eth_estimateGas - Flashblocks

Example code for the eth_estimateGas - Flashblocks method. Complete guide on how to use eth_estimateGas - Flashblocks in GetBlock Web3 documentation.

This estimates the gas needed to execute a transaction without submitting it. When called with "pending", the estimate is computed against state including preconfirmed transactions in the latest Flashblock — giving more accurate estimates for transactions that depend on state changes happening in the current block.

Parameters

Parameter	Type	Required	Description
callObject	object	Yes	Same shape as eth_call parameters
block	QUANTITY	No	"pending" for gas estimate against preconfirmed state (default is "latest")

Request Example

cURL

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "eth_estimateGas",
    "params": [
        {
            "from": "0x7a25d0f0Ff6a25f36De0a19C3d5f6dC2C6EAeD6a",
            "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
            "data": "0xa9059cbb0000000000000000000000007a25d0f0ff6a25f36de0a19c3d5f6dc2c6eaed6a00000000000000000000000000000000000000000000000000000000000186a0"
        },
        "pending"
    ],
    "id": "getblock.io"
}'

JavaScript (Axios)

import axios from 'axios';

const data = JSON.stringify({
    "jsonrpc": "2.0",
    "method": "eth_estimateGas",
    "params": [
        {
            "from": "0x7a25d0f0Ff6a25f36De0a19C3d5f6dC2C6EAeD6a",
            "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
            "data": "0xa9059cbb0000000000000000000000007a25d0f0ff6a25f36de0a19c3d5f6dc2c6eaed6a00000000000000000000000000000000000000000000000000000000000186a0"
        },
        "pending"
    ],
    "id": "getblock.io"
});

const config = {
    method: 'post',
    url: 'https://go.getblock.io/<ACCESS-TOKEN>/',
    headers: {
        'Content-Type': 'application/json'
    },
    data: data
};

axios(config)
    .then(response => console.log(JSON.stringify(response.data, null, 2)))
    .catch(error => console.log(error));

Python (Requests)

import requests
import json

url = "https://go.getblock.io/<ACCESS-TOKEN>/"

payload = json.dumps({
    "jsonrpc": "2.0",
    "method": "eth_estimateGas",
    "params": [
        {
            "from": "0x7a25d0f0Ff6a25f36De0a19C3d5f6dC2C6EAeD6a",
            "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
            "data": "0xa9059cbb0000000000000000000000007a25d0f0ff6a25f36de0a19c3d5f6dc2c6eaed6a00000000000000000000000000000000000000000000000000000000000186a0"
        },
        "pending"
    ],
    "id": "getblock.io"
})

headers = {
    'Content-Type': 'application/json'
}

response = requests.post(url, headers=headers, data=payload)
print(response.text)

Rust (Reqwest)

use reqwest::Client;
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();

    let payload = json!({
        "jsonrpc": "2.0",
        "method": "eth_estimateGas",
        "params": [
                {
                        "from": "0x7a25d0f0Ff6a25f36De0a19C3d5f6dC2C6EAeD6a",
                        "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
                        "data": "0xa9059cbb0000000000000000000000007a25d0f0ff6a25f36de0a19c3d5f6dc2c6eaed6a00000000000000000000000000000000000000000000000000000000000186a0"
                },
                "pending"
        ],
        "id": "getblock.io"
});

    let response = client
        .post("https://go.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&payload)
        .send()
        .await?;

    let result: serde_json::Value = response.json().await?;
    println!("{:#?}", result);

    Ok(())
}

Response Example

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0xc350"
}

Response Parameters

Field	Type	Description
result	QUANTITY	Estimated gas units (hex)

Use Cases

• Accurate gas estimation for transactions that depend on preconfirmed state (e.g. sequential swaps in a bundle)

• Detecting transactions that would revert given preconfirmed state changes

• Wallet fee suggestion UIs with Flashblocks-aware accuracy

Error Handling

Status Code	Error Message	Cause
403	Forbidden	Missing or invalid <ACCESS-TOKEN>
-32602	Invalid params	Request parameters are missing or malformed
-32603	Internal error	Server-side error while processing the request
429	Too Many Requests	Rate limit exceeded for your plan
3	execution reverted	Transaction would revert against the preconfirmed state — estimation cannot complete

SDK Integration

ethers.js

import { ethers } from 'ethers';

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

// Generic JSON-RPC call — 'pending' returns Flashblocks-preconfirmed state:
const result = await provider.send('eth_estimateGas', [{"from": "0x7a25d0f0Ff6a25f36De0a19C3d5f6dC2C6EAeD6a", "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "data": "0xa9059cbb0000000000000000000000007a25d0f0ff6a25f36de0a19c3d5f6dc2c6eaed6a00000000000000000000000000000000000000000000000000000000000186a0"}, "pending"]);
console.log(result);

// Many standard methods have typed wrappers on ethers Provider that accept 'pending':
// provider.getBalance(addr, 'pending'), provider.getTransactionCount(addr, 'pending'), etc.

viem

import { createPublicClient, http } from 'viem';

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

// viem's read methods accept blockTag: 'pending' for Flashblocks-preconfirmed state:
const result = await client.request({
    method: 'eth_estimateGas',
    params: [{"from": "0x7a25d0f0Ff6a25f36De0a19C3d5f6dC2C6EAeD6a", "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "data": "0xa9059cbb0000000000000000000000007a25d0f0ff6a25f36de0a19c3d5f6dc2c6eaed6a00000000000000000000000000000000000000000000000000000000000186a0"}, "pending"]
});
console.log(result);

// Typed wrappers also accept blockTag: 'pending':
// client.getBalance({ address, blockTag: 'pending' })
// client.getBlock({ blockTag: 'pending' })