Smart Account (ERC-4337) UserOp Builder

How to use the Smart Account (ERC-4337) UserOp Builder

1. Pick v0.6 or v0.7 from the EntryPoint Version selector — the tool defaults to v0.7.
2. Fill in Sender, Nonce, Call Data, the three gas limit fields, and the two fee fields (in Gwei) — the tool is prefilled with a working example so all outputs render immediately.
3. If a field is invalid, an alert names the offending field and the output panels are hidden until it's fixed.
4. Open Factory (account deployment) (labeled Init Code (account deployment) in v0.6) only when this UserOperation deploys a new smart account; open Paymaster only when a paymaster sponsors gas. Leaving either closed/blank omits those fields from the built UserOperation.
5. In the UserOpHash panel, set the Chain ID and EntryPoint Address (defaults to the canonical address for whichever version is selected, and updates automatically when you switch versions unless you've typed a custom address) to compute the exact hash that would need to be signed.
6. Each panel has its own Copy button; the PackedUserOperation panel only appears for v0.7.

See it in action

This is exactly what the tool shows by default — EntryPoint v0.7, chain ID 1, and the built-in example values — so you can compare it directly against what your own browser renders with no fields changed:

Input (defaults, nothing edited): Nonce 0, Call Data 0xdeadbeef, Call Gas Limit 100000, Verification Gas Limit 70000, Pre-Verification Gas 50000, Max Fee Per Gas 2 Gwei, Max Priority Fee Per Gas 1 Gwei, Chain ID 1, plus the Sender and EntryPoint Address (v0.7's canonical address) below:

Sender:

0x1234567890AbcdEF1234567890aBcdef12345678

EntryPoint Address:

0x0000000071727De22E5E9d8BAf0edAc6f37da032

UserOperation JSON:

{
  "sender": "0x1234567890AbcdEF1234567890aBcdef12345678",
  "nonce": "0",
  "callData": "0xdeadbeef",
  "callGasLimit": "100000",
  "verificationGasLimit": "70000",
  "preVerificationGas": "50000",
  "maxFeePerGas": "2000000000",
  "maxPriorityFeePerGas": "1000000000",
  "signature": "0xababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababab"
}

UserOpHash:

0xeee1df9b42a4a16e9a1b39609365a044e56dfa3d3a9cc6e8cc6b602d3c95ae3d

With a factory and paymaster

The default above is the common case — an already-deployed account paying its own gas — so its Factory and Paymaster sections stay closed. Opening both and filling them in changes the built UserOperation, and is also the only way to see the PackedUserOperation panel populate fields beyond the defaults. Starting from the same input above, plus:

Factory Address:

0xfac700000000000000000000000000000000000f

Factory Data:

0xcafebabe

Paymaster Address:

0xed00000000000000000000000000000000000001

Paymaster Verification Gas Limit 50000, Paymaster Post-Op Gas Limit 20000, Paymaster Data:

0xfeedface

UserOperation JSON now carries both sets of fields:

{
  "sender": "0x1234567890AbcdEF1234567890aBcdef12345678",
  "nonce": "0",
  "callData": "0xdeadbeef",
  "callGasLimit": "100000",
  "verificationGasLimit": "70000",
  "preVerificationGas": "50000",
  "maxFeePerGas": "2000000000",
  "maxPriorityFeePerGas": "1000000000",
  "signature": "0xababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababab",
  "factory": "0xfac700000000000000000000000000000000000f",
  "factoryData": "0xcafebabe",
  "paymaster": "0xed00000000000000000000000000000000000001",
  "paymasterVerificationGasLimit": "50000",
  "paymasterPostOpGasLimit": "20000",
  "paymasterData": "0xfeedface"
}

PackedUserOperation shows exactly how those fields fold together — factory/factoryData concatenate into initCode, and paymaster/its two gas limits/paymasterData concatenate into paymasterAndData:

{
  "accountGasLimits": "0x00000000000000000000000000011170000000000000000000000000000186a0",
  "callData": "0xdeadbeef",
  "initCode": "0xfac700000000000000000000000000000000000fcafebabe",
  "gasFees": "0x0000000000000000000000003b9aca0000000000000000000000000077359400",
  "nonce": "0",
  "paymasterAndData": "0xed000000000000000000000000000000000000010000000000000000000000000000c35000000000000000000000000000004e20feedface",
  "preVerificationGas": "50000",
  "sender": "0x1234567890AbcdEF1234567890aBcdef12345678",
  "signature": "0xababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababab"
}

UserOpHash changes too, since it's computed over the packed data:

0x13391878b7ca848cde5ff7381b62647eb0c2556c036854581a23ffe707c5440e