MetaMask/metamask-extension

MetaMask Browser Extension

You can find the latest version of MetaMask on our official website. For help using MetaMask, visit our User Support Site.

For general questions, feature requests, or developer questions, visit our Community Forum.

MetaMask supports Firefox, Google Chrome, and Chromium-based browsers. We recommend using the latest available browser version.

For up to the minute news, follow us on X.

To learn how to develop MetaMask-compatible applications, visit our Developer Docs.

To learn how to contribute to the MetaMask codebase, visit our Contributor Docs.

To learn how to contribute to the MetaMask Extension project itself, visit our Extension Docs.

GitHub Codespaces quickstart

As an alternative to building on your local machine, there is a new option to get a development environment up and running in less than 5 minutes by using GitHub Codespaces. Please note that there is a Limited Free Monthly Quota, and after that GitHub will start charging you.

Note: You are billed for both time spent running, and for storage used

1. Start by clicking the button above
2. A new browser tab will open with a remote version of Visual Studio Code (this will take a few minutes to load)
3. A "Simple Browser" will open inside the browser with noVNC -- click Connect
   • Optional steps:
     • Click the button at the upper-right of the Simple Browser tab to open the noVNC window in its own tab
     • Open the noVNC sidebar on the left, click the gear icon, change the Scaling Mode to Remote Resizing
4. Wait about 20 extra seconds on the first launch, for the scripts to finish
5. Right-click on the noVNC desktop to launch Chrome or Firefox with MetaMask pre-installed
6. Change some code, then run yarn start to build in dev mode
7. After a minute or two, it will finish building, and you can see your changes in the noVNC desktop

Tips to keep your Codespaces usage lower

• You are billed for both time spent running, and for storage used
• Codespaces pause after 30 minutes of inactivity, and auto-delete after 30 days of inactivity
• You can manage your Codespaces here: https://github.com/codespaces
  • You may want to manually pause them before the 30 minute timeout
  • If you have several idle Codespaces hanging around for several days, you can quickly run out of storage quota. You should delete the ones you do not plan to use anymore, and probably keep only 1 or 2 in the long-term. It's also possible to re-use old Codespaces and switch the branch, instead of creating new ones and deleting the old ones.

Codespaces on a fork

If you are not a MetaMask Internal Developer, or are otherwise developing on a fork, the default Infura key will be on the Free Plan and have very limited requests per second. If you want to use your own Infura key, follow the .metamaskrc and INFURA_PROJECT_ID instructions in the section Building on your local machine.

Building on your local machine

• Install Node.js version 24

  • If you are using nvm (recommended) running nvm use will automatically choose the right node version for you.

• Enable Corepack by executing the command corepack enable within the metamask-extension project. Corepack is a utility included with Node.js by default. It manages Yarn on a per-project basis, using the version specified by the packageManager property in the project's package.json file. Please note that modern releases of Yarn are not intended to be installed globally or via npm.

• Duplicate .metamaskrc.dist within the root and rename it to .metamaskrc by running cp .metamaskrc{.dist,}.

  • Replace the INFURA_PROJECT_ID value with your own personal Infura API Key.
    • If you don't have an Infura account, you can create one for free on the Infura website.
  • If debugging MetaMetrics, you'll need to add a value for SEGMENT_WRITE_KEY Segment write key, see Developing on MetaMask - Segment.
  • If debugging unhandled exceptions, you'll need to add a value for SENTRY_DSN Sentry Dsn, see Developing on MetaMask - Sentry.
  • Optionally, replace the PASSWORD value with your development wallet password to avoid entering it each time you open the app.
  • If developing with remote feature flags, and you want to override the flags in the build process, you can add a .manifest-overrides.json file to the root of the project and set MANIFEST_OVERRIDES=.manifest-overrides.json in .metamaskrc to the path of the file. This file is used to add flags to manifest.json build files for the extension. You can also modify the _flags.remoteFeatureFlags in the built version of manifest.json in the dist/browser folder to tweak the flags after the build process (these changes will get overwritten when you build again). An example of this remote feature flag overwrite could be:

  {
    "_flags": {
      "remoteFeatureFlags": { "testBooleanFlag": false }
    }
  }
  

• Run yarn install to install the dependencies.

