Chain ID

A chain ID is a unique identifier that represents a blockchain network. We use it to distinguish different blockchain networks from each other and to ensure that transactions and messages are sent to the correct network. Your Cosmos EVM blockchain should follow the format of format.

You can also look up the EIP-155 Chain ID by referring to chainlist.org.

The Chain Identifier​

Every chain must have a unique identifier or chain-id. CometBFT requires each application to define its own chain-id in the genesis.json fields. However, to comply with both EIP-155 and Cosmos standard for chain upgrades, Cosmos EVM-compatible chains must implement a special structure for their chain identifiers.

Structure​

A Cosmos EVM Chain ID contains 3 main components

• Identifier: Unstructured string that defines the name of the application.
• EIP-155 Number: Immutable EIP-155 CHAIN_ID that defines the replay attack protection number.
• Version Number: Is the version number (always positive) that the chain is currently running. This number MUST be incremented every time the chain is upgraded or forked to avoid network or consensus errors.

Format​

The format for specifying a Cosmos EVM-compatible chain-id in genesis is the following:

{identifier}_{EIP155}-{version}

The following table provides an example where the second row corresponds to an upgrade from the first one:

ChainID	Identifier	EIP-155 Number	Version Number
cosmoshub-1	cosmoshub	9000	1
cosmoshub-2	cosmoshub	9000	2
...	…	…	…
cosmoshub-N	cosmoshub	9000	N