eth_simulateV1 - GIWA

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

This method simulates one or more blocks of transactions against a base block, returning the resulting state changes, return values, and logs. It is used to preview multi-step interactions before broadcasting.

Parameters

Parameter	Type	Required	Description
payload	object	Yes	Simulation payload with blockStateCalls and options
blockParameter	string	Yes	Base block in hex, or "latest", "pending"

Payload Object

Field	Type	Required	Description
blockStateCalls	array	Yes	Array of block objects each containing calls and optional state overrides
validation	boolean	No	Whether to run full validation on each call
traceTransfers	boolean	No	Whether to emit synthetic transfer logs

Request

cURL

curl --location --request POST 'https://shared.ap-southeast-1.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "eth_simulateV1",
    "params": [{ "blockStateCalls": [{ "calls": [{ "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045", "to": "0x4200000000000000000000000000000000000006", "data": "0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045" }] }], "validation": true, "traceTransfers": true }, "latest"],
    "id": "getblock.io"
}'

Axios

example.js

const axios = require('axios');

const response = await axios.post('https://shared.ap-southeast-1.getblock.io/<ACCESS-TOKEN>/', {
    jsonrpc: '2.0',
    method: 'eth_simulateV1',
    params: [{ blockStateCalls: [{ calls: [{ from: '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045', to: '0x4200000000000000000000000000000000000006', data: '0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045' }] }], validation: true, 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://shared.ap-southeast-1.getblock.io/<ACCESS-TOKEN>/',
    headers={'Content-Type': 'application/json'},
    json={
        'jsonrpc': '2.0',
        'method': 'eth_simulateV1',
        'params': [{ 'blockStateCalls': [{ 'calls': [{ 'from': '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045', 'to': '0x4200000000000000000000000000000000000006', 'data': '0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045' }] }], 'validation': True, '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://shared.ap-southeast-1.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&json!({
            "jsonrpc": "2.0",
            "method": "eth_simulateV1",
            "params": [{ "blockStateCalls": [{ "calls": [{ "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045", "to": "0x4200000000000000000000000000000000000006", "data": "0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045" }] }], "validation": true, "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": "0x14b8a10",
            "calls": [
                {
                    "status": "0x1",
                    "returnData": "0x00",
                    "gasUsed": "0x5b8d",
                    "logs": []
                }
            ]
        }
    ]
}

Response Parameters

Parameter	Type	Description
jsonrpc	string	JSON-RPC protocol version ("2.0")
id	string	Request identifier matching the request
result	array	Per-simulated-block results with call outcomes

Use Cases

• Bundle Preview: Simulate a sequence of calls to preview outcomes

• State Overrides: Test calls against modified balances or storage

• Transfer Tracing: Capture synthetic transfer logs for value flows

• dApp Safety: Warn users about failing or unexpected results before signing

Error Handling

Error Code	Message	Description
-32602	Invalid params	Malformed simulation payload
-32000	Execution error	A simulated call failed during execution

Web3 Integration

Ethers.js

ethers-example.js

import { ethers } from 'ethers';

const provider = new ethers.JsonRpcProvider('https://shared.ap-southeast-1.getblock.io/<ACCESS-TOKEN>/');

const sim = await provider.send('eth_simulateV1', [payload, 'latest']);

Viem

viem-example.js

import { createPublicClient, http } from 'viem';

const client = createPublicClient({
  transport: http('https://shared.ap-southeast-1.getblock.io/<ACCESS-TOKEN>/')
});

const sim = await client.simulateBlocks({ blocks: payload.blockStateCalls });