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# Chain

## Overview

The **Chain** module describes an EVM chain: its id, name, native currency, RPC endpoints, block
explorers, contracts, and optional behavior.

A `Chain` is plain data that can also define:

* **`codecs`**: bidirectional RPC to native codecs.
* **`fees`**: chain-specific fee derivation.
* **`transaction`**: transaction signing and preparation hooks.
* **`verifyHash`**: chain-specific hash verification.

```ts twoslash
import { Chain } from 'viem'

const mainnet = Chain.from({
  id: 1,
  name: 'Ethereum',
  nativeCurrency: { name: 'Ether', symbol: 'ETH', decimals: 18 },
  rpcUrls: { http: 'https://eth.merkle.io' },
})
```

<Cards>
  <Card title="Defining a Chain" description="Define a chain with Chain.from, preserving its literal type." icon="lucide:hammer" to="/docs/chains/create" />

  <Card title="Extending Chains" description="Derive a new chain from a base with the chainable .extend()." icon="lucide:git-branch" to="/docs/chains/extend" />

  <Card title="Customizing Fees" description="Override how fees are derived with the chain's fees config." icon="lucide:fuel" to="/docs/chains/fees" />
</Cards>