome-flags                 Custom flags to pass to Chrome (space-delimited). For a full list of flags, see https://bit.ly/chrome-flags
                                 Additionally, use the CHROME_PATH environment variable to use a specific Chrome binary. Requires Chromium version 66.0 or later. If omitted, any detected Chrome Canary or Chrome stable will be used.  [string] [default: ""]
  --port                         The port to use for the debugging protocol. Use 0 for a random port  [number] [default: 0]
  --hostname                     The hostname to use for the debugging protocol.  [string] [default: "localhost"]
  --form-factor                  Determines how performance metrics are scored and if mobile-only audits are skipped. For desktop, --preset=desktop instead.  [string] [choices: "mobile", "desktop"]
  --screenEmulation              Sets screen emulation parameters. See also --preset. Use --screenEmulation.disabled to disable. Otherwise set these 4 parameters individually: --screenEmulation.mobile --screenEmulation.width=360 --screenEmulation.height=640 --screenEmulation.deviceScaleFactor=2
  --emulatedUserAgent            Sets useragent emulation  [string]
  --max-wait-for-load            The timeout (in milliseconds) to wait before the page is considered done loading and the run should continue. WARNING: Very high values can lead to large traces and instability  [number]
  --enable-error-reporting       Enables error reporting, overriding any saved preference. --no-enable-error-reporting will do the opposite. More: https://github.com/GoogleChrome/lighthouse/blob/main/docs/error-reporting.md  [boolean]
  --gather-mode, -G              Collect artifacts from a connected browser and save to disk. (Artifacts folder path may optionally be provided). If audit-mode is not also enabled, the run will quit early.
  --audit-mode, -A               Process saved artifacts from disk. (Artifacts folder path may be provided, otherwise defaults to ./latest-run/)
  --only-audits                  Only run the specified audits  [array]
  --only-categories              Only run the specified categories. Available categories: accessibility, best-practices, performance, seo  [array]
  --skip-audits                  Run everything except these audits  [array]
  --disable-full-page-screenshot Disables collection of the full page screenshot, which can be quite large  [boolean]

Output:
  --output       Reporter for the results, supports multiple values. choices: "json", "html", "csv"  [array] [default: ["html"]]
  --output-path  The file path to output the results. Use 'stdout' to write to stdout.
                   If using JSON output, default is stdout.
                   If using HTML or CSV output, default is a file in the working directory with a name based on the test URL and date.
                   If using multiple outputs, --output-path is appended with the standard extension for each output type. "reports/my-run" -> "reports/my-run.report.html", "reports/my-run.report.json", etc.
                   Example: --output-path=./lighthouse-results.html  [string]
  --view         Open HTML report in your browser  [boolean] [default: false]

Options:
  --version                            Show version number  [boolean]
  --help                               Show help  [boolean]
  --cli-flags-path                     The path to a JSON file that contains the desired CLI flags to apply. Flags specified at the command line will still override the file-based ones.
  --locale                             The locale/language the report should be formatted in
  --blocked-url-patterns               Block any network requests to the specified URL patterns  [array]
  --disable-storage-reset              Disable clearing the browser cache and other storage APIs before a run  [boolean]
  --throttling-method                  Controls throttling method  [string] [choices: "devtools", "provided", "simulate"]
  --throttling
  --throttling.rttMs                   Controls simulated network RTT (TCP layer)
  --throttling.throughputKbps          Controls simulated network download throughput
  --throttling.requestLatencyMs        Controls emulated network RTT (HTTP layer)
  --throttling.downloadThroughputKbps  Controls emulated network download throughput
  --throttling.uploadThroughputKbps    Controls emulated network upload throughput
  --throttling.cpuSlowdownMultiplier   Controls simulated + emulated CPU throttling
  --extra-headers                      Set extra HTTP Headers to pass with request
  --precomputed-lantern-data-path      Path to the file where lantern simulation data should be read from, overwriting the lantern observed estimates for RTT and server latency.  [string]
  --lantern-data-output-path           Path to the file where lantern simulation data should be written to, can be used in a future run with the `precomputed-lantern-data-path` flag.  [string]
  --plugins                            Run the specified plugins  [array]
  --channel  [string] [default: "cli"]
  --chrome-ignore-default-flags  [boolean] [default: false]

