# pimlico\_simulateAssetChanges

`pimlico_simulateAssetChanges` is a Pimlico bundler method that simulates a user operation and returns the balance changes it would cause, without sending it.

:::warning
NOTICE: This page is still in draft and the API may change.
:::

:::note
This endpoint does not support v0.6 user operations.
:::

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

```json
{
    "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

1. `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
2. `entryPoint`: EntryPoint Address
3. `blockNumber` (optional): hex encoded block number to run the simulation at (defaults to latest)

## Response

```json
{
  "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

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

### ERC-20 Token Example

```typescript
{
  "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

```typescript
{
  "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

```typescript
{
  "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 |