Chain Forking

Overview

Chain forking creates a local copy of a live blockchain network. Your local environment gets the complete state of the target network — all contracts, all balances, all storage — at a specific block. This lets you:

Test against real DeFi protocols — Interact with Uniswap, Aave, Compound, etc. locally
Reproduce mainnet bugs — Fork at the block before a bug and replay the transaction
Test token integrations — Use real USDC, WETH, DAI balances in your tests
Simulate governance — Impersonate any address and execute transactions

Quick Start

# Start your environment
dokrypt up

# Fork Ethereum mainnet at the latest block
dokrypt fork mainnet

# Fork at a specific block
dokrypt fork mainnet --block 18500000

# Fork Polygon
dokrypt fork polygon

Supported Networks

Network	Aliases	Chain ID	Public RPC
Ethereum	`mainnet`, `ethereum`	1	`https://eth.llamarpc.com`
Sepolia	`sepolia`	11155111	`https://rpc.sepolia.org`
Goerli	`goerli`	5	`https://rpc.ankr.com/eth_goerli`
Polygon	`polygon`	137	`https://polygon-rpc.com`
Arbitrum	`arbitrum`	42161	`https://arb1.arbitrum.io/rpc`
Optimism	`optimism`	10	`https://mainnet.optimism.io`
Base	`base`	8453	`https://mainnet.base.org`
BSC	`bsc`	56	`https://bsc-dataseed.binance.org`
Avalanche	`avalanche`	43114	`https://api.avax.network/ext/bc/C/rpc`

Using Custom RPC URLs

For faster forks or private access, use your own RPC URL:

dokrypt fork --url https://eth-mainnet.alchemyapi.io/v2/YOUR_KEY

Or with the --fork flag on dokrypt up:

dokrypt up --fork mainnet
dokrypt up --fork polygon --fork-block 50000000

Fork on Startup via Config

You can configure forking directly in dokrypt.yaml:

chains:
  ethereum:
    engine: anvil
    chain_id: 31337
    fork:
      network: mainnet
      block_number: 18500000

Use Cases

Test Against Uniswap

# Fork mainnet
dokrypt fork mainnet

# Your local chain now has all of Uniswap's contracts
# Interact with the Router at 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D

Impersonate a Whale

# Fork mainnet
dokrypt fork mainnet

# Impersonate a USDC whale
dokrypt accounts impersonate 0x47ac0Fb4F2D84898e4D9E7b4DaB3C24507a6D503

# Now you can send USDC from this address without the private key

Reproduce a Bug

# Fork at the block just before the bug
dokrypt fork mainnet --block 17999999

# Impersonate the affected account
dokrypt accounts impersonate 0xAffectedAddress...

# Replay or investigate

Multi-chain Fork

If your dokrypt.yaml has multiple chains, specify which one to fork:

dokrypt fork mainnet --chain l1
dokrypt fork polygon --chain l2

How It Works

Resolution — The network name is resolved to an RPC URL
Reset — anvil_reset (or hardhat_reset) is called with the fork configuration
Wait — Dokrypt waits up to 120 seconds for the fork to complete
Funding — Test accounts are funded with 10,000 ETH each
Ready — The local chain is now a fork of the target network

Forking from public RPCs can be slow. For production testing, use a dedicated RPC provider (Alchemy, Infura, QuickNode) for much faster fork times.

Getting Started

Core Concepts

Features

Advanced

Overview

Quick Start

Supported Networks

Using Custom RPC URLs

Fork on Startup via Config

Use Cases

Test Against Uniswap

Impersonate a Whale

Reproduce a Bug

Multi-chain Fork

How It Works

​Overview

​Quick Start

​Supported Networks

​Using Custom RPC URLs

​Fork on Startup via Config

​Use Cases

​Test Against Uniswap

​Impersonate a Whale

​Reproduce a Bug

​Multi-chain Fork

​How It Works

Overview

Quick Start

Supported Networks

Using Custom RPC URLs

Fork on Startup via Config

Use Cases

Test Against Uniswap

Impersonate a Whale

Reproduce a Bug

Multi-chain Fork

How It Works