Base Flashblocks

Flashblocks-specific RPC methods, WebSocket subscriptions, and the infrastructure stream schema for Base pre-confirmations.

Flashblocks deliver ~200ms transaction preconfirmations on Base by streaming partial blocks before the next full block is sealed. Each 2-second Base block is divided into ten Flashblocks streamed at 200ms intervals, exposing preconfirmed state through the standard JSON-RPC pending block tag.

Endpoints

Transport

URL

HTTP

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

WebSocket

wss://go.getblock.io/<ACCESS-TOKEN>/

The pending tag works over HTTP. Flashblocks subscriptions require the WebSocket endpoint.

Flashblocks-Aware Methods

Method

Usage

eth_getTransactionCount

Pass "pending" for a nonce that accounts for Flashblock transactions

eth_getStorageAt

Pass "pending" for storage at preconfirmed state

eth_getBalance

Pass "pending" for the balance at the latest Flashblock state

eth_getBlockByNumber

Pass "pending" to retrieve the current Flashblock

eth_getBlockReceipt

Pass "pending" to get receipts for all pre-confirmed transactions in the current Flashblock.

eth_getBlockTransactionCountByNumber

Pass "pending" to get the count of pre-confirmed transactions in the current Flashblock.

eth_estimateGas

Pass "pending" to estimate gas against preconfirmed state

eth_call

Pass "pending" to execute against preconfirmed state

eth_simulateV1

Simulates against the latest preconfirmed state

eth_getLogs

Pass "fromBlock": "pending" and "toBlock": "pending" to query logs from pre-confirmed transactions, updated every ~200ms.

eth_getCode

Pass "pending" for contract code at preconfirmed state

base_transactionStatus

Reports whether a transaction hash is present in the mempool

eth_subscribe

Opens a Flashblocks WebSocket subscription

eth_unsubscribe

Cancels an active Flashblocks subscription

Example

The example below reads the pending balance of the Base WETH contract 0x4200000000000000000000000000000000000006. Substitute any supported method and parameters; the "pending" tag is what selects Flashblock state.

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "eth_getBalance",
    "params": ["0x4200000000000000000000000000000000000006", "pending"],
    "id": "getblock.io"
}'

example.js

const axios = require('axios');

const response = await axios.post('https://go.getblock.io/<ACCESS-TOKEN>/', {
    jsonrpc: '2.0',
    method: 'eth_getBalance',
    params: ['0x4200000000000000000000000000000000000006', 'pending'],
    id: 'getblock.io'
}, {
    headers: { 'Content-Type': 'application/json' }
});

console.log(response.data.result);

example.py

import requests

response = requests.post(
    'https://go.getblock.io/<ACCESS-TOKEN>/',
    headers={'Content-Type': 'application/json'},
    json={
        'jsonrpc': '2.0',
        'method': 'eth_getBalance',
        'params': ['0x4200000000000000000000000000000000000006', 'pending'],
        'id': 'getblock.io'
    }
)

print(response.json())

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_getBalance",
            "params": ["0x4200000000000000000000000000000000000006", "pending"],
            "id": "getblock.io"
        }))
        .send()
        .await?
        .json::<Value>()
        .await?;

    println!("Result: {}", response["result"]);
    Ok(())
}

Response

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0x3bdf5275488a29a8a57c"
}

Use Cases

Instant UI Feedback: Update wallet and dApp interfaces the moment a transaction is preconfirmed, without waiting for a sealed block.
Responsive Swaps: Surface preconfirmed swap results on decentralized exchanges with sub-second latency.
Onchain Gaming: Reflect game state changes as soon as actions are included in a Flashblock.
Nonce Management: Use eth_getTransactionCount with pending to avoid nonce collisions when submitting transactions in rapid succession.
Preconfirmed Receipts: Poll eth_getTransactionReceipt on a 200ms interval to confirm inclusion at Flashblock cadence.

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Last updated 4 days ago

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