eth_chainId

Returns the chain ID (EIP-155) as a hex string. Wallets and libraries check it before signing, and the signature commits to it, so a transaction signed for one chain cannot be replayed on another.

The chain ID each chain returned, with net_version alongside. Where the two differ, sign with eth_chainId.

1 of 55 chains return a net_version different from the chain ID.

eth_chainId on 55 chains, measured

Measured 2026-10-13 by calling eth_chainId through the SwiftNodes endpoint for each chain, re-measured weekly. Each chain links to its own page with the full response and code.

Replace YOUR_API_KEY in the examples on each chain page with your SwiftNodes key (free tier available).