RPC method

eth_subscribe on Core

Supported on SwiftNodes

Everything below was measured on 2026-10-13 by calling eth_subscribe on Core through the same endpoint customers use, and is re-measured weekly.

What eth_subscribe does

Opens a subscription over WebSocket: newHeads pushes each new block header, logs pushes matching events, and newPendingTransactions pushes mempool transaction hashes where the node exposes them. It replaces polling, and it only works over WebSocket, not HTTP.

eth_subscribe on Core: what we measured

newHeads	supported
First header after subscribing	2.4 s
Median gap between headers	3.0 s
Headers in 15 seconds	5
logs	supported
newPendingTransactions	supported

What this means on Core

Headers pushed over WebSocket are not identical to eth_getBlockByNumber over HTTP on Core. Only the HTTP block has milliTimestamp, size, totalDifficulty, withdrawals. Fetch the block over HTTP if you need those fields.

Subscriptions end when the connection drops. Reconnect with backoff and, after reconnecting, fetch the blocks you missed with eth_getBlockByNumber.

Example request

wscat -c "wss://rpc.swiftnodes.io/ws/core?key=YOUR_API_KEY"
> {"jsonrpc":"2.0","id":1,"method":"eth_subscribe","params":["newHeads"]}

import { createPublicClient, webSocket } from "viem";

const client = createPublicClient({
  transport: webSocket("wss://rpc.swiftnodes.io/ws/core?key=YOUR_API_KEY", { reconnect: true }),
});

const unwatch = client.watchBlocks({
  onBlock: (block) => console.log(block.number, block.hash),
});

// Events from one contract, pushed as they are mined
client.watchContractEvent({ address: token, abi: erc20Abi, eventName: "Transfer", onLogs: (logs) => console.log(logs) });

Other methods on Core

eth_subscribe on other chains

Frequently asked questions

Does Core support eth_subscribe?

Yes. eth_subscribe answered on the SwiftNodes Core endpoint when our weekly probe called it through the customer path (2026-10-13).

Does Core support WebSocket subscriptions?

Yes. newHeads and logs worked through wss://rpc.swiftnodes.io/ws/core on 2026-10-13.

Can I watch the Core mempool?

newPendingTransactions is supported.

Core endpoints, live block height and WebSocket status are on the Core RPC page.

One key covers every chain we serve, and SwiftNodes has a free tier.