Examples:
  lighthouse <url> --view                                                                          Opens the HTML report in a browser after the run completes
  lighthouse <url> --config-path=./myconfig.js                                                     Runs Lighthouse with your own configuration: custom audits, report generation, etc.
  lighthouse <url> --output=json --output-path=./report.json --save-assets                         Save trace, screenshots, and named JSON report.
  lighthouse <url> --screenEmulation.disabled --throttling-method=provided --no-emulatedUserAgent  Disable device emulation and all throttling
  lighthouse <url> --chrome-flags="--window-size=412,660"                                          Launch Chrome with a specific window size
  lighthouse <url> --quiet --chrome-flags="--headless"                                             Launch Headless Chrome, turn off logging
  lighthouse <url> --extra-headers "{\"Cookie\":\"monster=blue\", \"x-men\":\"wolverine\"}"        Stringify'd JSON HTTP Header key/value pairs to send in requests
  lighthouse <url> --extra-headers=./path/to/file.json                                             Path to JSON file of HTTP Header key/value pairs to send in requests
  lighthouse <url> --only-categories=performance,seo                                               Only run the specified categories. Available categories: accessibility, best-practices, performance, seo

For more information on Lighthouse, see https://developers.google.com/web/tools/lighthouse/.
Output Examples
lighthouse
# saves `./<HOST>_<DATE>.report.html`

lighthouse --output json
# json output sent to stdout

lighthouse --output html --output-path ./report.html
# saves `./report.html`

# NOTE: specifying an output path with multiple formats ignores your specified extension for *ALL* formats
lighthouse --output json --output html --output-path ./myfile.json
# saves `./myfile.report.json` and `./myfile.report.html`

lighthouse --output json --output html
# saves `./<HOST>_<DATE>.report.json` and `./<HOST>_<DATE>.report.html`

lighthouse --output-path=~/mydir/foo.out --save-assets
# saves `~/mydir/foo.report.html`
# saves `~/mydir/foo-0.trace.json` and `~/mydir/foo-0.devtoolslog.json`

lighthouse --output-path=./report.json --output json
# saves `./report.json`
Lifecycle Examples

You can run a subset of Lighthouse's lifecycle if desired via the --gather-mode (-G) and --audit-mode (-A) CLI flags.

lighthouse http://example.com -G
# launches browser, collects artifacts, saves them to disk (in `./latest-run/`) and quits

lighthouse http://example.com -A
# skips browser interaction, loads artifacts from disk (in `./latest-run/`), runs audits on them, generates report

lighthouse http://example.com -GA
# Normal gather + audit run, but also saves collected artifacts to disk for subsequent -A runs.


# You can optionally provide a custom folder destination to -G/-A/-GA. Without a value, the default will be `$PWD/latest-run`.
lighthouse -GA=./gmailartifacts https://gmail.com

Notes on Error Reporting

The first time you run the CLI you will be prompted with a message asking you if Lighthouse can anonymously report runtime exceptions. The Lighthouse team uses this information to detect new bugs and avoid regressions. Opting out will not affect your ability to use Lighthouse in any way. Learn more.

Using the Node module

You can also use Lighthouse programmatically with the Node module.

Read Using Lighthouse programmatically for help getting started.
Read Lighthouse Configuration to learn more about the configuration options available.

Viewing a report

Lighthouse can produce a report as JSON or HTML.

HTML report:

<img src="https://raw.githubusercontent.com/GoogleChrome/lighthouse/443ff2c8a297dfd2297dfaca86c4966a87c8574a/assets/example_audit.png" alt="Lighthouse example audit" width="500px">

Online Viewer

Running Lighthouse with the --output=json flag generates a JSON dump of the run. You can view this report online by visiting https://googlechrome.github.io/lighthouse/viewer/ and dragging the file onto the app. You can also use the "Export" button from the top of any Lighthouse HTML report and open the report in the Lighthouse Viewer.

In the Viewer, reports can be shared by clicking the share icon in the top right corner and signing in to GitHub.

Note: shared reports are stashed as a secret Gist in GitHub, under your account.

Docs & Recipes

Useful documentation, examples, and recipes to get you started.

Docs

Recipes

Videos

The session from Google I/O 2018 covers the new performance engine, upcoming Lighthouse REST API, and using the Chrome UX report to evaluate real-user data.

