pimlico_simulateAssetChanges

This method shows asset changes that a user operation would produce if executed. It simulates the user operation and shows all balance changes including native currency, ERC-20, ERC-1155, and ERC-721 tokens.

Request

{
    "jsonrpc": "2.0",
    "method": "pimlico_simulateAssetChanges",
    "id": 4337,
    "params": [
        {
            "sender": "0x5a6b47F4131bf1feAFA56A05573314BcF44C9149",
            "nonce": "0x1",
            "callData": "0xe9ae5c53...",
            "callGasLimit": "0x0",
            "verificationGasLimit": "0x0",
            "preVerificationGas": "0x0",
            "maxFeePerGas": "0x7a5cf70d5",
            "maxPriorityFeePerGas": "0x3b9aca00",
            "paymasterVerificationGasLimit": "0x0",
            "paymasterPostOpGasLimit": "0x0",
            "signature": "0xfffffffffffffffffffffffffffffff0000000000000000000000000000000007aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa1c"
        },
        "0x0000000071727De22E5E9d8BAf0edAc6f37da032"
    ]
}

Parameters

userOperation: Expects the same userOperation format as eth_estimateUserOperationGas
- Signature must be a valid dummy signature
- Gas fields (callGasLimit, verificationGasLimit, preVerificationGas, paymasterPostOpGasLimit, paymasterVerificationGasLimit) are optional
- Gas price fields (maxFeePerGas, maxPriorityFeePerGas) are optional
entryPoint: EntryPoint Address
blockNumber (optional): hex encoded block number to run the simulation at (defaults to latest)

Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "assetChanges": [
      {
        "token": {
          "tokenType": "ERC-20",
          "address": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
          "decimals": 6,
          "name": "USD Coin",
          "symbol": "USDC"
        },
        "value": {
          "diff": "-1000000",
          "pre": "100000000",
          "post": "99000000"
        }
      },
      {
        "token": {
          "tokenType": "ERC-20",
          "address": "0x2260FAC5E5542a773Aa44fBCfeDf7C193bc2C599",
          "decimals": 8,
          "name": "Wrapped BTC",
          "symbol": "WBTC"
        },
        "value": {
          "diff": "1196",
          "pre": "0",
          "post": "1196"
        }
      },
      {
        "token": {
          "tokenType": "NATIVE"
        },
        "value": {
          "diff": "-1000000000000000000",
          "pre": "5000000000000000000",
          "post": "4000000000000000000"
        }
      }
    ]
  }
}

Response Format

Native Currency Example

{
  "token": {
    "tokenType": "NATIVE"
  },
  "value": {
    "diff": "String", // BigInt string
    "pre": "String",  // BigInt string
    "post": "String"  // BigInt string
  }
}

ERC-20 Token Example

{
  "token": {
    "tokenType": "ERC-20",
    "address": "Address",
    "decimals": "Number",
    "name": "String", // (Optional)
    "symbol": "String" // (Optional)
  },
  "value": {
    "diff": "String", // BigInt string
    "pre": "String",  // BigInt string
    "post": "String"  // BigInt string
  }
}

ERC-721 Token Example

{
  "token": {
    "tokenType": "ERC-721",
    "address": "Address",
    "tokenId": "Number",
    "name": "String", // (Optional)
    "symbol": "String" // (Optional)
  },
  "value": {
    "diff": "String", // BigInt string
    "pre": "String",  // BigInt string
    "post": "String"  // BigInt string
  }
}

ERC-1155 Token Example

{
  "token": {
    "tokenType": "ERC-1155",
    "address": "Address",
    "tokenId": "Number",
    "name": "String", // (Optional)
    "symbol": "String" // (Optional)
  },
  "value": {
    "diff": "String", // BigInt string
    "pre": "String",  // BigInt string
    "post": "String"  // BigInt string
  }
}

Token Metadata Fields

Metadata fields are included when available based on token type:

For ERC-20 tokens: name, symbol
For ERC-721 tokens: name, symbol
For ERC-1155 tokens: name, symbol

These fields will be included when they can be found, otherwise they'll be undefined. This is because metadata is optional in ERC-20, ERC-721, ERC-1155 standards, though most tokens do support these fields.

Error Responses

Error Code	Description
AA23	UserOperation reverted during simulation
UserOperationReverted	User operation execution failed during simulation
SimulateValidation	Validation failed for the user operation