CAIP-3: Blockchain Reference for the EIP155 Namespace

Author Simon Warta, ligi, Pedro Gomes
Status Superseded
Type Standard
Created 2019-12-05
Updated 2020-01-16
Requires 2
Superseded By

Simple Summary

This document is about the details of the EIP155 namespace and reference for CAIP-2.


In CAIP-2 a general blockchain identification scheme is defined. This is the implementation of CAIP-2 for EIP155 (Ethereum).


See CAIP-2.


EIP155 Namespace

The namespace is called “eip155” as in EIP155.

Reference Definition

The definition is delegated to EIP155. The format is an unsigned integer in decimal representation and corresponds to CHAIN_ID of EIP155.

Note: due to length restrictions of the reference field (32 characters), the largest supported CHAIN_ID is 99999999999999999999999999999999.

Resolution Method

To resolve a blockchain reference for the EIP155 namespace, make a JSON-RPC request to the blockchain node with method eth_chainId, for example:

// Request
  "id": 1,
  "jsonrpc": "2.0",
  "method": "eth_chainId",
  "params": []

// Response
  "id": 1,
  "jsonrpc": "2.0",
  "result": "0x1"

The response will return as a value for the result a base 16 encoded integer that should be converted to base 10 to format a CAIP-3 compatible blockchain reference.


The chain ID defined in EIP155 is the most widely used chain identifier in the Ethereum ecosystem known to the authors. It strives for uniqueness and the fact that the standard is used for replay protection ensure that creators of a new Ethereum network have an incentive to use an ID that is not used elsewhere.

Backwards Compatibility

Not applicable

Test Cases

This is a list of manually composed examples

# Ethereum mainnet

# Görli

# Auxilium Network Mainnet

Copyright and related rights waived via CC0.


Please cite this document as:

Simon Warta, ligi, Pedro Gomes, "CAIP-3: Blockchain Reference for the EIP155 Namespace," Chain Agnostic Improvement Proposals, no. 3, December 2019. [Online serial]. Available: