Smart Contract Development Skill

CRITICAL RULES

1. Read reference files FIRST. When the user's request involves any topic in the reference table below, read those files before doing anything else — before writing code, before making decisions. Briefly mention which files you are reading so the user can confirm the skill is active (e.g., "Reading smart contracts reference...").
2. Information priority for VeChain topics: (a) Reference files in this skill — always the primary source. (b) VeChain MCP tools — use @vechain/mcp-server for on-chain data, transaction building, and live network queries; use Kapa AI MCP for VeChain documentation lookups. (c) Web search — only as a last resort, and only for topics NOT covered in the reference files.
3. Prefer working directly in the main conversation for VeChain tasks. Plan mode and subagents do not inherit skill context and may fall back to web search instead of using reference files.
4. After compaction or context loss, re-read this SKILL.md to restore awareness of the reference table and operating procedure before continuing work.

Scope

Use this Skill for Solidity smart contract development on VeChainThor:

• Solidity contracts with Hardhat + @vechain/sdk-hardhat-plugin
• ERC-20, ERC-721, access control, upgradeable (UUPS) patterns
• Gas optimization techniques
• Testing with Hardhat + Thor Solo
• Security reviews and audit checklists
• ABI codegen and TypeChain setup

Default stack

Layer	Default	Alternative
Contracts	Solidity + Hardhat + @vechain/sdk-hardhat-plugin	--
EVM target	paris (mandatory)	--
Testing	Hardhat + Thor Solo (--on-demand)	--
Types	TypeChain (@typechain/ethers-v6)	@vechain/vechain-contract-types (pre-built)
Node	Node 20 LTS (managed via nvm)	--

Operating procedure

1. Check Node version

Before installing dependencies or running any command:

• Check if .nvmrc exists in the project root. If yes, run nvm use to switch to the required version.
• If .nvmrc does not exist, create one with 20 (Node 20 LTS) and run nvm use.

2. Detect project structure

• turbo.json present → follow Turborepo conventions (packages/contracts, packages/*)

3. Clarify before implementing

When the user's request is ambiguous or could be solved multiple ways, ask before building. Separate research from implementation.

4. Implement with VeChain-specific correctness

• Network: always explicit (mainnet/testnet/solo)
• EVM target: always paris
• Gas: estimate first
• Tokens: VET for value, VTHO for gas (dual-token model)

5. Verify and deliver

A task is not complete until all applicable gates pass:

1. Code compiles — no build errors
2. Tests pass — existing tests still pass; new logic has test coverage
3. Risk notes documented — any signing, fee, or token-transfer implications are called out

Reference files

Read the matching files BEFORE doing anything else. See Critical Rules above.

Topic	File	Read when user mentions...
Smart contracts	references/smart-contracts.md	Solidity, Hardhat, ERC-20, ERC-721, deploy, contract interaction, libraries, contract size, upgradeable, proxy, upgrade, reinitializer, version pattern, deploy helpers, NatSpec, Slither
Gas optimization	references/smart-contracts-optimization.md	gas, optimize, storage packing, assembly, unchecked
Testing	references/testing.md	test, Thor Solo, Docker, CI, fixtures
ABI / codegen	references/abi-codegen.md	TypeChain, ABI, typechain-types, code generation
Security	references/security.md	security, audit, vulnerability, reentrancy, access control