> ## Documentation Index
> Fetch the complete documentation index at: https://docs.dokrypt.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Chains

> Configure blockchain nodes — engines, forking, mining, and accounts.

## Overview

Each entry under `chains:` in `dokrypt.yaml` defines a local blockchain node. You can run multiple chains simultaneously for multi-chain development.

## Basic Configuration

```yaml theme={null}
chains:
  ethereum:
    engine: anvil
    chain_id: 31337
```

## Engines

Dokrypt supports three EVM node engines:

| Engine    | Description     | Best For                         |
| --------- | --------------- | -------------------------------- |
| `anvil`   | Foundry's Anvil | Default. Fastest, most features. |
| `hardhat` | Hardhat Network | Hardhat ecosystem compatibility  |
| `geth`    | Go-Ethereum     | Closest to production            |

```yaml theme={null}
chains:
  ethereum:
    engine: anvil     # or hardhat, geth
```

## Chain ID

```yaml theme={null}
chains:
  ethereum:
    chain_id: 31337   # Any integer
```

Common local chain IDs: `31337` (Hardhat/Anvil default), `1337` (Geth default).

## Block Time

Controls how frequently blocks are produced.

```yaml theme={null}
chains:
  ethereum:
    block_time: "2s"  # Produce a block every 2 seconds
```

| Value             | Behavior                                   |
| ----------------- | ------------------------------------------ |
| `"0s"` or omitted | Instant mining (mine on every transaction) |
| `"1s"` - `"12s"`  | Timed block production                     |
| `"12s"`           | Simulates Ethereum mainnet                 |

## Mining Modes

```yaml theme={null}
chains:
  ethereum:
    mining:
      mode: auto       # auto | interval | manual
      interval: "2s"   # Only for interval mode
```

| Mode       | Behavior                                                     |
| ---------- | ------------------------------------------------------------ |
| `auto`     | Mine a block on every transaction                            |
| `interval` | Mine at fixed intervals                                      |
| `manual`   | Only mine when explicitly requested via `dokrypt chain mine` |

## Accounts

```yaml theme={null}
chains:
  ethereum:
    accounts: 10                        # Number of test accounts
    account_balance: "10000"            # Balance in ETH
    # OR
    balance: "10000000000000000000000"  # Balance in wei
```

## EVM Configuration

```yaml theme={null}
chains:
  ethereum:
    gas_limit: 30000000       # Block gas limit
    base_fee: 1000000000      # Base fee in wei (1 gwei)
    hardfork: shanghai        # london | shanghai | cancun
    code_size_limit: 24576    # Max contract code size
    auto_impersonate: false   # Auto-impersonate all accounts
```

## Forking

Fork a live network on startup:

```yaml theme={null}
chains:
  ethereum:
    fork:
      network: mainnet          # Network name
      block_number: 18500000    # Fork at specific block (0 = latest)
```

With a custom RPC URL:

```yaml theme={null}
chains:
  ethereum:
    fork:
      rpc_url: "${ALCHEMY_URL}"
      block_number: 18500000
```

Supported network names: `mainnet`, `ethereum`, `sepolia`, `goerli`, `polygon`, `arbitrum`, `optimism`, `base`, `bsc`, `avalanche`.

## Genesis Accounts

Pre-fund specific addresses at genesis:

```yaml theme={null}
chains:
  ethereum:
    genesis_accounts:
      - address: "0x1234567890abcdef1234567890abcdef12345678"
        balance: "1000000000000000000000"  # 1000 ETH in wei
      - address: "0xabcdef1234567890abcdef1234567890abcdef12"
        balance: "500000000000000000000"   # 500 ETH in wei
```

## Auto-Deploy

Deploy contracts automatically when the chain starts:

```yaml theme={null}
chains:
  ethereum:
    deploy:
      - artifact: "contracts/MyToken.sol:MyToken"
        constructor_args: ["MyToken", "MTK", 1000000]
        label: "token"
      - artifact: "contracts/Registry.sol:Registry"
        label: "registry"
```

## Multi-Chain Setup

Run multiple chains for cross-chain development:

```yaml theme={null}
chains:
  ethereum:
    engine: anvil
    chain_id: 31337
    block_time: "2s"
  polygon:
    engine: anvil
    chain_id: 137
    block_time: "2s"
  arbitrum:
    engine: anvil
    chain_id: 42161
    block_time: "1s"
```

Use `--chain` flag to target a specific chain:

```bash theme={null}
dokrypt chain info --chain polygon
dokrypt chain mine 10 --chain arbitrum
dokrypt fork mainnet --chain ethereum
```

## Default Ports

Each chain gets a unique RPC port (assigned dynamically). The first chain typically gets port 8545.

| Chain (in order) | Default RPC Port |
| ---------------- | ---------------- |
| First chain      | 8545             |
| Second chain     | 8546             |
| Third chain      | 8547             |