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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 16
    • If you are using nvm (recommended) running nvm use will automatically choose the right node version for you.
  • Install Yarn v3
    • ONLY follow the steps in the "Install Corepack" and "Updating the global Yarn version" sections
    • DO NOT take any of the steps in the "Initializing your project", "Updating to the latest versions" or "Installing the latest build fresh from master" sections. These steps could result in your repo being reset or installing the wrong yarn version, which can break your build.
  • Duplicate .metamaskrc.dist within the root and rename it to .metamaskrc
  • 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.

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.


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, targetting 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]

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

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. 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

Dapp Developer Resources