• Build the project to the ./dist/ folder with yarn dist (for Chromium-based browsers) or yarn dist:mv2 (for Firefox)

  • Optionally, to create a development build you can instead run yarn start (for Chromium-based browsers) or yarn start:mv2 (for Firefox)
  • Uncompressed builds can be found in /dist, compressed builds can be found in /builds once they're built.
  • See the build system readme for build system usage information.

• Follow these instructions to verify that your local build runs correctly:

  • How to add custom build to Chrome
  • How to add custom build to Firefox

AI Agent Skills (yarn skills)

AI coding agents (Cursor, Claude Code, Codex) consume shared skills from the MetaMask/skills repo, with an optional private overlay from Consensys/skills. Per ADR #57 this content is not committed here — yarn skills syncs it on demand into local-only paths under .cursor/, .claude/, and .agents/.

Zero-config setup:

yarn install # refreshes the MetaMask/skills cache via the shared `@metamask/skills` CLI
yarn skills  # syncs all default skills through the `metamask-skills sync` command

Optional local configuration:

cp .skills.local.example .skills.local
# edit .skills.local to set SKILLS_DOMAINS or override skills source paths
yarn skills --select                         # interactively pick domains
SKILLS_DOMAINS=perps,testing yarn skills      # one-off domain override

Use .skills.local for persistent skills configuration. Shell environment variables with the same names are supported for one-off or CI overrides and take precedence.

Skipping yarn skills is fine — it only affects agent tooling, not the app build. The repo uses the shared @metamask/skills package so sync/cache behavior stays uniform across MetaMask packages. To opt into best-effort regeneration during install/setup, set SKILLS_AUTO_UPDATE=1 in your shell or .skills.local.

Git Hooks

To get quick feedback from our shared code quality fitness functions before committing the code, you can install our git hooks with Husky.

$ yarn githooks:install

You can read more about them in our testing documentation.

If you are using VS Code and are unable to make commits from the source control sidebar due to a "command not found" error, try these steps from the Husky docs.

Contributing

Development builds

To start a development build (e.g. with logging and file watching) run yarn start.

Development build with wallet state

You can start a development build with a preloaded wallet state, by adding TEST_SRP='<insert SRP here>' and PASSWORD='<insert wallet password here>' to the .metamaskrc file. Then you have the following options:

1. Start the wallet with the default fixture flags, by running yarn start:with-state.
2. Check the list of available fixture flags, by running yarn start:with-state --help.
3. Start the wallet with custom fixture flags, by running yarn start:with-state --FIXTURE_NAME=VALUE for example yarn start:with-state --withAccounts=100. You can pass as many flags as you want. The rest of the fixtures will take the default values.

Advanced Webpack builds

yarn start is backed by Webpack. You can also call yarn webpack directly for advanced build-system debugging; see the Webpack README for more information.

yarn start:lavamoat is not currently supported because Webpack watch mode does not support LavaMoat. For production-like LavaMoat verification, use yarn webpack:lavamoat:build or yarn build:test.

React and Redux DevTools

To use React or Redux DevTools you'll first need to set METAMASK_REACT_REDUX_DEVTOOLS to true in .metamaskrc.

To start the React DevTools, run yarn devtools:react with a development build installed in a browser. This will open in a separate window; no browser extension is required.

To start the Redux DevTools Extension:

• Install the package remotedev-server globally (e.g. yarn global add remotedev-server)
• Install the Redux Devtools extension.
• Open the Redux DevTools extension and check the "Use custom (local) server" checkbox in the Remote DevTools Settings, using the default server configuration (host localhost, port 8000, secure connection checkbox unchecked).

Then run the command yarn devtools:redux with a development build installed in a browser. This will enable you to use the Redux DevTools extension to inspect MetaMask.

To create a development build and run both of these tools simultaneously, run yarn start:dev.

Test Dapp

This test site can be used to execute different user flows.

Running Unit Tests and Linting

Run unit tests and the linter with yarn test. To run just unit tests, run yarn test:unit.

You can run the linter by itself with yarn lint, and you can automatically fix some lint problems with yarn lint:fix. You can also run these two commands just on your local changes to save time with yarn lint:changed and yarn lint:changed:fix respectively.

For Jest debugging guide using Node.js, see docs/tests/jest.md.

Running E2E Tests

Our e2e test suite can be run on either Firefox or Chrome. Here's how to get started with e2e testing:

Preparing a Test Build

Before running e2e tests, ensure you've run yarn install to download dependencies. Next, you'll need a test build. You have 3 options:

1. Use yarn download-builds --build-type test to quickly download and unzip test builds for Chrome and Firefox into the ./dist/ folder. This method is fast and convenient for standard testing.
2. Create a custom production-like Webpack test build. This command allows you to generate test builds for various types, including:
   • yarn build:test for main build
   • yarn build:test:flask for flask build
   • yarn build:test:mv2 for mv2 build
3. Start a Webpack test build with live changes: yarn start:test is particularly useful for development. It starts a test build that automatically recompiles application code upon changes. This option is ideal for iterative testing and development. This command also allows you to generate test builds for various types, including:
   • yarn start:test for main build
   • yarn start:test:flask for flask build
   • yarn start:test:mv2 for mv2 build

Note: The yarn start:test command has LavaMoat and Snow disabled for faster iteration. Use yarn build:test for production-like LavaMoat verification.

Running Tests

Once you have your test build ready, choose the browser for your e2e tests:

• For Firefox, run yarn test:e2e:firefox.
  • Note: If you are running Firefox as a snap package on Linux, ensure you enable the appropriate environment variable: FIREFOX_SNAP=true yarn test:e2e:firefox
• For Chrome, run yarn test:e2e:chrome.

These scripts support additional options for debugging. Use --helpto see all available options.

Specs that have been migrated from Selenium to Playwright (*.pw.spec.ts, see test/e2e/playwright/README.md) run through their own runner:

• For Firefox, run yarn test:e2e:playwright:firefox.
• For Chrome, run yarn test:e2e:playwright:chrome.

One-time setup for the Playwright runner (per machine, and again whenever the Playwright version changes):

yarn                                        # installs the Playwright package
yarn playwright install chromium firefox   # downloads the browser binaries

Running a single e2e test

Single e2e tests can be run with yarn test:e2e:single test/e2e/tests/TEST_NAME.spec.js along with the options below.

  --browser           Set the browser to be used; specify 'chrome', 'firefox', 'all'
                      or leave unset to run on 'all' by default.
                                                          [string] [default: 'all']
  --debug             Run tests in debug mode, logging each driver interaction
                                                         [boolean] [default: true]
  --retries           Set how many times the test should be retried upon failure.
                                                              [number] [default: 0]
  --leave-running     Leaves the browser running after a test fails, along with
                      anything else that the test used (the local node, the
                      test dapp, etc.)                   [boolean] [default: false]
  --update-snapshot   Update E2E test snapshots
                                             [alias: -u] [boolean] [default: false]

For example, to run the account-details tests using Chrome, with debug logging and with the browser set to remain open upon failure, you would use: yarn test:e2e:single test/e2e/tests/account-menu/account-details.spec.js --browser=chrome --leave-running

For migrated Playwright specs, pass the spec path as a positional filter to the Playwright runner instead:

# Run a single spec
yarn test:e2e:playwright:chrome test/e2e/tests/settings/terms-of-use.pw.spec.ts

# Run headless
PLAYWRIGHT_HEADLESS=1 yarn test:e2e:playwright:chrome test/e2e/tests/settings/terms-of-use.pw.spec.ts

# Debug with the Playwright Inspector (step through each driver action)
PWDEBUG=1 yarn test:e2e:playwright:chrome test/e2e/tests/settings/terms-of-use.pw.spec.ts

Running E2E tests with feature flags

Feature flags used in tests fall into two categories: remote flags (runtime values fetched from client-config) and build-time flags (compile-time values set during the build). Use the workflow that matches the flag type.

