newFlashblockTransactions - Flashblocks

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

This subscribes to individual preconfirmed transactions as they land in Flashblocks. Each notification carries one transaction. Pass true as a second parameter to include full transaction objects with associated logs; omit or pass false to receive only transaction hashes. Lighter-weight than newFlashblocks when you only care about the transaction stream and not the full block state.

WebSocket-only method. This method requires the WebSocket transport at wss://go.getblock.io/<ACCESS-TOKEN>/. It will not work via HTTP POST. Preconfirmed events arrive at the Flashblock cadence — approximately every 200ms on Base, 250ms on Optimism.

Parameters

Parameter	Type	Required	Description
subscriptionType	string	Yes	Must be "newFlashblockTransactions"
includeFullObjects	boolean	No	true to receive full transaction objects with logs; false (default) for hashes only

Request Example

cURL

# WebSocket-only. Use wscat (or similar) to connect first:
wscat -c 'wss://go.getblock.io/<ACCESS-TOKEN>/'

# Then send:
{"jsonrpc": "2.0", "method": "eth_subscribe", "params": ["newFlashblockTransactions", true], "id": "getblock.io"}

JavaScript (Axios)

import WebSocket from 'ws';

const ws = new WebSocket('wss://go.getblock.io/<ACCESS-TOKEN>/');

ws.on('open', () => {
    ws.send(JSON.stringify({
    "jsonrpc": "2.0",
    "method": "eth_subscribe",
    "params": [
        "newFlashblockTransactions",
        true
    ],
    "id": "getblock.io"
}));
});

ws.on('message', (data) => {
    const msg = JSON.parse(data.toString());
    if (msg.method === 'eth_subscription') {
        // Preconfirmed data update
        console.log(msg.params.result);
    } else {
        // Subscription ID response
        console.log('Subscribed:', msg.result);
    }
});

Python (Requests)

import asyncio
import json
import websockets

async def main():
    async with websockets.connect('wss://go.getblock.io/<ACCESS-TOKEN>/') as ws:
        await ws.send(json.dumps({
    "jsonrpc": "2.0",
    "method": "eth_subscribe",
    "params": [
        "newFlashblockTransactions",
        true
    ],
    "id": "getblock.io"
}))
        async for message in ws:
            msg = json.loads(message)
            if msg.get('method') == 'eth_subscription':
                # Preconfirmed data update
                print(msg['params']['result'])
            else:
                # Subscription ID response
                print('Subscribed:', msg.get('result'))

asyncio.run(main())

Rust (Reqwest)

use tokio_tungstenite::connect_async;
use tokio_tungstenite::tungstenite::Message;
use serde_json::json;
use futures_util::{SinkExt, StreamExt};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let (mut ws_stream, _) = connect_async("wss://go.getblock.io/<ACCESS-TOKEN>/").await?;

    let payload = json!({
        "jsonrpc": "2.0",
        "method": "eth_subscribe",
        "params": [
                "newFlashblockTransactions",
                true
        ],
        "id": "getblock.io"
});
    ws_stream.send(Message::Text(payload.to_string())).await?;

    while let Some(msg) = ws_stream.next().await {
        println!("{:?}", msg?);
    }
    Ok(())
}

Response Example

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0x5c1de6a7b8c9d0e1f2a3b4c5d6e7f8a9"
}

Response Parameters

Field	Type	Description
result	string	Hex-encoded subscription ID. Each subsequent notification carries either a transaction hash (default) or a full transaction object with logs (true param)

Use Cases

• Wallet infrastructure watching for a specific user's transactions to preconfirm

• Transaction-level analytics without the overhead of full block payloads

• Building activity feeds for accounts with sub-second latency

• Front-running detection at the sub-block level

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
-32600	Invalid Request	Subscription called over HTTP; use WebSocket

SDK Integration

ethers.js

import { ethers } from 'ethers';

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

// Flashblocks subscription types aren't first-class in ethers — use the raw send interface:
const subscriptionId = await provider.send('eth_subscribe', ["newFlashblockTransactions", true]);
console.log('Subscribed:', subscriptionId);

// Listen for incoming events on the WebSocket transport
provider.websocket.addEventListener('message', (event) => {
    const msg = JSON.parse(event.data);
    if (msg.method === 'eth_subscription' && msg.params?.subscription === subscriptionId) {
        console.log('Flashblocks update:', msg.params.result);
    }
});

viem

import { createPublicClient, webSocket } from 'viem';

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

// Flashblocks subscription types use the raw request interface:
const subscriptionId = await client.request({
    method: 'eth_subscribe',
    params: ["newFlashblockTransactions", true]
});
console.log('Subscribed:', subscriptionId);