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. Apply these patterns when you need smart contract development, DeFi protocols, NFT implementations, security audits, or Web3 architecture.

Modern Best Practices (Jan 2026): Solidity 0.8.33+, security-first development, explicit threat models, comprehensive testing (unit, integration, fork, invariant), audits/formal methods where warranted, upgrade safety (timelocks, governance, rollback plans), and defense-in-depth for key custody and signing.

Quick Reference

When to Use This Skill

Use this skill when you need:

• 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)
    │   ├─ 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.

Security-First Patterns (Jan 2026)

Security baseline: Assume an adversarial environment. Treat contracts and signing infrastructure as public, attackable APIs.

Custody, Keys, and Signing (Core)

Key management is the dominant risk driver in production crypto systems. Use general key management guidance as a baseline (NIST SP 800-57) https://csrc.nist.gov/publications/detail/sp/800-57-part-1/rev-5/final

Do:

• Separate hot/warm/cold signing paths with limits and approvals [Inference]
• Require dual control for high-value transfers (policy engine + human approval) [Inference]
• Keep an immutable audit trail for signing requests (who/what/when/why) [Inference]

Avoid:

• Storing private keys in databases or application config
• Reusing signing keys across environments (dev/staging/prod)
• Hot-wallet automation without rate limits and circuit breakers [Inference]

Checks-Effects-Interactions (CEI) Pattern

Mandatory for all state-changing functions.

// Correct: CEI pattern
function withdraw(uint256 amount) external {
    // 1. CHECKS: Validate conditions
    require(balances[msg.sender] >= amount, "Insufficient balance");

    // 2. EFFECTS: Update state BEFORE external calls
    balances[msg.sender] -= amount;

    // 3. INTERACTIONS: External calls LAST
    (bool success, ) = msg.sender.call{value: amount}("");
    require(success, "Transfer failed");
}

// Wrong: External call before state update (reentrancy risk)
function withdrawUnsafe(uint256 amount) external {
    require(balances[msg.sender] >= amount);
    (bool success, ) = msg.sender.call{value: amount}("");
    require(success);
    balances[msg.sender] -= amount; // Too late!
}

Formal Verification

// Certora CVL rule example
rule balanceNeverNegative(address user) {
    env e;
    require balances[user] >= 0;
    deposit(e);
    assert balances[user] >= 0;
}

MEV Protection

// Commit-reveal pattern
mapping(address => bytes32) public commitments;

function commit(bytes32 hash) external {
    commitments[msg.sender] = hash;
}

function reveal(uint256 value, bytes32 salt) external {
    require(
        keccak256(abi.encodePacked(value, salt)) == commitments[msg.sender],
        "Invalid reveal"
    );
    // Process revealed value
}

Optional: AI/Automation Extensions

Note: AI-assisted smart contract tools. Skip if not using AI tooling.

AI-Assisted Auditing

LLM Limitations in Smart Contracts

Do not rely on LLMs for:

• Security-critical logic verification
• Gas optimization calculations
• Complex mathematical proofs

Use LLMs for:

• Boilerplate generation (tests, docs)
• Code explanation and review prep
• Initial vulnerability hypotheses (verify manually)

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
• Shared secure review checklist: ../software-clean-code-standard/templates/checklists/secure-code-review-checklist.md

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