Blockchain & Web3 Development Skill — Quick Reference

This skill equips blockchain developers with execution-ready patterns for building secure, gas-optimized smart contracts and decentralized applications. Claude should apply these patterns when users ask for smart contract development, DeFi protocols, NFT implementations, security audits, or Web3 architecture.

Modern Best Practices (December 2025): Security-first development, formal verification, comprehensive testing (unit, integration, fork, invariant), gas optimization, upgradeable contracts, multi-chain deployment, and battle-tested DeFi patterns. Tools: Foundry 1.5 (npm packages, improved fuzzer), Hardhat 3 (Solidity tests, Rust performance, multichain), Solidity 0.8.31 (Fusaka upgrade, ARM Linux builds).

Quick Reference

When to Use This Skill

Claude should invoke this skill when a user requests:

• Smart contract development (Solidity, Rust, CosmWasm)
• DeFi protocol implementation (AMM, lending, staking, yield farming)
• NFT and token standards (ERC20, ERC721, ERC1155, SPL tokens)
• DAO governance systems
• Cross-chain bridges and interoperability
• Gas optimization and storage patterns
• Smart contract security audits
• Testing strategies (Foundry, Hardhat, Anchor)
• Oracle integration (Chainlink, Pyth)
• Upgradeable contract patterns (proxies, diamonds)
• Web3 frontend integration (ethers.js, web3.js, @solana/web3.js)
• Blockchain indexing (The Graph, subgraphs)
• MEV protection and flashbots
• Layer 2 scaling solutions (Optimism, Arbitrum, zkSync)
• Backend crypto integration (.NET/C#, multi-provider architecture, CQRS)
• Webhook handling and signature validation (Fireblocks, custodial providers)
• Event-driven architecture with Kafka for crypto payments
• Transaction lifecycle management and monitoring
• Wallet management (custodial vs non-custodial)

Decision Tree: Blockchain Platform Selection

Project needs: [Use Case]
    ├─ EVM-compatible smart contracts?
    │   ├─ Complex testing needs → Foundry (Solidity tests, fuzzing, gas snapshots)
    │   ├─ TypeScript ecosystem → Hardhat (plugins, TypeScript, Ethers.js)
    │   └─ Enterprise features → NestJS + Hardhat
    │
    ├─ High throughput/low fees?
    │   ├─ Rust-based → Solana (Anchor framework, 50k+ TPS)
    │   ├─ EVM L2 → Arbitrum/Optimism (Ethereum security, lower gas)
    │   └─ Telegram integration → TON (Tact/FunC contracts)
    │
    ├─ Interoperability across chains?
    │   ├─ Cosmos ecosystem → CosmWasm (IBC protocol)
    │   ├─ Multi-chain DeFi → LayerZero or Wormhole
    │   └─ Bridge development → Custom bridge contracts
    │
    ├─ Token standard implementation?
    │   ├─ Fungible tokens → ERC20 (OpenZeppelin), SPL Token (Solana)
    │   ├─ NFTs → ERC721/ERC1155 (OpenZeppelin), Metaplex (Solana)
    │   └─ Semi-fungible → ERC1155 (gaming, fractionalized NFTs)
    │
    ├─ DeFi protocol development?
    │   ├─ AMM/DEX → Uniswap V3 fork or custom (x*y=k, concentrated liquidity)
    │   ├─ Lending → Compound/Aave fork (collateralized borrowing)
    │   └─ Staking/Yield → Custom reward distribution contracts
    │
    ├─ Upgradeable contracts required?
    │   ├─ Transparent Proxy → OpenZeppelin (admin/user separation)
    │   ├─ UUPS → Gas-efficient (upgrade logic in implementation)
    │   └─ Diamond Standard → Modular functionality (EIP-2535)
    │
    └─ Backend integration?
        ├─ .NET/C# → Multi-provider architecture (see Backend Integration Patterns)
        ├─ Node.js → Ethers.js/Web3.js + Prisma
        └─ Python → Web3.py + FastAPI

Chain-Specific Considerations:

• Ethereum/EVM: Security-first, higher gas costs, largest ecosystem
• Solana: Performance-first, Rust required, lower fees
• Cosmos: Interoperability-first, IBC native, growing ecosystem
• TON: Telegram-first, async contracts, unique architecture

See resources/ for chain-specific best practices.

Navigation

Resources

• resources/blockchain-best-practices.md — Universal blockchain patterns and security
• resources/backend-integration-best-practices.md — .NET/C# crypto integration patterns (CQRS, Kafka, multi-provider)
• resources/solidity-best-practices.md — Solidity/EVM-specific guidance
• resources/rust-solana-best-practices.md — Solana + Anchor patterns
• resources/cosmwasm-best-practices.md — Cosmos/CosmWasm guidance
• resources/ton-best-practices.md — TON contracts (Tact/Fift/FunC) and deployment
• ../software-security-appsec/resources/smart-contract-security-auditing.md — Smart contract audit workflows and tools (see software-security-appsec skill)
• README.md — Folder overview and usage notes
• data/sources.json — Curated external references per chain

Templates

• Ethereum/EVM: templates/ethereum/template-solidity-hardhat.md, templates/ethereum/template-solidity-foundry.md
• Solana: templates/solana/template-rust-anchor.md
• Cosmos: templates/cosmos/template-cosmwasm.md
• TON: templates/ton/template-tact-blueprint.md, templates/ton/template-func-blueprint.md
• Bitcoin: templates/bitcoin/template-bitcoin-core.md

Related Skills

• ../software-security-appsec/SKILL.md — Security hardening, threat modeling, OWASP vulnerabilities
• ../software-architecture-design/SKILL.md — System decomposition, modularity, dependency design
• ../ops-devops-platform/SKILL.md — Infrastructure, CI/CD, observability for blockchain nodes
• ../software-backend/SKILL.md — API integration with smart contracts, RPC nodes, indexers
• ../qa-resilience/SKILL.md — Resilience, circuit breakers, retry logic for chains
• ../software-code-review/SKILL.md — Code review patterns and quality gates
• ../dev-api-design/SKILL.md — RESTful design for Web3 APIs and dApp backends

Operational Playbooks

• resources/operational-playbook.md — Smart contract architecture, security-first workflows, and platform-specific patterns