Local Chain Genesis Block Configurator

WHAT IT DOES

The Local Chain Genesis Block Configurator is a developer tool that generates custom genesis.json configuration files for local EVM chains. It creates the foundational block configuration needed to initialize a new blockchain node, with user-defined chain ID, chain name, initial token allocations, gas limits, and precompile selections. This helps developers quickly spin up local testnets, private chains, or custom EVM environments for smart contract testing, protocol development, and infrastructure experimentation without manual JSON construction.

HOW TO USE

Enter your desired chain name and chain ID (default 1337 for local development). Specify initial allocations by entering addresses and ETH balances in the format "0xaddress:balance" (one per line). Set the gas limit and select which precompiles to enable from the list. Choose your target client (Geth, Erigon, Besu, Nethermind, or Reth) for compatibility. Click "generate genesis.json" to produce the configuration file. The tool displays the complete JSON with a download button and step-by-step instructions for initializing your node with Geth or other clients.

TECHNICAL MECHANISM

The tool constructs a complete Ethereum genesis configuration as a JSON object following the standard format used by Geth and other EVM clients. The config section includes chainId and all required hard fork activation blocks (set to 0 for immediate activation). Allocations are parsed from user input using ethers.parseEther to convert ETH balances to wei, then formatted as hex strings. The alloc object maps each address to its balance in wei. The tool includes precompile options by enabling the corresponding EIPs in the configuration (EIP-152, EIP-2565, EIP-1108, EIP-1962, EIP-198) when selected. The gas limit is user-configurable with a default of 30,000,000. The generated JSON is formatted with proper indentation for readability and includes all standard genesis fields: nonce, timestamp, extraData, difficulty, mixHash, coinbase, number, gasUsed, and parentHash. The tool validates address formats and balance inputs, providing warnings for invalid entries.

WHAT IT CANNOT SEE

The tool cannot actually deploy or initialize local chains—it only generates configuration files. It cannot validate that the generated genesis configuration will work with specific client implementations beyond basic format compatibility. The tool cannot detect invalid addresses or allocation formats without parsing and may silently skip malformed entries. It cannot test that the genesis state is valid without running a node. The tool cannot account for client-specific genesis fields or extensions that may be required by certain clients. It cannot verify that allocated balances are sufficient for intended operations. The tool cannot detect conflicts in precompile addresses or system contract allocations.

PLEASE NOTE

This tool is designed for Ethereum Virtual Machine (EVM) compatible chains only. The generated genesis.json follows the Geth format but may require adjustments for other clients (Erigon, Besu, Nethermind, Reth). Always review the generated file before using it with your node. The tool does not configure consensus engine parameters beyond the standard PoW fields—for PoS chains, additional configuration is needed. Initial allocations are for testing purposes only—do not use real private keys or sensitive addresses. The tool provides a foundation for local chain setup; users should consult their client's documentation for client-specific genesis requirements.