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A module to store and interact with blocks.

Note: this README reflects the state of the library from v5.0.0 onwards. See README from the standalone repository for an introduction on the last preceding release.


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

npm install @ethereumjs/blockchain

Note: If you want to work with EIP-4844 related functionality, you will have additional manual installation steps for the KZG setup, see related section below.



The Blockchain package represents an Ethereum-compatible blockchain storing a sequential chain of @ethereumjs/block blocks and holding information about the current canonical head block as well as the context the chain is operating in (e.g. the hardfork rules the current head block adheres to).

New blocks can be added to the blockchain. Validation ensures that the block format adheres to the given chain rules (with the Blockchain.validateBlock() function) and consensus rules (Blockchain.consensus.validateConsensus()).

The library also supports reorg scenarios e.g. by allowing to add a new block with Blockchain.putBlock() which follows a different canonical path to the head than given by the current canonical head block.


The following is an example to instantiate a simple Blockchain object, put blocks into the blockchain and then iterate through the blocks added:

// ./examples/simple.ts

import { Block } from '@ethereumjs/block'
import { Blockchain } from '@ethereumjs/blockchain'
import { Common, Hardfork } from '@ethereumjs/common'
import { bytesToHex } from '@ethereumjs/util'

const main = async () => {
  const common = new Common({ chain: 'mainnet', hardfork: Hardfork.London })
  // Use the safe static constructor which awaits the init method
  const blockchain = await Blockchain.create({
    validateBlocks: false, // Skipping validation so we can make a simple chain without having to provide complete blocks
    validateConsensus: false,

  // We use minimal data to provide a sequence of blocks (increasing number, difficulty, and then setting parent hash to previous block)
  const block = Block.fromBlockData(
      header: {
        number: 1n,
        parentHash: blockchain.genesisBlock.hash(),
        difficulty: blockchain.genesisBlock.header.difficulty + 1n,
    { common, setHardfork: true }
  const block2 = Block.fromBlockData(
      header: {
        number: 2n,
        parentHash: block.header.hash(),
        difficulty: block.header.difficulty + 1n,
    { common, setHardfork: true }
  // See @ethereumjs/block for more details on how to create a block
  await blockchain.putBlock(block)
  await blockchain.putBlock(block2)

  // We iterate over the blocks in the chain to the current head (block 2)
  await blockchain.iterator('i', (block) => {
    const blockNumber = block.header.number.toString()
    const blockHash = bytesToHex(block.hash())
    console.log(`Block ${blockNumber}: ${blockHash}`)

  // Block 1: 0xa1a061528d74ba81f560e1ebc4f29d6b58171fc13b72b876cdffe6e43b01bdc5
  // Block 2: 0x5583be91cf9fb14f5dbeb03ad56e8cef19d1728f267c35a25ba5a355a528f602

Database Abstraction / Removed LevelDB Dependency

With the v7 release the Blockchain library database has gotten an additional abstraction layer which allows to switch the backend to whatever is fitting the best for a use case, see PR #2669 and PR #2673. The database just needs to conform to the new DB interface provided in the @ethereumjs/util package (since this is used in other places as well).

By default the blockchain package now uses a MapDB non-persistent data storage which is also generically provided in the @ethereumjs/util package.

If you need a persistent data store for your use case you can consider using the wrapper we have written within our client library.


Starting with v6 there is a dedicated consensus class for each type of supported consensus, Ethash, Clique and Casper (PoS, this one is rather the do-nothing part of Casper and letting the respective consensus/beacon client do the hard work! 🙂). Each consensus class adheres to a common interface Consensus implementing the following five methods in a consensus-specific way:

  • genesisInit(genesisBlock: Block): Promise<void>
  • setup(): Promise<void>
  • validateConsensus(block: Block): Promise<void>
  • validateDifficulty(header: BlockHeader): Promise<void>
  • newBlock(block: Block, commonAncestor?: BlockHeader, ancientHeaders?: BlockHeader[]): Promise<void>

Custom Consensus Algorithms

Also part of V6, you can also create a custom consensus class implementing the above interface and pass it into the Blockchain constructor using the consensus option at instantiation. See this test script for a complete example of how write and use a custom consensus implementation.

Note, if you construct a blockchain with a custom consensus implementation, transition checks for switching from PoW to PoS are disabled so defining a merge hardfork will have no impact on the consensus mechanism defined for the chain.

Custom Genesis State

Genesis in v7 (removed genesis dependency)

Genesis state was huge and had previously been bundled with the Blockchain package with the burden going over to the VM, since Blockchain is a dependency.

Starting with the v7 release genesis state has been removed from blockchain and moved into its own auxiliary package @ethereumjs/genesis, from which it can be included if needed (for most - especially VM - use cases it is not necessary), see PR #2844.

