Protocol Engineer, San Francisco

Capital markets are undergoing a fundamental shift. Assets that live in fragmented systems and manual workflows are moving onto blockchains -systems designed to move and store value more transparently and efficiently.

While this unlocks more open and programmable financial systems, it also introduces significant complexity. For most users, interacting with this new infrastructure is still too difficult.

Fun builds the infrastructure that powers consumer-facing fintech applications - handling onboarding, account access, and money movement so users can interact with blockchain-based systems as seamlessly as they do with traditional finance.

For fintech builders, Fun provides a best-in-class onboarding and deposit stack that drives conversion and unlocks user growth. We operate at the intersection of financial infrastructure, complex engineering, and product experience.

Role Overview We're looking for a Protocol Engineer to join our core blockchain team and help build the foundation of Web3 payments infrastructure. This high-impact role offers the opportunity to work on challenging technical problems at the intersection of smart contracts, cross-chain protocols, and decentralized finance.

You will design and implement secure, efficient smart contract systems and blockchain integrations that power millions of transactions across multiple chains. This role is perfect for a technically strong engineer who thrives in fast-paced environments and wants to shape the future of decentralized finance.

Responsibilities • Design, develop, and deploy secure smart contracts and protocol implementations across multiple blockchain platforms

• Collaborate with backend and product teams to architect blockchain solutions that meet business requirements

• Write highly efficient, well-tested code and participate in security audits to ensure protocol safety

• Research and evaluate new blockchain technologies, protocols, and DeFi primitives for integration opportunities

• Contribute to incident response and debugging on-chain issues to ensure protocol reliability

Requirements • Strong experience building and deploying production smart contracts on major blockchain platforms

• Deep understanding of blockchain architecture, consensus mechanisms, and cryptographic principles

• Hands-on experience with smart contract development languages (Solidity, Rust, Move, etc.)

• Solid grasp of DeFi protocols, token standards, and cross-chain communication patterns

• Strong security mindset with knowledge of common smart contract vulnerabilities and best practices

• Clear communicator who can explain complex blockchain concepts to cross-functional teams

Nice to Have • Production experience with multiple blockchain ecosystems (Ethereum, Solana, L2s, etc.)

• Previously worked at crypto startup or Web3 infrastructure company

• Experience with cross-chain bridges, oracles, or interoperability protocols

• Background with high-volume DeFi protocols or DEX infrastructure

• Contributions to blockchain open source projects or protocol research

• Experience with formal verification or advanced smart contract testing frameworks