eth_subscribe on Fantom
Everything below was measured on 2026-10-13 by calling eth_subscribe on Fantom 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 Fantom: what we measured
| newHeads | supported |
|---|---|
| First header after subscribing | 393 ms |
| Median gap between headers | 10.2 s |
| Headers in 15 seconds | 3 |
| logs | supported |
| newPendingTransactions | supported |
What this means on Fantom
Headers pushed over WebSocket are not identical to eth_getBlockByNumber over HTTP on Fantom. Only the HTTP block has epoch, size, timestampNano, totalDifficulty. Fetch the block over HTTP if you need those fields.
Headers arrived every 10.2 s, slower than the 3.8 s average block time: the upstream batches headers, so expect several blocks per message gap and use the block number, not the message count.
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/fantom?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/fantom?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 Fantom
- eth_blockNumberSupported
- eth_chainIdSupported
- eth_getBalanceSupported
- eth_getBlockByNumberSupported
- eth_getTransactionByHashSupported
- eth_getTransactionReceiptSupported
- eth_callSupported
- eth_estimateGasSupported
- eth_gasPriceSupported
- eth_maxPriorityFeePerGasSupported
- eth_sendRawTransactionSupported
- eth_getTransactionCountSupported
- eth_getCodeSupported
- eth_getLogsSupported
- eth_getBlockReceiptsSupported
- eth_feeHistorySupported
- eth_getProofSupported
- eth_createAccessListSupported
- debug_traceCallSupported
- trace_blockSupported
- trace_transactionSupported
eth_subscribe on other chains
- Ethereum
- Base
- Arbitrum
- Optimism
- Polygon
- BNB Smart Chain
- Avalanche
- Sonic
- Linea
- Scroll
- zkSync Era
- Blast
- Mantle
- Gnosis
- Celo
- Berachain
- Monad
- Unichain
- Kaia
- PulseChain
- World Chain
- Ronin
- Abstract
- ApeChain
- MegaETH
- Lisk
- Hemi
- X Layer
- BOB
- Plasma
- Fraxtal
- Zora
- Story
- Soneium
- Sei
- Hyperliquid
- Taiko
- Morph
- Ink
- Katana
- Ethereum Classic
- opBNB
- Mode
- Flare
- Core
- Chiliz
- Telos EVM
- Tempo
- Cronos
- Manta Pacific
- Shibarium
- Boba Network
- Arbitrum Nova
- Immutable zkEVM
Frequently asked questions
Does Fantom support eth_subscribe?
Yes. eth_subscribe answered on the SwiftNodes Fantom endpoint when our weekly probe called it through the customer path (2026-10-13).
Does Fantom support WebSocket subscriptions?
Yes. newHeads and logs worked through wss://rpc.swiftnodes.io/ws/fantom on 2026-10-13.
Can I watch the Fantom mempool?
newPendingTransactions is supported.
Fantom endpoints, live block height and WebSocket status are on the Fantom RPC page.
One key covers every chain we serve, and SwiftNodes has a free tier.