> For the complete documentation index, see [llms.txt](https://docs.getblock.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.getblock.io/flashblocks/flashblocks-api/pendinglogs-flashblocks.md). # pendingLogs - Flashblocks This Subscribes to contract event logs emitted by preconfirmed transactions — sub-block latency for on-chain events. Filter by contract address (single or array) and event topics (same format as `eth_getLogs`). This is the fastest way to react to on-chain events, up to \~1.8 seconds ahead of the standard `logs` subscription. {% hint style="warning" %} **WebSocket-only method.** This method requires the WebSocket transport at `wss://go.getblock.io//`. It will not work via HTTP POST. Preconfirmed events arrive at the Flashblocks cadence — approximately every 200ms on Base, 250ms on Optimism. {% endhint %} ## Parameters | Parameter | Type | Required | Description | | ---------------- | ------ | -------- | ------------------------------------------------------------------------------------------- | | subscriptionType | string | Yes | Must be `"pendingLogs"` | | filter | object | No | Filter object: `address` (single address or array), `topics` (same format as `eth_getLogs`) | ## Request Example {% tabs %} {% tab title="cURL" %} {% code overflow="wrap" %} ```bash # WebSocket-only. Use wscat (or similar) to connect first: wscat -c 'wss://go.getblock.io//' # Then send: {"jsonrpc": "2.0", "method": "eth_subscribe", "params": ["pendingLogs", {"address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "topics": ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]}], "id": "getblock.io"} ``` {% endcode %} {% endtab %} {% tab title="JavaScript (Axios)" %} ```javascript import WebSocket from 'ws'; const ws = new WebSocket('wss://go.getblock.io//'); ws.on('open', () => { ws.send(JSON.stringify({ "jsonrpc": "2.0", "method": "eth_subscribe", "params": [ "pendingLogs", { "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "topics": [ "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef" ] } ], "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); } }); ``` {% endtab %} {% tab title="Python (Requests)" %} ```python import asyncio import json import websockets async def main(): async with websockets.connect('wss://go.getblock.io//') as ws: await ws.send(json.dumps({ "jsonrpc": "2.0", "method": "eth_subscribe", "params": [ "pendingLogs", { "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "topics": [ "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef" ] } ], "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()) ``` {% endtab %} {% tab title="Rust (Reqwest)" %} ```rust 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> { let (mut ws_stream, _) = connect_async("wss://go.getblock.io//").await?; let payload = json!({ "jsonrpc": "2.0", "method": "eth_subscribe", "params": [ "pendingLogs", { "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "topics": [ "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef" ] } ], "id": "getblock.io" }); ws_stream.send(Message::Text(payload.to_string())).await?; while let Some(msg) = ws_stream.next().await { println!("{:?}", msg?); } Ok(()) } ``` {% endtab %} {% endtabs %} ## Response Example {% code overflow="wrap" %} ```json { "jsonrpc": "2.0", "id": "getblock.io", "result": "0x7e2ef8b9c0d1e2f3a4b5c6d7e8f9a0b1" } ``` {% endcode %} ## Response Parameters | Field | Type | Description | | ------ | ------ | ----------------------------------------------------------------------------------------------------------------------------------- | | result | string | Hex-encoded subscription ID. Each subsequent notification carries a Log object matching the filter, from a preconfirmed transaction | ## Use Cases * Real-time event indexers — the lowest-latency way to react to on-chain events * Trading bots watching for specific ERC-20 transfers, DEX swaps, or oracle updates * Liquidation bots watching for Aave/Compound account state changes * Social/gaming applications reacting to on-chain events with instant UX feedback ## Error Handling | Status Code | Error Message | Cause | | ----------- | ----------------- | ------------------------------------------------------------- | | 403 | Forbidden | Missing or invalid `` | | -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 | | -32602 | Invalid filter | Filter object malformed — check `address` and `topics` format | ## SDK Integration {% tabs %} {% tab title="ethers.js" %} {% code overflow="wrap" %} ```javascript import { ethers } from 'ethers'; const provider = new ethers.WebSocketProvider('wss://go.getblock.io//'); // Flashblocks subscription types aren't first-class in ethers — use the raw send interface: const subscriptionId = await provider.send('eth_subscribe', ["pendingLogs", {"address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "topics": ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]}]); 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); } }); ``` {% endcode %} {% endtab %} {% tab title="viem" %} {% code overflow="wrap" %} ```javascript import { createPublicClient, webSocket } from 'viem'; const client = createPublicClient({ transport: webSocket('wss://go.getblock.io//') }); // Flashblocks subscription types use the raw request interface: const subscriptionId = await client.request({ method: 'eth_subscribe', params: ["pendingLogs", {"address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "topics": ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]}] }); console.log('Subscribed:', subscriptionId); ``` {% endcode %} {% endtab %} {% endtabs %} --- # Agent Instructions This documentation is published with GitBook. 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