Blockchain Developer

Senior Solidity Engineer — Contract (Remote, UK) Contract length: 12 months Work mode: Remote — some overlap with US working hours required (client is US-based) Location: UK (applicants must be based in the UK / eligible to work in the UK) About the role We are seeking a Senior Solidity Engineer to join a fast-moving blockchain team focused on building secure, robust smart-contract systems for financial products. You will design, implement, test and maintain Solidity smart contracts, drive security best practices, and collaborate across frontend, backend and product teams to deliver production-grade decentralized systems. Key responsibilities • Design, develop, test and deploy Solidity smart contracts and related on-chain infrastructure. • Write and maintain unit, integration, fork and invariant tests to ensure long-term code quality. • Use Hardhat and/or Foundry for development, testing and deployments. • Perform and act on security reviews, threat models and on-chain vulnerability findings. • Integrate smart contracts with web3 frontends and backend services; collaborate closely with product managers and engineers. • Maintain and enhance existing contracts, handle live-contract incidents and issue remediation. • Keep up to date with cryptography, blockchain protocol changes and DeFi innovations; propose and implement improvements. • Communicate technical concepts clearly to both technical and non-technical stakeholders. Must-have skills & experience • Demonstrable hands-on experience developing Solidity smart contracts. • Strong understanding of blockchain security practices and common smart-contract vulnerabilities (reentrancy, integer over/underflows, access control, front-running, oracle manipulation, etc.). • Proficiency with Hardhat and Foundry. • Experience with Solidity security/static/fuzz testing tools such as Slither, Mythril and Echidna. • Practical scripting experience in JavaScript or TypeScript. • Strong experience writing unit, integration, fork and invariant tests. • Solid CS fundamentals — data structures, algorithms, and software engineering best practices. • Excellent debugging and troubleshooting skills. • Strong written and verbal communication in English; ability to explain technical issues to non-technical stakeholders. • Bachelor’s degree in Computer Science, Engineering, or related STEM discipline. • Development experience in banking/finance/trading or deep understanding of financial instruments and systems. Bonus / nice-to-have • Experience with financial infrastructure: collateral management, lending, balance-sheet systems. • Familiarity with Chainlink tools (CCIP, Data Feeds, VRF, Automation). • Multi-chain / cross-chain smart contract development experience. • Prior work with DeFi protocols (Aave, Uniswap, MakerDAO, etc.). • Experience with ZK (zero-knowledge) technologies. • Advanced STEM degree or blockchain/smart-contract certifications. Candidate profile • Senior, self-motivated engineer who thrives in a fast-paced environment. • Security-first mindset with a track record of shipping reliable on-chain systems. • Comfortable working remotely and coordinating across time zones (US/UK overlap).