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Snaps files

If you look at the directory structure of the Snaps monorepo project generated in the Snaps quickstart, it looks something like this:

your-snap-name/
├─ packages/
│  ├─ site/
|  |  |- src/
|  |  |  |- App.tsx
|  |  ├─ package.json
|  |  |- ...(react app content)
|  |
│  ├─ snap/
|  |  ├─ src/
|  |  |  |- index.ts
|  |  ├─ snap.manifest.json
|  |  ├─ package.json
|  |  |- ... (Snap content)
├─ package.json
├─ ... (other stuff)

The snap folder contains the Snap implementation, and the site folder contains the Snap companion dapp implementation.

This page examines the following Snap project files:

Manifest file​

To get MetaMask to execute your Snap, you must have a valid manifest file named snap.manifest.json, located in your package root directory. The manifest file of Hello World would look something like this:

snap.manifest.json
{
  "version": "1.0.0",
  "proposedName": "Hello World",
  "description": "A Snap that says hello!",
  "repository": {
    "type": "git",
    "url": "https://github.com/Hello/hello-snap.git"
  },
  "source": {
    "shasum": "w3FltkDjKQZiPwM+AThnmypt0OFF7hj4ycg/kxxv+nU=",
    "location": {
      "npm": {
        "filePath": "dist/bundle.js",
        "iconPath": "images/icon.svg",
        "packageName": "hello-snap",
        "registry": "https://registry.npmjs.org/"
      }
    }
  },
  "initialPermissions": {},
  "manifestVersion": "0.1"
}

The manifest tells MetaMask important information about your Snap, such as where it's published (using source.location), how to verify the integrity of the Snap source code (by attempting to reproduce the source.shasum value), and what permissions the Snap requests (using initialPermissions).

You might need to modify some manifest fields manually. For example, if you change the location of the icon SVG file, you must update source.location.npm.iconPath to match. You can also use the Snaps CLI to update some fields for you. For example, running yarn mm-snap build or yarn mm-snap manifest --fix updates source.shasum.

important

Some manifest fields must match the corresponding fields of the /snap/package.json file.

When updating the version and repository fields, the Snap inherits the values from package.json and overwrites them in snap.manifest.json. We recommend updating version and repository in package.json first, then building the Snap project.

The Snaps publishing specification details the requirements of both snap.manifest.json and its relationship to package.json.

note

Currently, Snaps can only be published to the official npm registry. In the future, developers will be able to distribute Snaps in different ways, and the manifest will expand to support different publishing solutions.

Configuration file​

The Snap configuration file, snap.config.js or snap.config.ts, must be placed in the project root directory. You can override the default values of the Snaps configuration options by specifying them in the configuration file. For example:

snap.config.js
module.exports = {
  input: "src/index.js",
  output: {
    path: "dist",
  },
  server: {
    port: 9000,
  },
}
note

You should not publish the configuration file to npm, since it's only used for development and building. However, you can commit the file to GitHub to share the configuration with your team, since it shouldn't contain any secrets.

Bundle file​

Because of the way Snaps are executed, they must be published as a single .js file containing the entire source code and all dependencies. Moreover, the Snaps execution environment has no DOM, no Node.js APIs, and no filesystem access, so anything that relies on the DOM doesn't work, and any Node built-ins must be bundled along with the Snap.

Running yarn start bundles your Snap for you.

You can also run yarn mm-snap build to bundle your Snap using webpack. This command finds all dependencies using your specified main entry point and outputs a bundle file to your specified output path.

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