Watch the Lighthouse @ Google I/O 2018 session.

The session from Google I/O 2017 covers architecture, writing custom audits, GitHub/Travis/CI integration, headless Chrome, and more:

Watch the Lighthouse @ Google I/O 2017 session.

Click the image to watch the video on YouTube.

Develop

Read on for the basics of hacking on Lighthouse. Also, see Contributing for detailed information.

Setup

# yarn should be installed first

git clone https://github.com/GoogleChrome/lighthouse

cd lighthouse
yarn
yarn build-all

Run

node cli http://example.com
# append --chrome-flags="--no-sandbox --headless --disable-gpu" if you run into problems connecting to Chrome

Getting started tip: node --inspect-brk cli http://example.com to open up Chrome DevTools and step through the entire app. See Debugging Node.js with Chrome DevTools for more info.

Tests

# lint and test all files
yarn test

# run all unit tests
yarn unit

# run a given unit test (e.g. core/test/audits/byte-efficiency/uses-long-cache-ttl-test.js)
yarn mocha uses-long-cache-ttl

# watch for file changes and run tests
#   Requires http://entrproject.org : brew install entr
yarn watch

## run linting, unit, and smoke tests separately
yarn lint
yarn unit
yarn smoke

## run tsc compiler
yarn type-check

Docs

Some of our docs have tests that run only in CI by default. To modify our documentation, you'll need to run yarn build-pack && yarn test-docs locally to make sure they pass.

Additional Dependencies

Lighthouse Integrations in Web Perf services

This section details services that have integrated Lighthouse data. If you're working on a cool project integrating Lighthouse and would like to be featured here, file an issue to this repo or tweet at us @_____lighthouse!

Lighthouse Integrations in non-Web Perf services

Plugins

Related projects

Other awesome open source projects that use Lighthouse.

FAQ

How does Lighthouse work?

See Lighthouse Architecture.

Why is the performance score so low? It looks fine to me.

Lighthouse reports the performance metrics as they would be experienced by a typical mobile user on a 4G connection and a mid-tier ~$200 phone. Even if it loads quickly on your device and network, users in other environments will experience the site very differently.

Read more in our guide to throttling.

Why does the performance score change so much?

Lighthouse performance scores will change due to inherent variability in web and network technologies, even if there hasn't been a code change. Test in consistent environments, run Lighthouse multiple times, and beware of variability before drawing conclusions about a performance-impacting change.

Read more in our guide to reducing variability.

Can I configure the lighthouse run?

Yes! Details in Lighthouse configuration.

How does Lighthouse use network throttling, and how can I make it better?

Good question. Network and CPU throttling are applied by default in a Lighthouse run. The network attempts to emulate slow 4G connectivity and the CPU is slowed down 4x from your machine's default speed. If you prefer to run Lighthouse without throttling, you'll have to use the CLI and disable it with the --throttling.* flags mentioned above.

Read more in our guide to network throttling.

Are results sent to a remote server?

Nope. Lighthouse runs locally, auditing a page using a local version of the Chrome browser installed on the machine. Report results are never processed or beaconed to a remote server.

How do I get localized Lighthouse results via the CLI?

Starting in Lighthouse 8.0, Lighthouse relies entirely on native Intl support and no longer uses an Intl polyfill. If you're using Node 14 or later, there should be no issue because Node is now built with full-icu by default.

However, if you're using a small-icu Node build, you may see Lighthouse log messages about your locale not being available. To remedy this, you can manually install ICU data by using the full-icu module and the --icu-data-dir node flag at launch.

How do I author custom audits to extend Lighthouse?

Tip: see Lighthouse Architecture for more information on terminology and architecture.

Lighthouse can be extended to run custom audits and gatherers that you author. This is great if you're already tracking performance metrics in your site and want to surface those metrics within a Lighthouse report.

If you're interested in running your own custom audits, check out our Custom Audit Example over in recipes.

How do I contribute?

We'd love help writing audits, fixing bugs, and making the tool more useful! See Contributing to get started.

<p align="center"> <img src="./assets/lighthouse-logo_512px.png" alt="Lighthouse logo" height="150"> <br> <b>Lighthouse</b>, ˈlītˌhous (n): a <s>tower or other structure</s> tool containing a beacon light to warn or guide <s>ships at sea</s> developers. </p>