@metamask/snaps-cli

@metamask/snaps-cli

A CLI for developing MetaMask Snaps.

Installation

Use Node.js 12.11.0 or later. We recommend nvm for managing Node versions.

• yarn global add snaps-cli

Basic Usage

mkdir mySnap
cd mySnap
mm-snap init

MetaMask Snaps

MetaMask Snaps consist of two things: a JSON manifest and a JavaScript bundle. For a variety of reasons, we decided to follow npm conventions. Thus, the manifest file is simply package.json, with the following required standard fields:

• name
• version
• description
• main (relative path to source entry point, not the bundle)
• repository

In addition, we use the following, required custom fields:

• web3Wallet (object)
  • bundle (object)
    • local (string; relative path to bundle)
    • url (string; absolute URL to bundle)
      • Set to e.g. localhost:8081/dist/bundle.js for local development.
  • initialPermissions ({ string: object }; permissions to be requested on Snap installation)
    • See this interface for details.

If you exclude any required fields from package.json, your Snap may not work properly or install at all.

We recommend building your Snap using this tool. You can bundle your Snap using your own tools, but it must run in SES and only use the global APIs that MetaMask exposes at runtime. Although Snaps currently execute in the browser, some browser APIs are not available for snaps, and Snaps do not have DOM access.

Assumed Project Structure

This tool has default arguments assuming the following project structure:

 .
 |- index.js
 |- dist/
 |-- bundle.js
 |- ... (all other project files and folders)

Source files other than index.js are located through its imports. The defaults can be overwritten using the snap.config.json config file, see below.

Permissions

This module uses permissions as defined in rpc-cap, MetaMask's JSON RPC capabilities middleware. See examples in this repo for details.

Usage

Always use Node.js 12.11.0 or greater.

snap --help

Usage: snap <command> [options]

Commands:
  snap init      Initialize Snap package                     [aliases: i]
  snap build     Build Snap from source                      [aliases: b]
  snap eval      Attempt to evaluate Snap bundle in SES      [aliases: e]
  snap manifest  Validate project package.json as a Snap manifest
                                                                    [aliases: m]
  snap serve     Locally serve Snap file(s) for testing      [aliases: s]
  snap watch     Build Snap on change                        [aliases: w]

Options (build):
  --help, -h                      Show help                            [boolean]
  --src, -s                       Source file
                                       [string] [required] [default: "index.js"]
  --dist, -d                      Output directory
                                          [string] [required] [default: "dist/"]
  --outfileName, -n               Output file name
                                                 [string] [default: "bundle.js"]
  --sourceMaps                    Whether building outputs sourcemaps
                                                      [boolean] [default: false]
  --stripComments, --strip        Whether to remove code comments from bundle
                                                      [boolean] [default: false]
  --port, -p                      Local server port for testing
                                             [number] [required] [default: 8081]
  --eval, -e                      Attempt to evaluate Snap bundle in SES
                                                       [boolean] [default: true]
  --manifest, -m                  Validate project package.json as a Snap
                                  manifest             [boolean] [default: true]
  --populate                      Update Snap manifest properties of
                                  package.json         [boolean] [default: true]
  --verboseErrors, -v, --verbose  Display original errors
                                                      [boolean] [default: false]
  --suppressWarnings, -w          Suppress warnings   [boolean] [default: false]

Examples:
  snap init                            Initialize Snap package from
                                            scratch
  snap build -s index.js -d out        Build 'Snap.js' as
                                            './out/bundle.js'
  snap build -s index.js -d out -n     Build 'Snap.js' as
  Snap.js                                 './out/Snap.js'
  snap serve -r out                    Serve files in './out' on port 8080
  snap serve -r out -p 9000            Serve files in './out' on port 9000
  snap watch -s index.js -d out        Rebuild './out/bundle.js' on changes
                                            to files in 'index.js' parent and
                                            child directories

Usage Notes

• Commands
  • watch --src ... --dist ... rebuilds on all changes in the parent directory of src and its children except:
    • node_modules/
    • test/ and tests/
    • The specified dist directory
    • Dotfiles
  • serve --root ... --port ... serves the root directory on localhost:port
    • By default, root serves the current working directory: .
• Arguments
  • src, snap, and outfileName must be file paths when specified
  • dist and root must be directory paths when specified

Configuration File

snap.config.json can be placed in the project root directory. It should have string keys matching command arguments. Values become argument defaults, which can still be overriden on the command line. Example:

{
  "src": "lib",
  "dist": "out",
  "port": 9000
}