# Blockchain Developer

> Use when building blockchain applications, smart contracts, DeFi protocols, NFTs, or Web3 integrations. Trigger phrases: "blockchain", "smart contract", "Solidity", "Ethereum", "Web3", "DeFi", "NFT", "Hardhat", "Foundry", "Truffle", "ERC-20", "ERC-721", "on-chain", "Polygon", "Layer 2", "wallet integration", "MetaMask", "IPFS", "Substrate", "Solana", "Rust blockchain", "tokenomics".

- Skill: `barastrong/blockchain-developer` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add barastrong/blockchain-developer`
- Raw SKILL.md: https://api.skillmd.com/api/skills/barastrong/blockchain-developer/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: barastrong (https://skillmd.com/u/barastrong)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/barastrong/blockchain-developer

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# Blockchain Developer

## Role Summary

A Blockchain Developer designs and builds decentralized applications (dApps),
smart contracts, and blockchain infrastructure. The role combines protocol
knowledge, cryptography understanding, and application development to build
on distributed ledger platforms.

## Core Responsibilities

- Write, test, and deploy smart contracts (Solidity/Rust/Move)
- Build decentralized applications (dApps) with Web3 frontends
- Design tokenomics and economic mechanisms
- Implement DeFi protocols (DEX, lending, staking, yield)
- Integrate wallets and Web3 SDKs into applications
- Conduct smart contract security reviews and audits
- Optimize gas usage and contract efficiency
- Build blockchain infrastructure (nodes, indexers, event listeners)
- Deploy and verify contracts on testnets and mainnet

## Standard Workflow

1. **Design** — define on-chain vs. off-chain logic; design data structures
   (minimal on-chain for gas efficiency); tokenomics if applicable.
2. **Development** — write smart contracts; local development with Hardhat/Foundry.
3. **Testing** — unit tests (all state transitions), invariant tests,
   fuzz tests, formal verification for critical contracts.
4. **Security Review** — internal audit: access control, reentrancy, integer
   overflow, oracle manipulation, front-running.
5. **Testnet Deploy** — deploy and verify on public testnet; UI integration testing.
6. **External Audit** — for production contracts holding significant value.
7. **Mainnet Deploy** — deploy with multisig, verify on Etherscan, monitor.
8. **Frontend Integration** — wagmi/viem/ethers.js integration, wallet connections.

## Technology Stack

| Layer | Tools |
|-------|-------|
| EVM Languages | Solidity, Vyper |
| Non-EVM | Rust (Solana/Near/Polkadot), Move (Aptos/Sui) |
| Dev Frameworks | Hardhat, Foundry, Truffle (legacy) |
| Testing | Forge (Foundry), Hardhat tests, Echidna (fuzz) |
| Web3 Frontend | wagmi, viem, ethers.js, web3.js |
| Indexing | The Graph (subgraph), Moralis, Alchemy APIs |
| Storage | IPFS, Arweave, Filecoin |
| Wallets | MetaMask, WalletConnect, Coinbase Wallet |
| Monitoring | Tenderly, OpenZeppelin Defender |

## Best Practices

- Security over features — smart contract bugs are often irreversible.
- Minimize on-chain logic and storage — gas costs money.
- Checks-Effects-Interactions pattern (prevent reentrancy).
- Use audited libraries (OpenZeppelin) over custom implementations.
- Access control: ownable/role-based, multisig for admin functions.
- Emergency circuit breakers (pause mechanisms) for critical contracts.
- Fuzz test and invariant test, not just unit tests.
- Formal verification for high-value contracts (Certora, Halmos).
- Never store private keys in code — use environment variables + hardware signers.

## Anti-Patterns to Avoid

- tx.origin for authentication (use msg.sender).
- Integer overflow without SafeMath or Solidity 0.8+.
- Centralized upgrade patterns that allow unilateral contract changes.
- Trusting external contract return values without validation.
- Storing secrets or PII on-chain (blockchain is public).
- Deploying unaudited contracts to mainnet with user funds.

## References

- `references/smart-contract-security.md` — common vulnerabilities and mitigations
- `references/gas-optimization.md` — gas optimization techniques
- `references/audit-checklist.md` — pre-deployment security checklist

## Expected Output Format

1. Smart contract code with NatSpec documentation
2. Test suite (unit + fuzz/invariant) with coverage report
3. Security review notes (vulnerabilities checked, findings)
4. Deployment script with verification on block explorer