eth_simulateV1 - Ethereum

Example code for the eth_simulateV1 JSON RPC method. Сomplete guide on how to use eth_simulateV1 JSON RPC in GetBlock Web3 documentation.

This method simulates a bundle of transactions against a specific block state and returns per-transaction execution results including gas used, return data, and event logs. Unlike eth_call (single message call) or eth_estimateGas (single-transaction gas), it simulates chained transactions in a single call. Used heavily by wallets, MEV searchers, and bundlers to preview complex multi-step operations before submission.

Parameters

Parameter	Type	Required	Description
payload	object	Yes	Simulation payload (see below)
blockParameter	string	Yes	Block state to simulate against — hex block number, or latest, finalized, safe

Payload Object

Field	Type	Required	Description
blockStateCalls	array of object	Yes	Ordered list of block simulations, each containing transactions to execute
traceTransfers	boolean	No	If true, emit synthetic Transfer events for ETH movements
validation	boolean	No	If true, apply signature and nonce validation (defaults to false)
returnFullTransactions	boolean	No	If true, return full transaction objects in the response

Block State Call Object

Field	Type	Required	Description
blockOverrides	object	No	Overrides for block-level fields (number, time, baseFeePerGas, etc.)
stateOverrides	object	No	Overrides for account state (balance, nonce, code, storage)
calls	array of object	Yes	Transactions to execute in this simulated block (same shape as eth_call transaction object)

Request

cURL

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "eth_simulateV1",
    "params": [
        {
            "blockStateCalls": [
                {
                    "calls": [
                        {
                            "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
                            "to": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
                            "data": "0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045"
                        }
                    ]
                }
            ],
            "validation": false,
            "traceTransfers": true
        },
        "latest"
    ],
    "id": "getblock.io"
}'

Axios

example.js

const axios = require('axios');

const response = await axios.post('https://go.getblock.io/<ACCESS-TOKEN>/', {
    jsonrpc: '2.0',
    method: 'eth_simulateV1',
    params: [
        {
            "blockStateCalls": [
                {
                    "calls": [
                        {
                            "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
                            "to": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
                            "data": "0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045"
                        }
                    ]
                }
            ],
            "validation": false,
            "traceTransfers": true
        },
        "latest"
    ],
    id: 'getblock.io'
}, {
    headers: { 'Content-Type': 'application/json' }
});

console.log(response.data.result);

Request

example.py

import requests

response = requests.post(
    'https://go.getblock.io/<ACCESS-TOKEN>/',
    headers={'Content-Type': 'application/json'},
    json={
        'jsonrpc': '2.0',
        'method': 'eth_simulateV1',
        'params': [
        {
            "blockStateCalls": [
                {
                    "calls": [
                        {
                            "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
                            "to": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
                            "data": "0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045"
                        }
                    ]
                }
            ],
            "validation": false,
            "traceTransfers": true
        },
        "latest"
    ],
        'id': 'getblock.io'
    }
)

print(response.json())

Rust

example.rs

use reqwest::Client;
use serde_json::{json, Value};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();
    
    let response = client
        .post("https://go.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&json!({
            "jsonrpc": "2.0",
            "method": "eth_simulateV1",
            "params": [
        {
            "blockStateCalls": [
                {
                    "calls": [
                        {
                            "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
                            "to": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
                            "data": "0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045"
                        }
                    ]
                }
            ],
            "validation": false,
            "traceTransfers": true
        },
        "latest"
    ],
            "id": "getblock.io"
        }))
        .send()
        .await?
        .json::<Value>()
        .await?;
    
    println!("Result: {}", response["result"]);
    Ok(())
}

Response

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": [
        {
            "number": "0x1720340",
            "hash": "0x9ec8e2f6b78d8f5f2ac3e5d61b0d38d4d5a8f0e7c8b5a2f9d3e6c1b7a4d0f2e5c",
            "timestamp": "0x67abcdef",
            "gasLimit": "0x39dc7fb",
            "gasUsed": "0x8ba0",
            "baseFeePerGas": "0x5f5e100",
            "calls": [
                {
                    "status": "0x1",
                    "returnData": "0x0000000000000000000000000000000000000000000000000de0b6b3a7640000",
                    "gasUsed": "0x8ba0",
                    "logs": []
                }
            ]
        }
    ]
}

Response Parameters

Parameter	Type	Description
jsonrpc	string	JSON-RPC protocol version ("2.0")
id	string	Request identifier matching the request
result	array of object	Simulated blocks, one per blockStateCall entry
result[].number	string	Simulated block number (hex)
result[].hash	string	Simulated block hash
result[].timestamp	string	Simulated block timestamp
result[].gasUsed	string	Total gas consumed by all calls in this simulated block
result[].baseFeePerGas	string	Base fee per gas for this simulated block
result[].calls	array of object	Per-call execution results
result[].calls[].status	string	0x1 = success, 0x0 = reverted
result[].calls[].returnData	string	Hex-encoded return data (or revert reason for reverted calls)
result[].calls[].gasUsed	string	Gas consumed by this call
result[].calls[].logs	array of object	Event logs emitted during this call

Use Cases

• Multi-Step Transaction Preview: Preview the outcome of a swap, approve+swap, or multi-hop DeFi operation before broadcasting

• MEV Bundle Simulation: Simulate an entire MEV bundle to verify profitability and behavior before submission to a builder

• Wallet UX Preview: Show users a rich 'this is what will happen' preview covering multiple contract interactions

• Account Abstraction Preflight: ERC-4337 bundlers and paymasters simulate UserOperations before submission

• What-If Analysis: State-overrides enable simulating actions with hypothetical account balances or contract code

Error Handling

Error Code	Message	Description
-32602	Invalid params	Payload structure is malformed or a call object is invalid
3	Execution reverted	One or more simulated calls reverted (individual calls[].status = "0x0" also indicates per-call reverts)
-32000	Execution error	Node failed to simulate the payload

Web3 Integration

Ethers.js

ethers-example.js

import { ethers } from 'ethers';

const provider = new ethers.JsonRpcProvider('https://go.getblock.io/<ACCESS-TOKEN>/');

const result = await provider.send('eth_simulateV1', [
    {
        blockStateCalls: [{
            calls: [{
                from: '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045',
                to: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
                data: '0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045',
            }],
        }],
        traceTransfers: true,
    },
    'latest',
]);
const simCall = result[0].calls[0];
console.log('Status:', simCall.status === '0x1' ? 'success' : 'reverted');
console.log('Return:', simCall.returnData);
console.log('Gas used:', simCall.gasUsed);

Viem

viem-example.js

import { createPublicClient, http } from 'viem';
import { mainnet } from 'viem/chains';

const client = createPublicClient({
    chain: mainnet,
    transport: http('https://go.getblock.io/<ACCESS-TOKEN>/'),
});

const result = await client.request({
    method: 'eth_simulateV1',
    params: [
        {
            blockStateCalls: [{
                calls: [{
                    from: '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045',
                    to: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
                    data: '0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045',
                }],
            }],
            traceTransfers: true,
        },
        'latest',
    ],
});
console.log(result[0].calls[0]);