An EVM chain ID identifies the execution chain a signed transaction targets. For a bridge transfer, each onchain leg is signed for its own network: Ethereum mainnet uses chain ID 1, while Polygon PoS uses 137. The ID helps prevent a signed transaction from being replayed unchanged on another chain, but it does not specify the bridge route or destination asset.
What does a chain ID identify?
A chain ID is a number configured by an EVM chain and used in replay-protected transaction signing. Wallets can query an RPC endpoint with eth_chainId; the result is a hexadecimal quantity, so Ethereum mainnet returns 0x1 and Polygon PoS returns 0x89 (decimal 137). EIP-695 defines that RPC method, and EIP-155 describes how the ID protects signed transactions.
Common values for this route include:
- 1: Ethereum mainnet.
- 137: Polygon PoS mainnet.
- 11155111: Ethereum’s Sepolia testnet.
- 80002: Polygon PoS’s Amoy testnet.
Testnet IDs are useful for recognizing test transactions, but they do not make test assets usable on mainnet. A wallet connected to chain ID 80002 is signing for Amoy, even if the asset symbol or address looks familiar. Check the intended network before approving a transaction.
How does the ID enter a signed transaction?
With EIP-155 replay protection, the chain ID is part of the transaction’s signing data. For a modern type-2 EIP-1559 transaction, the payload includes chain_id alongside the nonce, fee fields, gas limit, recipient, value, calldata and access list; the signature authenticates that payload. A node checks that the signed transaction’s ID matches its own configured chain ID before accepting it.
That is why the same wallet address can make separate transactions on Ethereum and Polygon PoS without sharing a single nonce sequence. Each chain keeps its own account state and nonce. If a wallet prepares a Polygon transaction while the signer is on Ethereum, it should reject the mismatch or ask to switch networks; if it does not, stop and check the network and transaction details.
A chain ID is not an RPC address or proof that an endpoint is trustworthy. An endpoint can report a familiar ID while serving stale, faulty or misleading data, and separate chains can be configured with the same number. For an occasional transfer, confirm the wallet’s network label and compare the ID with a trusted network reference; for higher assurance, verify the endpoint and chain state through independent sources.
What role does chain ID play in a bridge transfer?
It identifies the network for each transaction, while the bridge’s contracts and message verification govern how the asset moves between them. In a Polygon PoS deposit, for example, the user signs a transaction on Ethereum to start the deposit; the bridge’s contracts apply the token-specific rules, and the corresponding asset becomes available on Polygon after the required cross-chain processing. A withdrawal starts on Polygon PoS and requires its own steps before the asset can be released on Ethereum.
Predicate contracts enforce asset-specific deposit and exit behavior, while bridge message and proof mechanisms establish that the cross-chain action is valid. The chain ID does not prove that a deposit occurred, authenticate a token mapping, or tell the destination chain which contract action to perform. Those details belong to the bridge protocol. Polygon Portal documents the Polygon PoS bridge, and Polygon Bridge is a way to move supported tokens between Ethereum and Polygon.
For a real example, suppose you hold a supported token on Ethereum and want its Polygon representation. The deposit transaction must be signed on chain ID 1 and submitted to the Ethereum-side bridge contracts. After the bridge’s required processing, the corresponding destination action takes place on chain ID 137. The wallet may need to be on Polygon for a later transaction there, such as spending the received tokens; that is a separate transaction with its own nonce and gas.
What should you verify before signing?
Check the network for the transaction you are about to sign, not merely the network where the token appears in your wallet. For Ethereum-to-Polygon bridging, expect the deposit leg to use Ethereum mainnet’s ID 1; a later Polygon transaction should use 137. To understand the route choice and transfer sequence in more detail, read how to choose a Polygon Bridge route.
Also inspect the transaction’s destination and calldata summary when your wallet provides one. A valid chain ID only means the transaction is bound to that configured chain; it does not mean the recipient contract or requested action is the one you intended. If the wallet’s network and the transaction summary disagree with the route you chose, reject the signature and recheck the bridge context.
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