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A modular wallet is a Modular Smart Contract Account (MSCA) controlled by a passkey. Modules can extend the wallet, for example to restrict transfers to an onchain allowlist.

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Passkeys

A passkey is the default signer for a modular wallet. It uses the WebAuthn standard. The key pair is generated on the user’s device and stored in a secure enclave or password manager. The user signs with biometrics or device unlock. No seed phrase or password. What to know:
  • Passkeys use the secp256r1 curve. Each signature includes WebAuthn metadata.
  • The key never leaves the user’s device. Your app can’t read it, Circle can’t read it, and it can’t be phished.
  • The modular wallets SDKs handle passkey login and signing through webAuthnAccount.
  • When the user signs, the SDK submits the signed user operation to a bundler, which broadcasts it onchain. Gas can be sponsored through Gas Station with paymaster: true.
Need an EOA-based signer instead of a passkey, for example when your app already uses a third-party auth provider like Dynamic to manage user identity? See Dynamic integration for the pattern.

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Backup and recovery

Passkeys replace traditional private keys, so backup matters. Synced passkeys (through Apple iCloud Keychain or Google Password Manager) restore on any device the user signs into. Device-bound passkeys like YubiKey do not sync. Losing that device means losing access unless the user has another credential. Circle adds recovery keys as a backup. A recovery key has the same permissions as a passkey. It uses ECDSA signatures and is self-custodial. No central authority can restore it. Users can register multiple recovery keys.
The passkey and any recovery keys are the only ways to access a modular wallet. Neither Circle nor your application can recover user wallets if every credential is lost.
For implementation details, see How to set up passkey recovery.

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Modules

Modules are contracts that extend a modular wallet’s behavior at runtime. They add capabilities or enforce rules the base wallet lacks. What to know:
  • Modules follow the ERC-6900 standard, which defines how MSCAs plug in optional logic.
  • Every modular wallet starts with the passkey signer as a built-in module. You attach more modules to extend behavior.
  • You can also build custom modules against the ERC-6900 standard to fit application-specific logic.

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Supported modules

ModuleDescriptionModule address
Passkey (WebAuthn)Default signer for the modular wallet. Built in.Built-in
Address BookRestricts transfers (ERC-20, ERC-721, ERC-1155) to a list of onchain-allowlisted addresses. Useful for treasury vaults that should only send to known counterparties.Mainnet and testnet: 0x0000000d81083B16EA76dfab46B0315B0eDBF3d0