@ethereumjs/rlp/README.md

Recursive Length Prefix Encoding Module

# @ethereumjs/rlp `v10`

[![NPM Package][rlp-npm-badge]][rlp-npm-link]
[![GitHub Issues][rlp-issues-badge]][rlp-issues-link]
[![Actions Status][rlp-actions-badge]][rlp-actions-link]
[![Code Coverage][rlp-coverage-badge]][rlp-coverage-link]
[![Discord][discord-badge]][discord-link]

| [Recursive Length Prefix](https://ethereum.org/en/developers/docs/data-structures-and-encoding/rlp) encoding for Node.js and the browser. |
| ----------------------------------------------------------------------------------------------------------------------------------------- |

## Table of Contents

- [Installation](#installation)
- [Usage](#usage)
- [Browser](#browser)
- [API](#api)
- [CLI](#cli)
- [EthereumJS](#ethereumjs)
- [License](#license)

## Installation

To obtain the latest version, simply require the project using `npm`:

```shell
npm install @ethereumjs/rlp
```

Install with `-g` if you want to use the CLI.

## Usage

```ts
// ./examples/simple.ts

import assert from 'assert'
import { RLP } from '@ethereumjs/rlp'

const nestedList = [[], [[]], [[], [[]]]]
const encoded = RLP.encode(nestedList)
const decoded = RLP.decode(encoded)
assert.deepStrictEqual(decoded, nestedList, 'decoded output does not match original')
console.log('assert.deepStrictEqual would have thrown if the decoded output did not match')

```

## Browser

We provide hybrid ESM/CJS builds for all our libraries. With the v10 breaking release round from Spring 2025, all libraries are "pure-JS" by default and we have eliminated all hard-wired WASM code. Additionally we have substantially lowered the bundle sizes, reduced the number of dependencies, and cut out all usages of Node.js-specific primitives (like the Node.js event emitter).

It is easily possible to run a browser build of one of the EthereumJS libraries within a modern browser using the provided ESM build. For a setup example see [./examples/browser.html](./examples/browser.html).

## API

`RLP.encode(plain)` - RLP encodes an `Array`, `Uint8Array` or `String` and returns a `Uint8Array`.

`RLP.decode(encoded, [stream=false])` - Decodes an RLP encoded `Uint8Array`, `Array` or `String` and returns a `Uint8Array` or `NestedUint8Array`. If `stream` is enabled, it will just decode the first rlp sequence in the Uint8Array. By default, it would throw an error if there are more bytes in Uint8Array than used by the rlp sequence.

## CLI

`rlp encode <JSON string>`\
`rlp decode <0x-prefixed hex string>`

### Examples

- `rlp encode '5'` -> `0x05`
- `rlp encode '[5]'` -> `0xc105`
- `rlp encode '["cat", "dog"]'` -> `0xc88363617483646f67`
- `rlp decode 0xc88363617483646f67` -> `["cat","dog"]`

## EthereumJS

The `EthereumJS` GitHub organization and its repositories are managed by members of the former Ethereum Foundation JavaScript team and the broader Ethereum community. If you want to join for work or carry out improvements on the libraries see the [developer docs](../../DEVELOPER.md) for an overview of current standards and tools and review our [code of conduct](../../CODE_OF_CONDUCT.md).

## License

[MPL-2.0](<https://tldrlegal.com/license/mozilla-public-license-2.0-(mpl-2)>)

[discord-badge]: https://img.shields.io/static/v1?logo=discord&label=discord&message=Join&color=blue
[discord-link]: https://discord.gg/TNwARpR
[rlp-npm-badge]: https://img.shields.io/npm/v/@ethereumjs/rlp.svg
[rlp-npm-link]: https://www.npmjs.com/package/@ethereumjs/rlp
[rlp-issues-badge]: https://img.shields.io/github/issues/ethereumjs/ethereumjs-monorepo/package:%20rlp?label=issues
[rlp-issues-link]: https://github.com/ethereumjs/ethereumjs-monorepo/issues?q=is%3Aopen+is%3Aissue+label%3A"package%3A+rlp"
[rlp-actions-badge]: https://github.com/ethereumjs/ethereumjs-monorepo/actions/workflows/static-build.yml/badge.svg
[rlp-actions-link]: https://github.com/ethereumjs/ethereumjs-monorepo/actions?query=workflow%3A%22rlp%22
[rlp-coverage-badge]: https://codecov.io/gh/ethereumjs/ethereumjs-monorepo/branch/master/graph/badge.svg?flag=rlp
[rlp-coverage-link]: https://codecov.io/gh/ethereumjs/ethereumjs-monorepo/tree/master/packages/rlp