Recursive Length Prefix Encoding Module

Usage no npm install needed!

<script type="module">
  import rlp from 'https://cdn.skypack.dev/rlp';



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Recursive Length Prefix encoding for Node.js and the browser.


npm install rlp

install with -g if you want to use the CLI.


import assert from 'assert'
import RLP from 'rlp'

const nestedList = [[], [[]], [[], [[]]]]
const encoded = RLP.encode(nestedList)
const decoded = RLP.decode(encoded)
assert.deepEqual(nestedList, decoded)


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.

Buffer compatibility

If you would like to continue using Buffers like in rlp v2, you can use:

import assert from 'assert'
import { arrToBufArr, bufArrToArr } from 'ethereumjs-util'
import RLP from 'rlp'

const bufferList = [Buffer.from('123', 'hex'), Buffer.from('456', 'hex')]
const encoded = RLP.encode(bufArrToArr(bufferList))
const encodedAsBuffer = Buffer.from(encoded)
const decoded = RLP.decode(Uint8Array.from(encodedAsBuffer)) // or RLP.decode(encoded)
const decodedAsBuffers = arrToBufArr(decoded)
assert.deepEqual(bufferList, decodedAsBuffers)


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


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


Tests use mocha.

To run tests and linting: npm test

To auto-fix linting problems run: npm run lint:fix


Install dev dependencies: npm install

Run coverage: npm run coverage

The results will be at: coverage/lcov-report/index.html


See our organizational documentation for an introduction to EthereumJS as well as information on current standards and best practices.

If you want to join for work or do improvements on the libraries have a look at our contribution guidelines.