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name: rr-solidity description: Comprehensive Solidity smart contract development skill using Foundry framework. Use for writing, testing, deploying, and auditing Solidity contracts with security-first practices. Also triggers when working with .sol files, Foundry project files (foundry.toml), test files (.t.sol), or smart contract deployment scripts. Example triggers: "Write smart contract", "Create Solidity test", "Deploy contract", "Audit smart contract", "Fix security vulnerability", "Write Foundry test", "Set up Foundry project"

Solidity Development with Foundry

Overview

Comprehensive skill for professional Solidity smart contract development using the Foundry framework. Provides security-first development practices, testing patterns, static analysis integration (Slither, solhint), and deployment workflows for EVM-compatible blockchains.

When to Use This Skill

Automatically activate when:

• Working with .sol (Solidity) files
• User mentions smart contracts, blockchain, Web3, DeFi, or Ethereum
• Foundry project detected (foundry.toml present)
• User requests contract deployment, testing, or security auditing
• Working with forge, cast, or anvil commands
• Implementing ERC standards (ERC20, ERC721, ERC1155, etc.)

Development Workflow

1. Write Secure Contracts

Follow security-first patterns from references/solidity-security.md:

Always implement:

• Checks-Effects-Interactions (CEI) pattern
• Access control (Ownable, AccessControl)
• Input validation
• Emergency pause mechanisms
• Pull over push for payments
• Custom errors for gas efficiency

Example contract structure:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.30;

import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
import {Pausable} from "@openzeppelin/contracts/security/Pausable.sol";

contract MyContract is Ownable, Pausable {
    /*//////////////////////////////////////////////////////////////
                                 ERRORS
    //////////////////////////////////////////////////////////////*/

    error InvalidInput();
    error InsufficientBalance();

    /*//////////////////////////////////////////////////////////////
                                 EVENTS
    //////////////////////////////////////////////////////////////*/

    event ActionCompleted(address indexed user, uint256 amount);

    /*//////////////////////////////////////////////////////////////
                            STATE VARIABLES
    //////////////////////////////////////////////////////////////*/

    mapping(address => uint256) public balances;

    /*//////////////////////////////////////////////////////////////
                              CONSTRUCTOR
    //////////////////////////////////////////////////////////////*/

    constructor() Ownable(msg.sender) {}

    /*//////////////////////////////////////////////////////////////
                           EXTERNAL FUNCTIONS
    //////////////////////////////////////////////////////////////*/

    function deposit() external payable whenNotPaused {
        if (msg.value == 0) revert InvalidInput();
        balances[msg.sender] += msg.value;
        emit ActionCompleted(msg.sender, msg.value);
    }

    function withdraw(uint256 amount) external whenNotPaused {
        // CEI Pattern: Checks
        if (amount == 0) revert InvalidInput();
        if (balances[msg.sender] < amount) revert InsufficientBalance();

        // Effects
        balances[msg.sender] -= amount;

        // Interactions
        (bool success, ) = msg.sender.call{value: amount}("");
        require(success, "Transfer failed");

        emit ActionCompleted(msg.sender, amount);
    }
}

2. Write Comprehensive Tests

Follow testing patterns from references/foundry-testing.md:

Test structure:

import {Test, console} from "forge-std/Test.sol";
import {MyContract} from "../src/MyContract.sol";

contract MyContractTest is Test {
    MyContract public myContract;

    address constant OWNER = address(1);
    address constant USER = address(2);

    function setUp() public {
        vm.prank(OWNER);
        myContract = new MyContract();
    }

    // Unit tests
    function test_Deposit() public { }

    // Edge cases
    function test_RevertWhen_ZeroDeposit() public { }

    // Fuzz tests
    function testFuzz_Deposit(uint256 amount) public { }

    // Invariant tests
    function invariant_TotalBalanceMatchesContract() public { }
}

Run tests:

forge test              # Run all tests
forge test -vvv         # Verbose output
forge test --gas-report # Include gas costs
forge coverage          # Coverage report

3. Security Analysis

Run comprehensive security checks:

# Static analysis with Slither
slither . --exclude-optimization --exclude-informational

# Linting with solhint
solhint 'src/**/*.sol' 'test/**/*.sol'

# Or use the automated script
bash scripts/check_security.sh

Pre-deployment checklist (from references/solidity-security.md):

• Reentrancy protection implemented
• Access controls on privileged functions
• Input validation on all external functions
• Emergency pause mechanism
• External calls follow CEI pattern
• Events emitted for state changes
• Gas optimizations applied
• Test coverage >90%
• Slither analysis passed
• solhint checks passed
• Professional audit for mainnet

4. Build and Deploy

Build contracts:

forge build --optimize --optimizer-runs 200

Deploy using script:

// script/Deploy.s.sol
import {Script} from "forge-std/Script.sol";
import {MyContract} from "../src/MyContract.sol";

contract DeployScript is Script {
    function run() external {
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
        vm.startBroadcast(deployerPrivateKey);

        MyContract myContract = new MyContract();
        console.log("Deployed at:", address(myContract));

        vm.stopBroadcast();
    }
}

Execute deployment:

# Load environment variables
source .env

# Simulate deployment
forge script script/Deploy.s.sol --rpc-url $SEPOLIA_RPC_URL

# Deploy to testnet
forge script script/Deploy.s.sol \
    --rpc-url $SEPOLIA_RPC_URL \
    --broadcast \
    --verify

# Deploy to mainnet (after audits!)
forge script script/Deploy.s.sol \
    --rpc-url $MAINNET_RPC_URL \
    --broadcast \
    --verify

