# alchemy_simulateUserOperationAssetChanges
> For the complete documentation index, see [llms.txt](/docs/llms.txt).
POST https://eth-mainnet.g.alchemy.com/v2/{apiKey}
Simulates userOperations and returns a list of asset changes.
The results provided by this method are based on the blockchain's state at the moment of simulation. Changes in the blockchain state, such as updates to contract variables or balances, can occur between the time of simulation and userOperation execution.
This could lead to different outcomes than predicted. For instance, if a userOperation's effect is conditional on the current state of a contract, and this state is altered before the transaction is executed, the final result may not match the simulation.
Please conside this potential variance when using the API.
Reference: https://www.alchemy.com/docs/wallets/api-reference/bundler-api/useroperation-simulation-endpoints/alchemy-simulate-user-operation-asset-changes
## Parameters
| Name | Type | Required | Description |
|------|------|----------|-------------|
| UserOperation | object | Yes | userOperation to simulate. The signature can be a [dummy value](/docs/reference/bundler-faqs#what-is-a-dummy-signature); it doesn't need to be valid. |
| entryPoint | string | Yes | `EntryPoint` to use for the simulation. This MUST be one of the EntryPoints returned by the `supportedEntryPoints` RPC call. |
| blockNumber | string | No | Optional block number in context of which the simulation should be executed. If not specified, the current block number is used. |
## Result
**Simulation Result** (object): Object containing simulated asset changes and any potential errors.
## Example
### Request
```json
{
"jsonrpc": "2.0",
"method": "alchemy_simulateUserOperationAssetChanges",
"params": [
{
"sender": "0xceb161d3e0B6d01bc0e87ECC27fF9f2E2eCDCD81",
"nonce": "0x3",
"initCode": "0x",
"callData": "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",
"callGasLimit": "0x7A1200",
"verificationGasLimit": "0x927C0",
"preVerificationGas": "0x15F90",
"maxFeePerGas": "0x656703D00",
"maxPriorityFeePerGas": "0x13AB6680",
"signature": "0xfffffffffffffffffffffffffffffff0000000000000000000000000000000007aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa1c",
"paymasterAndData": "0x9db7f05b0eb93eb242b5913596dcfaada756af5c"
},
"0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789",
"0x113CF6E"
],
"id": 1
}
```
## Code Examples
### cURL
```bash
curl --request POST \
--url https://eth-mainnet.g.alchemy.com/v2/docs-demo \
--header 'Content-Type: application/json' \
--data '{
"jsonrpc": "2.0",
"id": 1,
"method": "alchemy_simulateUserOperationAssetChanges",
"params": [
{
"sender": "string",
"nonce": "string",
"initCode": "string",
"callData": "string",
"callGasLimit": "string",
"verificationGasLimit": "string",
"preVerificationGas": "string",
"maxFeePerGas": "string",
"maxPriorityFeePerGas": "string",
"signature": "string",
"paymasterAndData": "string",
"eip7702Auth": {
"chain_id": "string",
"address": "string",
"nonce": "string",
"y_parity": "string",
"r": "string",
"s": "string"
}
},
"0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789",
"0x113CF6E"
]
}'
```
### JavaScript
```javascript
const options = {
method: 'POST',
headers: {'Content-Type': 'application/json'},
body: JSON.stringify({
jsonrpc: '2.0',
id: 1,
method: 'alchemy_simulateUserOperationAssetChanges',
params: [
{
sender: 'string',
nonce: 'string',
initCode: 'string',
callData: 'string',
callGasLimit: 'string',
verificationGasLimit: 'string',
preVerificationGas: 'string',
maxFeePerGas: 'string',
maxPriorityFeePerGas: 'string',
signature: 'string',
paymasterAndData: 'string',
eip7702Auth: {
chain_id: 'string',
address: 'string',
nonce: 'string',
y_parity: 'string',
r: 'string',
s: 'string'
}
},
'0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789',
'0x113CF6E'
]
})
};
fetch('https://eth-mainnet.g.alchemy.com/v2/docs-demo', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));
