JSON-RPC WebSocket

Geth supports JSON-RPC over WebSocket on default port 8546, and WebSocket is the right transport for eth_subscribe event subscriptions such as newHeads and logs per Geth RPC docs.

{"jsonrpc":"2.0","id":1,"method":"eth_subscribe","params":["newHeads"]}

For contract logs, subscribe with an address and topic filter:

{"jsonrpc":"2.0","id":2,"method":"eth_subscribe","params":["logs",{"address":"0x1111111111111111111111111111111111111111","topics":["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]}]}

:::tip Reconnect rule Subscriptions are not durable. On disconnect, reconnect with exponential backoff, resubscribe, then backfill missed blocks with eth_getLogs from the last processed block plus one. :::

Use WebSocket for streaming; use HTTP for deterministic backfill and retries.