Introducing the Ethereum chain specification

The Ethereum chain specification is a format used to describe how the Ethereum blockchain should look. It describes what parameters, components, and elements it should have to actually be considered an Ethereum blockchain, so that you can create your own private Ethereum blockchains with different properties for testing your applications or forking a new version of Ethereum. The spec defines what you need to create your own blockchain. For instance, WhaleCoin used the Ethereum specification to create a new blockchain with the same core technology, but with their own modifications, thanks to the Ethereum chain spec.

It is important to have a clear specification that tells us how to create our own Ethereum-like blockchain, because hard forks are an elemental part of every blockchain, and because advanced developers may feel that they want more control for testing their applications on private blockchains. Ethereum gives people the choice to create their own system based on Ethereum; in my opinion, this is really good as a developer or miner that processes transactions because, for instance, you can change the consensus algorithm, the gas costs per transaction, the block times, and so on, while still having a valid Ethereum blockchain.

With the Ethereum chain spec, you can create forks or your own private Ethereum blockchain as a testing tool to see how your smart contract code would interact in the real world.