metamask-extension icon indicating copy to clipboard operation
metamask-extension copied to clipboard

:globe_with_meridians: :electric_plug: The MetaMask browser extension enables browsing Ethereum blockchain enabled websites

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 our Twitter or Medium pages.

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

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

Building locally

  • Install Node.js version 20

    • 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.
  • Run yarn install to install the dependencies.

  • Build the project to the ./dist/ folder with yarn dist.

    • Optionally, you may run yarn start to run dev mode.
    • 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

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.


Development builds

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

React and Redux DevTools

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/

Running E2E Tests

Our e2e test suite can be run on either Firefox or Chrome.

  1. required yarn build:test to create a test build.
  2. run tests, targeting the browser:
  • Firefox e2e tests can be run with yarn test:e2e:firefox.
  • Chrome e2e tests can be run with yarn test:e2e:chrome. The chromedriver package major version must match the major version of your local Chrome installation. If they don't match, update whichever is behind before running Chrome e2e tests.

These test scripts all support additional options, which might be helpful for debugging. Run the script with the flag --help to see all options.

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 used; either 'chrome' or 'firefox'.
                                            [string] [choices: "chrome", "firefox"]
  --debug             Run tests in debug mode, logging each driver interaction
                                                         [boolean] [default: false]
  --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 (ganache, 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-details.spec.js --browser=chrome --debug --leave-running

Running specific builds types e2e test

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

    "test:e2e:chrome:mmi": "SELENIUM_BROWSER=chrome node test/e2e/run-all.js --mmi",
    "test:e2e:chrome:snaps": "SELENIUM_BROWSER=chrome node test/e2e/run-all.js --snaps",
    "test:e2e:chrome:mv3": "ENABLE_MV3=true SELENIUM_BROWSER=chrome node test/e2e/run-all.js",

Note: Running MMI e2e tests

When running e2e on an MMI build you need to know that there are 2 separated set of tests:

  • MMI runs a subset of MetaMask's e2e tests. To facilitate this, we have appended the @no-mmi tags to the names of those tests that are not applicable to this build type.
  • MMI runs another specific set of e2e legacy tests which are better documented here

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:
      • There are two sets of LavaMoat policy files:
        • The production LavaMoat policy files (lavamoat/browserify/*/policy.json), which are re-generated using yarn lavamoat:background:auto. Add --help for usage.
          • These should be regenerated whenever the production dependencies for the background change.
        • The build system LavaMoat policy file (lavamoat/build-system/policy.json), which is re-generated using yarn lavamoat:build:auto.
          • This should be regenerated whenever the dependencies used by the build system itself 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.


Architecture Diagram

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

Dapp Developer Resources