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Work with third-party Snaps

Some existing, third-party Snaps are designed to communicate with dapps. As a dapp developer, you can use these Snaps to take advantage of new features enabled by Snaps. This is possible because Snaps can expose a JSON-RPC API. Snaps can decide to make their API available to dapps by requesting the endowment:rpc permission.

Connect to a Snap​

Connect to a Snap by calling the wallet_requestSnaps method from your dapp. If a user doesn't have the Snap installed in their MetaMask wallet, MetaMask prompts the user to install the Snap. The following are different possible outcomes from calling wallet_requestSnaps.

User rejects the installation request​

If the user rejects the installation request, the call to wallet_requestSnaps throws the following error:

{ "code": 4001, "message": "User rejected the request." }

User approves the installation request​

If the user approves the installation request, the call to wallet_requestSnaps returns an object with the following shape:

{
    "SNAP_ID": {
        "blocked": false,
        "enabled": true,
        "id": "SNAP_ID",
        "initialPermissions": {
            // ...all the permissions in the Snap's manifest
        },
        "version": "SNAP_VERSION"
    }
}

Snap is already installed​

If the Snap is already installed, the call to wallet_requestSnaps returns the same object as for a new installation of the Snap, but the user won't see a confirmation pop-up asking them to install the Snap.

important

Snaps are installed into the MetaMask instance of each user. If a Snap stores data, that data is specific to that user's MetaMask instance. However, that data can be shared with multiple dapps. Do not assume that data stored by a Snap is unique to your dapp.

Determine whether a Snap is installed​

Determine whether a Snap is installed by calling the wallet_getSnaps method from your dapp. This method returns a list of only those Snaps that are connected to your current dapp.

The response is in the form of an object keyed by the ID of the Snap. Each value is a nested object with additional information, such as the version of the Snap that is installed.

note

wallet_getSnaps only returns the Snaps that are connected to your dapp. The user may have other Snaps installed that your dapp is not aware of.

The following example verifies whether a Snap with ID npm:super-snap is installed:

const snaps = await ethereum.request({
  method: 'wallet_getSnaps'
});

const isMySnapInstalled = Object.keys(snaps).includes('npm:super-snap');

If you need to work with a specific version of a Snap, you can instead iterate over Object.values(snaps), and use the id and version properties inside each object to determine whether the Snap is installed with the required version.

note

A user cannot install multiple versions of a Snap into a single MetaMask instance. You should avoid requiring a specific version of a Snap unless you absolutely need to. In most cases, you should request the latest version of the Snap and architect your dapp to be able to work with that version.

Reconnect to a Snap​

At any time, a user can open their MetaMask Snaps settings menu and see all the dapps connected to a Snap. From that menu they can revoke a dapp connection. If your dapp loses the connection to a Snap, you can reconnect by calling wallet_requestSnaps. Since the Snap is already installed, this returns a success response without MetaMask showing a pop-up. However, if the user has disabled the Snap, the response has enabled set to false for your SNAP_ID:

{
    "SNAP_ID": {
        "blocked": false,
        "enabled": false,
        "id": "SNAP_ID",
        "initialPermissions": {
            // ...all the permissions in the Snap's manifest
        },
        "version": "SNAP_VERSION"
    }
}