Websockets

Chapter 21: WebSocket Connections

Overview

WebSockets provide persistent connections for real-time blockchain updates.

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21.1 Why WebSockets?

Feature	HTTP	WebSocket
Connection	Request-Response	Persistent
Latency	Higher	Lower
Real-time	Polling needed	Push-based
Use case	Queries	Live data

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21.2 Ethereum WebSocket

Connect

const ws = new WebSocket('ws://localhost:8546');

Subscribe to New Blocks

ws.onopen = () => {
  ws.send(JSON.stringify({
    jsonrpc: '2.0',
    method: 'eth_subscribe',
    params: ['newHeads'],
    id: 1
  }));
};

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  console.log('New block:', data.params.result);
};

Subscribe to Pending Transactions

ws.send(JSON.stringify({
  jsonrpc: '2.0',
  method: 'eth_subscribe',
  params: ['newPendingTransactions'],
  id: 2
}));

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21.3 WebSocket Flags

geth \
  --ws \
  --ws.addr 0.0.0.0 \
  --ws.port 8546 \
  --ws.api eth,net,web3 \
  --ws.origins "*" \
  --ws.ratelimit 500

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Summary

• WebSockets enable real-time updates
• Subscribe to new blocks, pending transactions
• Lower latency than HTTP polling

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Last Updated: 2026-02-20