Contributing

Thanks for your interest in contributing to Viem! Please take a moment to review this document before submitting a pull request.

If you want to contribute, but aren't sure where to start, you can create a new discussion.

If you are contributing to add a new chain to viem/chains, please read the Chains section.

Rules

Significant changes to the API or implementation must be reviewed before a Pull Request is created. Create a Feature Request first to discuss any API changes or new ideas.
Contributors must be humans, not bots.
Contributor GitHub Accounts must have at least one non-trivial contribution to another repository.
First time contributions must not contain only spelling or grammatical fixes.

Basic guide

This guide is intended to help you get started with contributing. By following these steps, you will understand the development process and workflow.

Cloning the repository
Installing Node.js and pnpm
Installing Foundry
Installing dependencies
Running the test suite
Writing documentation
Submitting a pull request
Versioning

Cloning the repository

To start contributing to the project, clone it to your local machine using git:

git clone https://github.com/wevm/viem.git --recurse-submodules

Or the GitHub CLI:

gh repo clone wevm/viem -- --recurse-submodules

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Installing Node.js and pnpm

Viem uses pnpm workspaces to manage multiple projects. You need to install Node.js v22 or higher and pnpm v9.1.0 or higher.

You can run the following commands in your terminal to check your local Node.js and pnpm versions:

node -v
pnpm -v

If the versions are not correct or you don't have Node.js or pnpm installed, download and follow their setup instructions:

Install Node.js using fnm or from the official website
Install pnpm

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Installing Foundry

Viem uses Foundry for testing. We run a local Anvil instance against a forked Ethereum node, where we can also use tools like Forge to deploy test contracts to it.

Install Foundry using the following command:

curl -L https://foundry.paradigm.xyz | bash

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Installing dependencies

Once in the project's root directory, run the following command to install the project's dependencies:

pnpm install

After the install completes, pnpm links packages across the project for development and git hooks are set up.

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Running the test suite

First, add the following to your environment (recommended to use direnv):

VITE_ANVIL_FORK_URL=
VITE_ANVIL_FORK_URL_OPTIMISM=
VITE_ANVIL_FORK_URL_OPTIMISM_SEPOLIA=
VITE_ANVIL_FORK_URL_SEPOLIA=
VITE_ANVIL_FORK_URL_ZKSYNC=
VITE_BATCH_MULTICALL=false
VITE_NETWORK_TRANSPORT_MODE=http

VITE_ANVIL_FORK_URL can be for any RPC service provider (e.g. Alchemy or Infura) for the mainnet. Now you are ready to run the tests!

pnpm test — runs tests in watch mode

Sometimes there may be some tests which fail unexpectedly – you can press f to rerun them and they should pass.

When adding new features or fixing bugs, it's important to add test cases to cover the new/updated behavior.

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Writing documentation

Documentation is crucial to helping developers of all experience levels use Viem. Viem uses Vocs and Markdown for the documentation site (located at site). To start the site in dev mode, run:

pnpm docs:dev

Try to keep documentation brief and use plain language so folks of all experience levels can understand. If you think something is unclear or could be explained better, you are welcome to open a pull request.

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Submitting a pull request

When you're ready to submit a pull request, you can follow these naming conventions:

Pull request titles use the Imperative Mood (e.g., Add something, Fix something).
Changesets use past tense verbs (e.g., Added something, Fixed something).

When you submit a pull request, GitHub will automatically lint, build, and test your changes. If you see an ❌, it's most likely a bug in your code. Please, inspect the logs through the GitHub UI to find the cause.

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Versioning

When adding new features or fixing bugs, we'll need to bump the package versions. We use Changesets to do this.

Note

Only changes to the codebase that affect the public API or existing behavior (e.g. bugs) need changesets.

Each changeset defines which package(s) should be published and whether the change should be a major/minor/patch release, as well as providing release notes that will be added to the changelog upon release.

To create a new changeset, run pnpm changeset. This will run the Changesets CLI, prompting you for details about the change. You’ll be able to edit the file after it’s created — don’t worry about getting everything perfect up front.

Even though you can technically use any markdown formatting you like, headings should be avoided since each changeset will ultimately be nested within a bullet list. Instead, bold text should be used as section headings.

If your PR is making changes to an area that already has a changeset (e.g. there’s an existing changeset covering theme API changes but you’re making further changes to the same API), you should update the existing changeset in your PR rather than creating a new one.

✅ Now you're ready to contribute to Viem!

