RPC method

eth_subscribe on Polygon

Supported on SwiftNodes

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

newHeads	supported
First header after subscribing	1.5 s
Median gap between headers	1.5 s
Headers in 15 seconds	10
logs	supported
newPendingTransactions	supported

What this means on Polygon

Headers pushed over WebSocket are not identical to eth_getBlockByNumber over HTTP on Polygon. Only the HTTP block has size. 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/polygon?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/polygon?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 Polygon

eth_subscribe on other chains

Frequently asked questions

Does Polygon support eth_subscribe?

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

Does Polygon support WebSocket subscriptions?

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

Can I watch the Polygon mempool?

newPendingTransactions is supported.

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

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