Scopes (CAIP-2)

MetaMask Connect Multichain uses CAIP standards to identify chains, accounts, and sessions.

Traditional single-chain dapps identify networks with a numeric chain ID (for example, 1 for Ethereum Mainnet). That works within EVM ecosystems, but it does not generalize across ecosystems. Solana does not use numeric chain IDs, and a raw value like 1 is ambiguous without an ecosystem context.

Scopes solve this by providing a universal chain identifier for a chain or set of chains. When you connect to MetaMask, you pass an array of scopes to declare exactly which chains your dapp needs. When you call invokeMethod, you pass a scope to target the correct chain without switching netwoks.

Format and examples

A scope is a chain identifier in namespace:reference format, as defined by CAIP-2. It identifies a specific blockchain across any ecosystem.

• The namespace identifies the ecosystem or standard (for example, eip155 for EVM, solana for Solana).
• The reference identifies a specific chain within that namespace.

// Connect to Ethereum, Polygon, and Solana in a single call
await client.connect([
  'eip155:1',                                    // Ethereum Mainnet
  'eip155:137',                                  // Polygon Mainnet
  'solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp'     // Solana Mainnet
], [])

// Send an RPC request to a specific chain using its scope
const balance = await client.invokeMethod({
  scope: 'eip155:1',
  request: { method: 'eth_getBalance', params: ['0xab1...', 'latest'] }
})

Supported scopes

Ecosystem	Format	Examples
EVM	eip155:<chainId>	eip155:1 (Ethereum), eip155:59144 (Linea), eip155:137 (Polygon)
Solana	solana:<genesisHash>	solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp (Mainnet), solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1 (Devnet)

Common EVM scopes

Network	Scope
Ethereum Mainnet	eip155:1
Linea Mainnet	eip155:59144
Base Mainnet	eip155:8453
Polygon Mainnet	eip155:137
Arbitrum One	eip155:42161
Optimism	eip155:10
Sepolia testnet	eip155:11155111

Next steps

• Accounts: Learn how CAIP-10 account IDs extend scopes with addresses.
• Sessions: Learn how scopes and accounts are grouped into authorized connections.