Build a sponsored UserOperation

POST /api/aa/build-userop

Builds an unsigned ERC-4337 v0.7 UserOperation for the given account and calls, with the EntryPoint nonce, factory initCode (when the account is not yet deployed), conservative gas limits, current fees, and a paymaster signature already attached. Returns the UserOperation and the userOpHash for the account owner to sign (EIP-191 personal_sign). Building is unprivileged; metering happens at submission against the owner.

Authentication

Send your API key in the api-key header.

Responses

Status	Description
200	The unsigned UserOperation + the hash to sign.

200 response

{
  "success": true,
  "data": {
    "userOp": {
      "sender": "0x9a7f\u2026",
      "nonce": "0x0",
      "callData": "0x\u2026",
      "callGasLimit": "0x\u2026",
      "verificationGasLimit": "0x\u2026",
      "preVerificationGas": "0x\u2026",
      "maxFeePerGas": "0x\u2026",
      "maxPriorityFeePerGas": "0x\u2026",
      "paymaster": "0xpay\u2026",
      "paymasterData": "0x\u2026",
      "signature": "0x"
    },
    "userOpHash": "0xabc\u2026",
    "entryPoint": "0x0000000071727De22E5E9d8BAf0edAc6f37da032"
  },
  "timestamp": "2026-07-31T00:00:00.000Z"
}