Advanced Testing Patterns

Mainnet Forking

Test against real deployed contracts:

contract ForkTest is Test {
    IERC20 constant USDC = IERC20(0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48);

    function setUp() public {
        vm.createSelectFork("mainnet", 18_000_000);
    }

    function test_InteractWithRealProtocol() public {
        // Test with actual mainnet state
    }
}

forge test --fork-url $MAINNET_RPC_URL

Invariant Testing

Test properties that must always hold:

function invariant_SumOfBalancesEqualsTotalSupply() public {
    assertEq(token.totalSupply(), handler.sumOfBalances());
}

Fuzz Testing

Test with randomized inputs:

function testFuzz_Transfer(address to, uint256 amount) public {
    vm.assume(to != address(0));
    amount = bound(amount, 1, 1000 ether);
    // Test with random inputs
}

Gas Optimization

Key strategies from references/solidity-security.md:

1. Storage packing - Group uint8/uint16/etc in single slots
2. uint256 for counters - Native EVM word size
3. calldata over memory - For function parameters
4. Events over storage - Log data instead of storing
5. Custom errors - More gas-efficient than strings
6. Immutable/constant - For unchanging values

Contract Verification

# Verify on Etherscan
forge verify-contract $CONTRACT_ADDRESS \
    src/MyContract.sol:MyContract \
    --chain-id 1 \
    --etherscan-api-key $ETHERSCAN_KEY

# With constructor args
forge verify-contract $CONTRACT_ADDRESS \
    src/MyContract.sol:MyContract \
    --chain-id 1 \
    --etherscan-api-key $ETHERSCAN_KEY \
    --constructor-args $(cast abi-encode "constructor(uint256)" 100)

Common Commands Reference

Quick reference from references/foundry-commands.md:

Development:

forge build                    # Compile contracts
forge test                     # Run tests
forge test -vvv                # Verbose test output
forge coverage                 # Coverage report
forge fmt                      # Format code
forge clean                    # Clean artifacts

Testing:

forge test --match-test test_Transfer    # Run specific test
forge test --match-contract MyTest       # Run specific contract
forge test --gas-report                  # Show gas usage
forge test --fork-url $RPC_URL          # Fork testing
forge snapshot                           # Gas snapshot

Deployment:

forge script script/Deploy.s.sol --broadcast
forge create src/MyContract.sol:MyContract --rpc-url $RPC_URL
forge verify-contract $ADDRESS src/MyContract.sol:MyContract

Debugging:

forge test --debug test_MyTest           # Interactive debugger
cast run $TX_HASH --debug                # Debug transaction
cast run $TX_HASH --trace                # Trace transaction

Local node:

anvil                                    # Start local node
anvil --fork-url $MAINNET_RPC_URL       # Fork mainnet locally

Security Tools Integration

Slither

Static analyzer with 99+ vulnerability detectors:

slither .                                # Full analysis
slither . --exclude-optimization         # Skip optimizations
slither . --exclude-informational        # Critical issues only
slither . --checklist                    # Generate checklist

solhint

Linter configured via assets/solhint.config.json:

solhint 'src/**/*.sol'                   # Lint source
solhint 'test/**/*.sol'                  # Lint tests
solhint --fix 'src/**/*.sol'             # Auto-fix issues

Resources

references/

• solidity-security.md - Comprehensive security patterns, vulnerabilities, and mitigation strategies
• foundry-testing.md - Testing patterns including fuzzing, invariants, fork testing, and mocking
• foundry-commands.md - Complete command reference for forge, cast, and anvil

Best Practices Summary

1. Security First: Always implement CEI pattern, access controls, and input validation
2. Test Coverage: Aim for >90% coverage with unit, fuzz, and invariant tests
3. Static Analysis: Run Slither and solhint before every deployment
4. Gas Optimization: Apply after security, never at the expense of safety
5. Documentation: Use NatSpec comments for all public/external functions
6. Audit: Professional audit required for mainnet deployment
7. Verification: Verify all contracts on Etherscan post-deployment
8. Emergency: Include pause mechanisms for critical contracts

Common Patterns to Reference

When implementing specific functionality, reference these sections:

• ERC20 tokens - Use OpenZeppelin's implementation
• Access control - references/solidity-security.md (AccessControl, Ownable)
• Upgradeable contracts - OpenZeppelin's proxy patterns
• Reentrancy protection - references/solidity-security.md (CEI pattern)
• Testing external protocols - references/foundry-testing.md (fork testing)
• Gas optimization - references/solidity-security.md (optimization strategies)
• Randomness - Use Chainlink VRF, never block.timestamp alone
• Oracles - Use Chainlink price feeds for production

Workflow Example

Complete workflow for adding a new feature:

1. Write contract following security patterns
2. Write tests with >90% coverage
3. Run tests: forge test -vvv
4. Check coverage: forge coverage
5. Run Slither: slither .
6. Run solhint: solhint 'src/**/*.sol'
7. Format code: forge fmt
8. Build: forge build
9. Deploy to testnet: forge script script/Deploy.s.sol --broadcast
10. Verify: forge verify-contract ...
11. Get audit (for mainnet)
12. Deploy to mainnet after audit approval