# The MetaMask Build System

> _tl;dr_ `yarn dist` for prod, `yarn start` for local development

This directory contains the MetaMask build system, which is used to build the MetaMask Extension such that it can be used in a supported browser.
From the repository root, the build system entry file is located at `development/build/index.js`.

Several package scripts invoke the build system.
For example, `yarn start` creates a watched development build, and `yarn dist` creates a production build.
Some of these scripts applies `lavamoat` to the build system, and some do not.
For local development, building without `lavamoat` is faster and therefore preferable.

The build system is not a full-featured CLI, but rather a script that expects some command line arguments and environment variables.
For instructions regarding environment variables, see [the main repository readme](../../README.md#building-locally).

Here follows basic usage information for the build system.

```text
Usage: yarn build <entry-task> [options]

Commands:
  yarn build prod       Create an optimized build for production environments.

  yarn build dev        Create an unoptimized, live-reloaded build for local
                        development.

  yarn build test       Create an optimized build for running e2e tests.

  yarn build testDev    Create an unoptimized, live-reloaded build for running
                        e2e tests.

Options:
  --beta-version     If the build type is "beta", the beta version number.
                                                           [number] [default: 0]
  --build-type       The "type" of build to create. One of: "beta", "main"
                                                      [string] [default: "main"]
  --omit-lockdown    Whether to omit SES lockdown files from the extension
                     bundle. Useful when linking dependencies that are
                     incompatible with lockdown.
                                                      [boolean] [default: false]
  --skip-stats       Whether to refrain from logging build progress. Mostly used
                     internally.
                                                      [boolean] [default: false]
```