Remote feature flags (runtime)

Remote flags are provided at runtime and should usually follow production defaults from the Feature Flag Registry. You do not need a custom build just to change a remote flag value for a test.

Use one of these test-time overrides:

• manifestFlags in withFixtures — best for simple, test-wide flag overrides that don't depend on other fixture state.
• FixtureBuilder.withRemoteFeatureFlags() — best when you need the flag change to interact with other fixture state. Note: this method is only available on the legacy FixtureBuilder; use this builder when you need it, even for new tests.

For code examples and detailed guidelines, see Feature flags in E2E tests in contributor-docs.

Build-time feature flags (compile-time)

Build-time flags are set before running tests and require creating a test build with the flag enabled. Set the flag either in your local .metamaskrc file or as an environment variable prefix (e.g. MULTICHAIN=1 yarn build:test), then follow the steps in Preparing a Test Build to create and run the build.

Feature Flag Registry

The Feature Flag Registry is the central source of truth for all remote feature flags used in MetaMask Extension E2E tests. A CI check runs on every PR to verify that every remote flag reference in changed files exists in the registry. For background on how remote feature flags work in MetaMask, see the Remote Feature Flags contributor doc.

Registry entry format

Each entry in test/e2e/feature-flags/feature-flag-registry.ts has the following shape:

myNewFlag: {
  name: 'myNewFlag',
  type: FeatureFlagType.Remote,
  inProd: true,
  productionDefault: false,
  status: FeatureFlagStatus.Active,
},

Add a flag to the registry

For the full process of creating a remote feature flag (LaunchDarkly setup, code integration), see the Remote Feature Flags contributor doc. Once the flag exists, register it for E2E tests:

1. Look up the flag's current production value from the client-config API. If the flag is not yet in production, set inProd: false and productionDefault to the intended default.
2. Add an entry to test/e2e/feature-flags/feature-flag-registry.ts in alphabetical order.
3. If you access the flag via a constant (e.g. remoteFeatureFlags[MY_CONSTANT]), also add the constant mapping to .github/scripts/known-feature-flag-constants.mts so the CI check can resolve it.

Override flags in E2E tests

To test behavior with a flag value different from the production default, see the override examples in Remote feature flags (runtime) above.

The registry module also exports helper functions for use in tests and tooling (e.g. getProductionRemoteFlagApiResponse(), getProductionRemoteFlagDefaults()). See the JSDoc in feature-flag-registry.ts for details.

Remove a flag

When a remote feature flag is fully rolled out or no longer needed:

1. Remove all references to the flag from application code (app/, ui/, shared/).
2. Either remove the entry from the registry, or change its status to FeatureFlagStatus.Deprecated if you want to track it temporarily.
3. The CI check will post a warning on PRs that remove the last codebase reference to a registered flag, reminding you to clean up the registry.

Running E2E performance benchmarks

E2E performance benchmarks measure flow timings (onboarding, send, swap, asset details, etc.) and can be run locally or in CI. Use yarn test:e2e:benchmark with --preset <name> or a file path. See test/e2e/benchmarks/flows/README.md for presets and options.

Running specific builds types e2e test

Different build types have different e2e tests sets. In order to run them look in the package.json file. You will find:

    "test:e2e:chrome:snaps": "SELENIUM_BROWSER=chrome node test/e2e/run-all.js --snaps",
    "test:e2e:firefox": "SELENIUM_BROWSER=firefox node test/e2e/run-all.js",

Test and iterate on GitHub Actions more quickly

Running the full workflow on GitHub Actions can take 30 minutes or more, but there are ways to speed it up for faster iteration

