Intermediate

What Is a Chain ID?

By DappAtlas editors ·

On this page

A chain ID is a number that uniquely identifies an EVM network, such as 1 for Ethereum or 8453 for Base. Wallets include it in every signed transaction so it cannot be replayed on another chain.

Key takeaways

  • Each EVM network has its own chain ID: 1 for Ethereum, 8453 for Base.
  • It is part of every signed transaction since EIP-155.
  • Wallets show it in decimal or hex (Base: 8453 or 0x2105).
  • A wrong chain ID when adding a network makes the wallet reject it.

Not to be confused with: rpc endpoint — the server URL you connect to; many endpoints can serve the same chain ID.

How a chain ID works

When you sign a transaction, the wallet mixes the chain ID into the signature. A node on another network sees a different chain ID and rejects the transaction, which prevents replay attacks.[1]

How a chain ID is used

You enter it when adding a network to a wallet by hand, and apps use it to check that your wallet is on the right network before you sign.

The Bottom Line

The chain ID tells wallets and nodes which network a transaction belongs to. Copy it from a trusted source when adding a network.

Educational content, not financial advice.

RPC endpointThe URL a wallet or app uses to talk to a blockchain node.Gas feeWhat you pay the network to process a transaction.
Pros
  • Stops transactions from being replayed on other chains
Cons
  • Copying the wrong ID from an unofficial list can connect you to a fake network
Sources (2)
  1. [1] Ethereum Improvement Proposals. “EIP-155: Simple replay attack protection.” Accessed Sep 26, 2026.
  2. [2] ethereum.org. “JSON-RPC API.” Accessed Sep 26, 2026.
Developers

Chain ID FAQ

What is the chain ID of Ethereum?

Ethereum mainnet uses chain ID 1 (hex 0x1). Its main testnet, Sepolia, uses 11155111.

Why do wallets show the chain ID in hex?

The JSON-RPC API returns numbers in hexadecimal. 8453 in decimal is 0x2105 in hex; both mean Base.

How this page works

Sources: Ethereum Improvement Proposals, ethereum.org. Data as of Sep 26, 2026.

How we review

Not affiliated with any project listed. Educational content, not financial advice.