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Chains

If you wish to contribute to add an additional Chain to the viem/chains entrypoint, there are a few requirements to note before submitting a pull request.

Requirements

Must haves:
- chain must be merged into ethereum-lists/chains,
- a unique Chain ID (id),
- a human-readable name (name),
- a native currency reference (nativeCurrency),
- a public, credible RPC URL (rpcUrls.default)
Nice to haves
- a block explorer (blockExplorers)
- a multicall3 contract (contracts.multicall3)
  - this contract must be verified, and must match the bytecode of the multicall3 contract.
Optional
- ENS registry contract (contracts.ensRegistry)
- testnet flag (testnet)

If your Chain satisfies the necessary criteria, you may submit a pull request for consideration. If your pull request does not satisfy the criteria, it will be closed.

Attribute reference

The Chain type has a number of important attributes, and you may get stuck on what to add to these. Most of these attributes exist within the ethereum-lists/chains repository.

id: The Chain ID for the network. This can be found by typing the network name into ChainList. Example: "Ethereum Mainnet" has a Chain ID of 1.
name: A human readable name for the network. Example: "Binance Smart Chain Mainnet"
nativeCurrency: The native currently of the network. Found from ethereum-lists/chains.
rpcUrls: A set of RPC URLs for the chain. Found from ethereum-lists/chains.
blockExplorers: A set of block explorers for the chain. Found from ethereum-lists/chains.
contracts: A set of deployed contracts for the Chain.
- multicall3 is optional, but it's address is most likely 0xca11bde05977b3631167028862be2a173976ca11 – you can find the deployed block number on the block explorer. Found from mds1/multicall.
- ensRegistry is optional – not all Chains have an ENS Registry. See ENS Deployments for more info.
- ensUniversalResolver is optional – not all Chains have an ENS Universal Resolver.
testnet: Whether or not the Chain is a testnet.

Adding a chain

1. Read the contributing guide

Read the Basic Guide to contributing to set up your environment.

2. Create a chain file

Create a file for your chain in src/chains/definitions/.

Example:

 src/
 ├─ chains/
 │  ├─ definitions/
 │  │  ├─ avalanche.ts
 │  │  ├─ ...
+│  │  ├─ example.ts
 │  │  ├─ ...
 │  │  ├─ zora.ts
 │  ├─ index.ts

3. Define your chain

Define your chain data in defineChain.

Example:

// src/chains/definitions/example.ts
import { defineChain } from '../../utils/chain/defineChain.js'

export const mainnet = /*#__PURE__*/ defineChain({
  id: 1,
  name: 'Example Chain',
  nativeCurrency: { name: 'Example', symbol: 'ETH', decimals: 18 },
  rpcUrls: {
    default: {
      http: ['https://example.com'],
    },
  },
  blockExplorers: {
    default: {
      name: 'Etherscan',
      url: 'https://etherscan.io',
      apiUrl: 'https://api.etherscan.io/api',
    },
  },
  contracts: {
    multicall3: {
      address: '0xca11bde05977b3631167028862be2a173976ca11',
      blockCreated: 69420,
    },
  },
})

4. Export your chain

Export the chain in src/chains/index.ts.

Example:

export type { Chain } from '../types/chain.js'

export { arbitrum } from './definitions/arbitrum.js'
...
+export { example } from './definitions/example.js'
...
export { zora } from './definitions/zora.js'

5. Add changeset

Add a patch changeset with the description "Added <your chain here> chain.".

> pnpm changeset

What kind of change is this for Viem?
+ patch

Please enter a summary for this change
+ Added Example chain.

6. Open your PR

Now you are ready to open your Pull Request.

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CONTRIBUTING.md

CONTRIBUTING.md

Contributing

Rules

Basic guide

Cloning the repository

Installing Node.js and pnpm

Installing Foundry

Installing dependencies

Running the test suite

Writing documentation

Submitting a pull request

Versioning

Chains

Requirements

Attribute reference

Adding a chain

1. Read the contributing guide

2. Create a chain file

3. Define your chain

4. Export your chain

5. Add changeset

6. Open your PR

Files

CONTRIBUTING.md

Latest commit

History

CONTRIBUTING.md

File metadata and controls

Contributing

Rules

Basic guide

Cloning the repository

Installing Node.js and pnpm

Installing Foundry

Installing dependencies

Running the test suite

Writing documentation

Submitting a pull request

Versioning

Chains

Requirements

Attribute reference

Adding a chain

1. Read the contributing guide

2. Create a chain file

3. Define your chain

4. Export your chain

5. Add changeset

6. Open your PR