```
### Python
```python
import requests
url = "https://eth-mainnet.g.alchemy.com/v2/docs-demo"
payload = {
"jsonrpc": "2.0",
"id": 1,
"method": "alchemy_simulateUserOperationAssetChanges",
"params": [
{
"sender": "string",
"nonce": "string",
"initCode": "string",
"callData": "string",
"callGasLimit": "string",
"verificationGasLimit": "string",
"preVerificationGas": "string",
"maxFeePerGas": "string",
"maxPriorityFeePerGas": "string",
"signature": "string",
"paymasterAndData": "string",
"eip7702Auth": {
"chain_id": "string",
"address": "string",
"nonce": "string",
"y_parity": "string",
"r": "string",
"s": "string"
}
},
"0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789",
"0x113CF6E"
]
}
headers = {"Content-Type": "application/json"}
response = requests.post(url, json=payload, headers=headers)
print(response.text)
```
### Go
```go
package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://eth-mainnet.g.alchemy.com/v2/docs-demo"
payload := strings.NewReader("{\n \"jsonrpc\": \"2.0\",\n \"id\": 1,\n \"method\": \"alchemy_simulateUserOperationAssetChanges\",\n \"params\": [\n {\n \"sender\": \"string\",\n \"nonce\": \"string\",\n \"initCode\": \"string\",\n \"callData\": \"string\",\n \"callGasLimit\": \"string\",\n \"verificationGasLimit\": \"string\",\n \"preVerificationGas\": \"string\",\n \"maxFeePerGas\": \"string\",\n \"maxPriorityFeePerGas\": \"string\",\n \"signature\": \"string\",\n \"paymasterAndData\": \"string\",\n \"eip7702Auth\": {\n \"chain_id\": \"string\",\n \"address\": \"string\",\n \"nonce\": \"string\",\n \"y_parity\": \"string\",\n \"r\": \"string\",\n \"s\": \"string\"\n }\n },\n \"0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789\",\n \"0x113CF6E\"\n ]\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}
```
### Java
```java
HttpResponse response = Unirest.post("https://eth-mainnet.g.alchemy.com/v2/docs-demo")
.header("Content-Type", "application/json")
.body("{\n \"jsonrpc\": \"2.0\",\n \"id\": 1,\n \"method\": \"alchemy_simulateUserOperationAssetChanges\",\n \"params\": [\n {\n \"sender\": \"string\",\n \"nonce\": \"string\",\n \"initCode\": \"string\",\n \"callData\": \"string\",\n \"callGasLimit\": \"string\",\n \"verificationGasLimit\": \"string\",\n \"preVerificationGas\": \"string\",\n \"maxFeePerGas\": \"string\",\n \"maxPriorityFeePerGas\": \"string\",\n \"signature\": \"string\",\n \"paymasterAndData\": \"string\",\n \"eip7702Auth\": {\n \"chain_id\": \"string\",\n \"address\": \"string\",\n \"nonce\": \"string\",\n \"y_parity\": \"string\",\n \"r\": \"string\",\n \"s\": \"string\"\n }\n },\n \"0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789\",\n \"0x113CF6E\"\n ]\n}")
.asString();
```
### C#
```csharp
using RestSharp;
var options = new RestClientOptions("https://eth-mainnet.g.alchemy.com/v2/docs-demo");
var client = new RestClient(options);
var request = new RestRequest("");
request.AddJsonBody("{\n \"jsonrpc\": \"2.0\",\n \"id\": 1,\n \"method\": \"alchemy_simulateUserOperationAssetChanges\",\n \"params\": [\n {\n \"sender\": \"string\",\n \"nonce\": \"string\",\n \"initCode\": \"string\",\n \"callData\": \"string\",\n \"callGasLimit\": \"string\",\n \"verificationGasLimit\": \"string\",\n \"preVerificationGas\": \"string\",\n \"maxFeePerGas\": \"string\",\n \"maxPriorityFeePerGas\": \"string\",\n \"signature\": \"string\",\n \"paymasterAndData\": \"string\",\n \"eip7702Auth\": {\n \"chain_id\": \"string\",\n \"address\": \"string\",\n \"nonce\": \"string\",\n \"y_parity\": \"string\",\n \"r\": \"string\",\n \"s\": \"string\"\n }\n },\n \"0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789\",\n \"0x113CF6E\"\n ]\n}", false);
var response = await client.PostAsync(request);
Console.WriteLine("{0}", response.Content);
```
## OpenRPC Method Specification
```yaml
name: alchemy_simulateUserOperationAssetChanges
description: |
Simulates userOperations and returns a list of asset changes.
