Foundry

foundry

Purpose

Foundry is a command-line toolkit for efficiently developing, testing, and deploying Ethereum smart contracts written in Solidity. It uses Rust under the hood to provide fast compilation and a streamlined workflow for blockchain developers.

When to Use

Use Foundry when building or maintaining Solidity-based smart contracts for Ethereum, especially if you need rapid iteration, local testing, or deployment to testnets/mainnets. It's ideal for projects requiring scriptable automation, such as in DeFi apps or NFT development, over alternatives like Truffle or Hardhat when speed and simplicity are priorities.

Key Capabilities

• Compile Solidity contracts with incremental builds for faster development.
• Run unit tests with fuzzing and invariant testing to catch edge cases.
• Deploy contracts to Ethereum networks using customizable scripts.
• Manage dependencies via Git submodules or npm-like remotes.
• Generate ABI and bytecode outputs for integration with dApps.
• Support for EVM-compatible chains beyond Ethereum, like Polygon.

Usage Patterns

Start by initializing a project with forge init, then write contracts in the src directory. Build and test iteratively using forge build and forge test. For deployment, create a script in script and run it with forge script. Always configure networks in foundry.toml for different environments. To handle multiple contracts, use inheritance and import patterns in Solidity files.

Common Commands/API

Foundry operates via CLI commands; no direct API endpoints. Use these in your terminal:

• forge init --no-git: Initialize a new project without creating a Git repo. Example: forge init mycontract.
• forge build --force: Compile all contracts, forcing a rebuild. Snippet:

  cd myproject
  forge build --force

• forge test --fork-url $ETH_RPC_URL: Run tests with a forked mainnet. Use env var for RPC: export ETH_RPC_URL=https://mainnet.infura.io/v3/$INFURA_KEY. Snippet:

  forge test --fork-url $ETH_RPC_URL --fork-block-number 15000000

• forge deploy --rpc-url $ETH_RPC_URL --private-key $ETH_PRIVATE_KEY: Deploy a contract. For auth, set $ETH_PRIVATE_KEY as your wallet key. Snippet:

  forge deploy --rpc-url $ETH_RPC_URL --private-key $ETH_PRIVATE_KEY --broadcast

• forge script script/MyScript.sol:run --sig "run()" --rpc-url $ETH_RPC_URL: Execute a custom script. Config format in foundry.toml: [rpc_endpoints] mainnet = "${ETH_RPC_URL}".

Integration Notes

Integrate Foundry with VS Code by installing the Solidity extension and adding a tasks.json for commands like "forge build". For CI/CD, use GitHub Actions with a step: run: forge test --fork-url ${{ env.ETH_RPC_URL }}. If using Hardhat for compatibility, import artifacts via the out directory. Set env vars for keys: export ETH_PRIVATE_KEY=$YOUR_KEY. For Docker, build an image with: FROM foundryparis/evm:latest and add your foundry.toml for config overrides.

Error Handling

Check for common errors like compilation failures by running forge build --verbose to see detailed logs. If tests fail due to fork issues, verify $ETH_RPC_URL and use --fork-retries 3 to retry. For deployment errors (e.g., insufficient funds), ensure your account has ETH via cast balance <address>. Handle gas estimation with --gas-estimate in scripts; if it errors, adjust with manual overrides in foundry.toml like [etherscan] api_key = "$ETHERSCAN_API_KEY". Always wrap scripts in try-catch for Solidity reverts.

Concrete Usage Examples

1. Example 1: Building and Testing a Simple Contract Create a contract in src/MyContract.sol: contract MyContract { uint public x = 1; }. Then, build it: forge build. Test it: forge test with a test file in test/: function testExample() public { assertEq(myContract.x(), 1); }. This verifies basic functionality in under 5 minutes.

2. Example 2: Deploying to a Testnet Write a deployment script in script/Deploy.sol: function run() public { vm.broadcast(); new MyContract(); }. Run: forge script script/Deploy.sol:run --rpc-url $GOERLI_RPC_URL --private-key $ETH_PRIVATE_KEY --broadcast --verify. This deploys and verifies on Goerli, using Etherscan if configured.

Graph Relationships

• Related to cluster: blockchain
• Connected to tags: ethereum, solidity, smart-contracts
• Depends on: rust, solidity compiler
• Used with: ethers.js for frontend, hardhat for migration compatibility