Solidity / Web3 Engineer

About the Role Humanity Founders is looking for a skilled Solidity / Web3 Engineer to help build and scale the blockchain layer of our growing product ecosystem. You will own the smart contract architecture end-to-end — from writing and testing Solidity contracts to integrating them with the frontend via Web3.js, ensuring our on-chain systems are secure, efficient, and production-ready. Responsibilities • Design, develop, and deploy Solidity smart contracts on EVM-compatible networks • Build and maintain ERC-20 token infrastructure including staking, governance, and vesting mechanics • Integrate smart contracts with the frontend using Web3.js for wallet connections, contract reads/writes, and transaction handling • Implement DEX integrations using Uniswap V2/V3 for real token swaps and liquidity routing • Write comprehensive test suites using Hardhat and Chai, covering edge cases, reentrancy, overflow, and economic attack vectors • Collaborate with the Node.js backend team for ABI compatibility and event indexing • Conduct or coordinate security audits before any mainnet deployment Requirements • Proficient in Solidity 0.8.x with strong understanding of the EVM execution model • Hands-on experience with Web3.js for blockchain interaction (wallet integration, contract calls, event listening, transaction signing) • Experience with OpenZeppelin contracts (ERC20, Ownable, ReentrancyGuard, Upgradeable variants) • Practical experience integrating with Uniswap V2/V3 (swap routing, liquidity pools, price quoting) • Proficient in Hardhat for compiling, testing, deploying, and scripting contract interactions • Solid understanding of common smart contract vulnerabilities (reentrancy, integer overflow, oracle manipulation, front-running, flash loan attacks) • Familiarity with ABI encoding/decoding Tech Stack • Smart Contracts: Solidity 0.8.x • Blockchain Interaction: Web3.js, Ethers.js • Contract Framework: Hardhat • Contract Libraries: OpenZeppelin v5 • Testing: Hardhat Toolbox, Chai/Mocha • Optional: Uniswap V2/V3 Router, Viem Nice to Have • Experience with DeFi systems — perpetuals, margin trading, leverage, liquidation (e.g., GMX, dYdX) • Multi-chain deployment experience (Base, Arbitrum, Optimism) • Familiarity with security tools like Slither, Echidna, or Foundry • Gas optimization techniques and EVM storage best practices • Experience working in a monorepo with frontend and backend teams Contract & Payment Terms • Engaged as an independent contractor • Fully remote with flexible hours; • Competitive hourly rate: $30–$50/hour, based on experience • Payments made monthly via ACH/Wire About Humanity Founders Humanity Founders is a global technology company building scalable, high-performance digital products across mobile, web, and blockchain. We work with a cross-functional team of developers, designers, and product managers to ship impactful, user-focused solutions.