This goes along with some changes in Blockchain and VM API:

  • Blockchain: There is a new constructor option genesisStateRoot beside genesisBlock and genesisState for an alternative condensed way to provide the genesis state root directly
  • Blockchain: genesisState(): GenesisState method has been replaced by the async getGenesisStateRoot(chainId: Chain): Promise<Uint8Array> method
  • VM: activateGenesisState?: boolean constructor option has been replaced with a genesisState?: GenesisState option

Genesis in v6

For the v6 release responsibility for setting up a custom genesis state moved from the Common library to the Blockchain package, see PR #1924 for some work context.

A genesis state can be set along Blockchain creation by passing in a custom genesisBlock and genesisState. For mainnet and the official test networks like sepolia or goerli genesis is already provided with the block data coming from @ethereumjs/common. The genesis state is being integrated in the Blockchain library (see genesisStates folder).

Custom genesis from a Geth genesis config

For many custom chains we might come across a genesis configuration, which can be used to build both chain config as well the genesis state (and hence the genesis block as well to start off with)

// ./examples/gethGenesis.ts

import { Blockchain } from '@ethereumjs/blockchain'
import { Common, parseGethGenesis } from '@ethereumjs/common'
import { bytesToHex, parseGethGenesisState } from '@ethereumjs/util'
import gethGenesisJson from './genesisData/post-merge.json'

const main = async () => {
  // Load geth genesis json file into lets say `gethGenesisJson`
  const common = Common.fromGethGenesis(gethGenesisJson, { chain: 'customChain' })
  const genesisState = parseGethGenesisState(gethGenesisJson)
  const blockchain = await Blockchain.create({
  const genesisBlockHash = blockchain.genesisBlock.hash()
    `Genesis hash from geth genesis parameters - ${bytesToHex(blockchain.genesisBlock.hash())}`


The genesis block from the initialized Blockchain can be retrieved via the Blockchain.genesisBlock getter. For creating a genesis block from the params in @ethereumjs/common, the createGenesisBlock(stateRoot: Buffer): Block method can be used.

Supported Blocks and Tx Types

EIP-1559 Support

This library supports the handling of EIP-1559 blocks and transactions starting with the v5.3.0 release.

EIP-4844 Shard Blob Transactions Support

This library supports the blob transaction type introduced with EIP-4844 as being specified in the b9a5a11 EIP version from July 2023 deployed along 4844-devnet-7 (July 2023), see PR #2349 and following.

Note: 4844 support is not yet completely stable and there will still be (4844-)breaking changes along all types of library releases.

The blockchain library now allows for blob transactions to be validated and included in a chain where EIP-4844 activated either by hardfork or standalone EIP (see latest tx library release for additional details).


With the breaking release round in Summer 2023 we have added hybrid ESM/CJS builds for all our libraries (see section below) and have eliminated many of the caveats which had previously prevented a frictionless browser usage.

It is now 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.



Generated TypeDoc API Documentation

Hybrid CJS/ESM Builds

With the breaking releases from Summer 2023 we have started to ship our libraries with both CommonJS (cjs folder) and ESM builds (esm folder), see package.json for the detailed setup.

If you use an ES6-style import in your code files from the ESM build will be used:

import { EthereumJSClass } from '@ethereumjs/[PACKAGE_NAME]'

If you use Node.js specific require, the CJS build will be used:

const { EthereumJSClass } = require('@ethereumjs/[PACKAGE_NAME]')

Using ESM will give you additional advantages over CJS beyond browser usage like static code analysis / Tree Shaking which CJS can not provide.

Buffer -> Uint8Array

With the breaking releases from Summer 2023 we have removed all Node.js specific Buffer usages from our libraries and replace these with Uint8Array representations, which are available both in Node.js and the browser (Buffer is a subclass of Uint8Array).

We have converted existing Buffer conversion methods to Uint8Array conversion methods in the @ethereumjs/util bytes module, see the respective README section for guidance.

BigInt Support

Starting with v6 the usage of BN.js for big numbers has been removed from the library and replaced with the usage of the native JS BigInt data type (introduced in ES2020).

Please note that number-related API signatures have changed along with this version update and the minimal build target has been updated to ES2020.


For debugging blockchain control flows the debug library is used and can be activated on the CL with DEBUG=[Logger Selection] node [Your Script to Run].js.

The following initial logger is currently available:

Logger Description
blockchain:clique Clique operations like updating the vote and/or signer list

The following is an example for a logger run:

Run with the clique logger:

DEBUG=ethjs,blockchain:clique tsx test.ts


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 carry out improvements on the libraries, please review our contribution guidelines first.





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