• Automatic build reuse — CI automatically detects when a PR's build-affecting source files haven't changed compared to a prior run (on the same branch or the base branch). When a match is found, it reuses the existing build artifacts instead of rebuilding, saving ~4 minutes for the webpack builds. This happens transparently with no action needed from you.
  • [force-builds] in the last commit message, or a force-builds label on the PR — Forces fresh builds even when CI would otherwise reuse prior artifacts. Useful when you need to verify that builds work after changing only non-code files (CI configs, docs, etc.), or if the automatic system is making a mistake.
  • [skip-builds] in the last commit message, or a skip-builds label on the PR — Reuses builds from the most recent prior run without verifying the source hash. This is the fastest option for iterating on tests or non-build changes, but it blocks merging — you must remove the tag/label and push again before the PR can enter the merge queue.
• Automatic E2E skipping — CI automatically skips E2E tests when the PR's changes don't require them (e.g., docs-only, CI-only, or test-only changes with reused builds). You can override this in both directions:
  • [skip-e2e] in the last commit message, or a skip-e2e label on the PR — Forces E2E tests to be skipped regardless of what files changed.
  • [force-e2e] in the last commit message, or a force-e2e label on the PR — Forces E2E tests to run even when CI would otherwise skip them. Useful for CI-only PRs that modify E2E workflow files.
• [skip-unit] in the last commit message (command not working yet, coming soon) - Skips the unit test suite
• trigger-ci-* as the branch name - This allows you to run the CI workflow without attaching it to a PR. This is useful if you need to test some things that you know will never be merged. Please clean up after yourself when you're done, and delete the branch.

Changing dependencies

Whenever you change dependencies (adding, removing, or updating, either in package.json or yarn.lock), there are various files that must be kept up-to-date.

• yarn.lock:
  • Run yarn again after your changes to ensure yarn.lock has been properly updated.
  • Run yarn lint:lockfile:dedupe:fix to remove duplicate dependencies from the lockfile.
• The allow-scripts configuration in package.json
  • Run yarn allow-scripts auto to update the allow-scripts configuration automatically. This config determines whether the package's install/postinstall scripts are allowed to run. Review each new package to determine whether the install script needs to run or not, testing if necessary.
  • Unfortunately, yarn allow-scripts auto will behave inconsistently on different platforms. macOS and Windows users may see extraneous changes relating to optional dependencies.
• The LavaMoat policy files
  • If you are a MetaMask team member and your PR is on a repository branch, you can use the bot command @metamaskbot update-policies to ask the MetaMask bot to automatically update the policies for you.
  • If your PR is from a fork, you can ask a MetaMask team member to help with updating the policy files.
  • Manual update instructions: The tl;dr is to run yarn lavamoat:auto to update these files, but there can be devils in the details:
    • The webpack app LavaMoat policy files live under lavamoat/webpack/*/policy.json and are re-generated by yarn lavamoat:auto.
      • These should be regenerated whenever the production dependencies for the app change.
    • Whenever you regenerate a policy file, review the changes to determine whether the access granted to each package seems appropriate.
    • Unfortunately, yarn lavamoat:auto will behave inconsistently on different platforms. macOS and Windows users may see extraneous changes relating to optional dependencies.
    • If you keep getting policy failures even after regenerating the policy files, try regenerating the policies after a clean install by doing:
      • rm -rf node_modules/ && yarn && yarn lavamoat:auto
    • Keep in mind that any kind of dynamic import or dynamic use of globals may elude LavaMoat's static analysis. Refer to the LavaMoat documentation or ask for help if you run into any issues.
• The Attributions file
  • If you are a MetaMask team member and your PR is on a repository branch, you can use the bot command @metamaskbot update-attributions to ask the MetaMask bot to automatically update the attributions file for you.
  • Manual update: run yarn attributions:generate.

Architecture

• Visual of the controller hierarchy and dependencies as of summer 2022.
• Visual of the entire codebase.

Other Docs

• How to add a new translation to MetaMask
• Publishing Guide
• How to use the TREZOR emulator
• Developing on MetaMask
• How to generate a visualization of this repository's development
• How to add new confirmations
• Browser support guidelines

Dapp Developer Resources

• Extend MetaMask's features w/ MetaMask Snaps.
• Prompt your users to add and switch to a new network.
• Change the logo that appears when your dapp connects to MetaMask.