RPC method

eth_subscribe on Katana

Supported on SwiftNodes

Everything below was measured on 2026-10-13 by calling eth_subscribe on Katana 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 Katana: what we measured

newHeads	supported
First header after subscribing	369 ms
Median gap between headers	997 ms
Headers in 15 seconds	15
logs	supported
newPendingTransactions	supported

What this means on Katana

Headers pushed over WebSocket are not identical to eth_getBlockByNumber over HTTP on Katana. Only the HTTP block has 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/katana?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/katana?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 Katana

eth_subscribe on other chains

Frequently asked questions

Does Katana support eth_subscribe?

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

Does Katana support WebSocket subscriptions?

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

Can I watch the Katana mempool?

newPendingTransactions is supported.

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

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