The results provided by this method are based on the blockchain's state at the moment of simulation. Changes in the blockchain state, such as updates to contract variables or balances, can occur between the time of simulation and userOperation execution.
This could lead to different outcomes than predicted. For instance, if a userOperation's effect is conditional on the current state of a contract, and this state is altered before the transaction is executed, the final result may not match the simulation.
Please conside this potential variance when using the API.
params:
- name: UserOperation
required: true
description: userOperation to simulate. The signature can be a [dummy value](/docs/reference/bundler-faqs#what-is-a-dummy-signature); it doesn't need to be valid.
schema:
oneOf:
- type: object
title: User Operation v0.6
properties:
sender:
description: The account making the operation
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
nonce:
description: Anti-replay parameter; used as salt for first-time account creation
title: hex encoded unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]*|0)$
initCode:
description: The initCode of the account (needed if the account is not yet on-chain and needs creation)
title: hex encoded bytes
type: string
pattern: ^0x[0-9a-f]*$
callData:
description: Encoded data for the primary function call or operation
title: hex encoded bytes
type: string
pattern: ^0x[0-9a-f]*$
callGasLimit:
description: Gas allocated for the main execution call
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
verificationGasLimit:
description: Gas allocated for verification
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
preVerificationGas:
description: Gas for pre-verification execution and calldata
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
maxFeePerGas:
description: Maximum fee per gas (EIP-1559)
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
maxPriorityFeePerGas:
description: Max priority fee per gas (EIP-1559)
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
signature:
description: Data passed during verification
title: hex encoded bytes (any case)
type: string
pattern: ^0x[0-9a-fA-F]*$
paymasterAndData:
description: Paymaster address and extra data
title: hex encoded bytes
type: string
pattern: ^0x[0-9a-f]*$
eip7702Auth:
description: The authorization tuple that an EOA account delegates to in EIP-7702
title: Eip 7702 Auth
type: object
properties:
chain_id:
description: The chain Id of the authorization
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
address:
description: The address of the authorization
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
nonce:
description: The nonce for the authorization
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
y_parity:
description: Y parity of signed authorizzation tuple
title: hex encoded unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]*|0)$
r:
description: R of signed authorizzation tuple
title: hex encoded 256 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,31})|0$
s:
description: S of signed authorizzation tuple
title: hex encoded 256 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,31})|0$
- type: object
title: User Operation v0.7 / v0.8
properties:
sender:
description: Account initiating operation
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
nonce:
description: Account nonce or creation salt
title: hex encoded unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]*|0)$
callData:
description: Data for operation call
title: hex encoded bytes
type: string
pattern: ^0x[0-9a-f]*$
callGasLimit:
description: Gas allocated for call
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
verificationGasLimit:
description: Gas allocated for verification
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
maxFeePerGas:
description: Max fee per gas (EIP-1559)
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
maxPriorityFeePerGas:
description: Priority fee per gas (EIP-1559)
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
paymaster:
description: Paymaster contract address
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
paymasterData:
description: Data for paymaster
title: hex encoded bytes
type: string
pattern: ^0x[0-9a-f]*$
paymasterVerificationGasLimit:
type: string
description: The gas limit for paymaster verification.
