Connect to a Snap

Dapps can connect to Snaps designed to communicate with dapps. Dapps can use these Snaps to take advantage of new features enabled by Snaps. This is possible because Snaps can expose a custom JSON-RPC API.

Detect wallet

To connect to a Snap, dapps must first detect MetaMask in the user's browser. See the Wallet documentation on how to connect to MetaMask.

Detect MetaMask Flask

When developing your Snap, you might need to require MetaMask Flask in your dapp. We recommend detecting MetaMask Flask using the multi-wallet detection mechanism specified by EIP-6963. Alternatively, you can use the window.ethereum injected provider, but this might fail if the user is running multiple wallet extensions simultaneously.

To detect MetaMask Flask, you can add the following to window.onload:

EIP-6963 example

index.js

window.addEventListener("eip6963:announceProvider", (event) => {
  /* event.detail contains the discovered provider interface. */
  const providerDetail = event.detail

  /* providerDetail.info.rdns is the best way to distinguish a wallet extension. */
  if (providerDetail.info.rdns === "io.metamask.flask") {
    console.log("MetaMask Flask successfully detected!")
    // Now you can use Snaps!
  } else {
    console.error("Please install MetaMask Flask!")
  }
})

window.dispatchEvent(new Event("eip6963:requestProvider"))

Injected provider example

index.js

const provider = window.ethereum

const isFlask = (
  await provider?.request({ method: "web3_clientVersion" })
)?.includes("flask")

if (provider && isFlask) {
  console.log("MetaMask Flask successfully detected!")
  // Now you can use Snaps!
} else {
  console.error("Please install MetaMask Flask!", error)
}

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.

note

A Snap can grant a dapp an automatic connection, skipping the need for users to confirm a connection.

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": {
      // The permissions in the Snap's manifest file.
    },
    "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.

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:

index.ts

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": {
      // The permissions in the Snap's manifest file.
    },
    "version": "SNAP_VERSION"
  }
}