@metamask/snaps-cli v6.5.2
@metamask/snaps-cli
A CLI for developing MetaMask Snaps.
Installation
Use Node.js 16.0.0
or later.
We recommend nvm for managing Node.js versions.
Install a dev dependency in your snap project or globally using yarn
or npm
:
npm install -g @metamask/snaps-cli
yarn global add @metamask/snaps-cli
Usage
Usage: mm-snap <command> [options]
Commands:
mm-snap build Build Snap from source [aliases: b]
mm-snap eval Attempt to evaluate Snap bundle in SES [aliases: e]
mm-snap init [directory] Initialize Snap package [aliases: i]
mm-snap manifest Validate the snap.manifest.json file [aliases: m]
mm-snap serve Locally serve Snap file(s) for testing [aliases: s]
mm-snap watch Build Snap on change [aliases: w]
Options:
--version Show version number [boolean]
--verboseErrors Display original errors [boolean] [default: true]
--suppressWarnings Whether to suppress warnings[boolean] [default: false]
-h, --help Show help [boolean]
Examples:
mm-snap init Initialize a snap project in the
current directory
mm-snap init my-snap Initialize a snap project in the
'my-snap' directory
mm-snap build -s src/index.js -d out Build 'src/index.js' as
'./out/bundle.js'
mm-snap build -s src/index.js -d out -n Build 'src/index.js' as
snap.js './out/snap.js'
mm-snap serve -r out Serve files in './out' on port 8080
mm-snap serve -r out -p 9000 Serve files in './out' on port 9000
mm-snap watch -s src/index.js -d out Rebuild './out/bundle.js' on changes
to files in 'src/index.js' parent
and child directories
MetaMask Snaps
MetaMask Snaps enables trustlessly extending the functionality of MetaMask at runtime. A Snap consist of two things: a JSON manifest and a JavaScript bundle. At present, Snaps can be published as npm packages on the public npm registry, or hosted locally during development. In the future, it will be possible to publish snaps on many different platforms, including arbitrary npm registries and IPFS.
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 to Snaps, and Snaps do not have DOM access.
The Snap Manifest
Your manifest must be named snap.manifest.json
and located in the root directory of your npm package.
Here's an example manifest:
{
"version": "0.7.0",
"proposedName": "@metamask/template-snap",
"description": "A MetaMask Snap template.",
"repository": {
"type": "git",
"url": "https://github.com/MetaMask/template-snap.git"
},
"source": {
"shasum": "w3FltkDjKQZiPwM+AThnmypt0OFF7hj4ycg/kxxv+nU=",
"location": {
"npm": {
"filePath": "dist/bundle.js",
"iconPath": "images/icon.svg",
"packageName": "@metamask/template-snap",
"registry": "https://registry.npmjs.org/"
}
}
},
"initialPermissions": {
"snap_confirm": {}
},
"manifestVersion": "0.1"
}
Refer to the Snaps publishing specification and the manifest JSON schema for details.
ATTN: If your Snap is not compatible with the publishing specification, your Snap may not work properly or install at all.
Assumed Project Structure
This tool has default arguments assuming the following project structure:
snap-project/
├─ package.json
├─ src/
│ ├─ index.js
├─ snap.manifest.json
├─ 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.js
config file.
Configuration File
snap.config.js
should be placed in the project root directory. It can override cli options - the property cliOptions
should have string keys matching command arguments. Values become argument defaults, which can still be overridden on the command line.
Example:
module.exports = {
cliOptions: {
src: 'lib/index.js',
dist: 'out',
port: 9000,
},
};
If you want to customize the Browserify build process, you can provide bundlerCustomizer
property. It's a function that takes one argument - browserify object which we use internally to bundle the snap. You can transform it in any way you want, for example adding plugins.
Example:
const brfs = require('brfs');
module.exports = {
cliOptions: {
/* ... */
},
bundlerCustomizer: (bundler) => {
bundler.transform(brfs);
},
};
The configuration file should not be published.
Gotchas
- Commands
watch --src ... --dist ...
rebuilds on all changes in the parent directory ofsrc
and its children except:node_modules/
test/
,tests/
,**/*.test.js
, and**/*.test.ts
- The specified
dist
directory - Dotfiles
serve --root ... --port ...
serves theroot
directory onlocalhost:port
- By default,
root
serves the current working directory:.
- By default,
- Arguments
src
must be a file path when specifieddist
androot
must be directory paths when specifiedtranspilationMode
must be at leastlocalOnly
for TypeScript Snaps
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