factory:
description: The account factory address (needed if and only if the account is not yet on-chain and needs to be created)
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
factoryData:
description: Data for the account factory (only if the account factory exists)
title: hex encoded bytes
type: string
pattern: ^0x[0-9a-f]*$
preVerificationGas:
description: The amount of gas to pay for to compensate the bundler for pre-verification execution and calldata
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
paymasterPostOpGasLimit:
description: The amount of gas to allocate for the paymaster post-op code (only if a paymaster exists)
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
signature:
description: Data passed into the account along with the nonce during the verification step
title: hex encoded bytes (any case)
type: string
pattern: ^0x[0-9a-fA-F]*$
eip7702Auth:
description: The authorization tuple that an EOA account delegates to in EIP-7702
title: Eip 7702 Auth
type: object
properties:
chain_id:
description: The chain Id of the authorization
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
address:
description: The address of the authorization
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
nonce:
description: The nonce for the authorization
title: hex encoded 64 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,15})|0$
y_parity:
description: Y parity of signed authorizzation tuple
title: hex encoded unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]*|0)$
r:
description: R of signed authorizzation tuple
title: hex encoded 256 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,31})|0$
s:
description: S of signed authorizzation tuple
title: hex encoded 256 bit unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]{0,31})|0$
- name: entryPoint
required: true
description: '`EntryPoint` to use for the simulation. This MUST be one of the EntryPoints returned by the `supportedEntryPoints` RPC call.'
schema:
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
- name: blockNumber
required: false
description: Optional block number in context of which the simulation should be executed. If not specified, the current block number is used.
schema:
title: hex encoded unsigned integer
type: string
pattern: ^0x([1-9a-f]+[0-9a-f]*|0)$
result:
name: Simulation Result
description: Object containing simulated asset changes and any potential errors.
schema:
type: object
properties:
changes:
type: array
items:
type: object
required:
- assetType
- changeType
- from
- to
- rawAmount
- amount
- symbol
- decimals
- contractAddress
- name
- logo
- tokenId
properties:
assetType:
type: string
enum:
- NATIVE
- ERC20
- ERC721
- ERC1155
- SPECIAL_NFT
changeType:
type: string
enum:
- APPROVE
- TRANSFER
from:
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
description: address the transaction is sent from
to:
title: hex encoded address
type: string
pattern: ^0x[0-9a-fA-F]{40}$
description: address the transaction is directed to
rawAmount:
type: string
amount:
type: string
symbol:
type: string
decimals:
type:
- number
- 'null'
contractAddress:
type:
- string
- 'null'
name:
type:
- string
- 'null'
logo:
type:
- string
- 'null'
tokenId:
type:
- number
- 'null'
error:
type:
- object
- 'null'
properties:
message:
type: string
revertReason:
type: string
nullable: true
description: The reason why a transaction would revert. Provides details about potential transaction failure before execution.
examples:
- name: alchemy_simulateUserOperationAssetChanges example
params:
- name: UserOperation
value:
sender: '0xceb161d3e0B6d01bc0e87ECC27fF9f2E2eCDCD81'
nonce: '0x3'
initCode: 0x
callData: '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'
callGasLimit: '0x7A1200'
verificationGasLimit: '0x927C0'
preVerificationGas: '0x15F90'
maxFeePerGas: '0x656703D00'
maxPriorityFeePerGas: '0x13AB6680'
signature: '0xfffffffffffffffffffffffffffffff0000000000000000000000000000000007aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa1c'
paymasterAndData: '0x9db7f05b0eb93eb242b5913596dcfaada756af5c'
- name: entryPoint
value: '0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789'
- name: blockNumber
value: '0x113CF6E'
```