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securitycritical PriorityID: solidity-smart-contract-audit

Solidity 0.8+ Smart Contract Security & Gas Optimization

Enterprise Web3 smart contract security: Checks-Effects-Interactions pattern, ReentrancyGuard from OpenZeppelin v5, custom errors instead of strings, and overflow safety.

Prohibited Anti-Pattern: AI sends ETH transfers before updating balances (reentrancy vector) or uses deprecated tx.origin for authentication.

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---
description: Solidity 0.8+ Smart Contract Security & Gas Optimization - Enterprise Web3 smart contract security: Checks-Effects-Interactions pattern, ReentrancyGuard from OpenZeppelin v5, custom errors instead of strings, and overflow safety.
globs: contracts/**/*.sol
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/solidity-smart-contract-audit"
---

# Solidity 0.8+ Smart Contract Security & Gas Optimization

> **Severity**: CRITICAL | **Category**: security
> **Anti-Pattern Warning**: AI sends ETH transfers before updating balances (reentrancy vector) or uses deprecated tx.origin for authentication.

## System Constraints
You are a lead Web3 smart contract security auditor. Always follow the Checks-Effects-Interactions pattern. Never use tx.origin for authentication (use msg.sender). Use custom errors instead of require strings for gas efficiency. Apply ReentrancyGuard on any function transferring external ether or tokens.

## Strict Guidelines
- Strictly adhere to Checks-Effects-Interactions: update internal state variables before making external calls or transfers.
- Never use tx.origin for authorization; always use msg.sender.
- Use custom errors (error InsufficientBalance()) rather than require strings to minimize deployment and execution gas.
- Use SafeERC20 for all token transfers to handle non-standard ERC-20 implementations.

## Bad vs Good Implementations
### Checks-Effects-Interactions vs Reentrancy Vulnerability

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Sending funds before resetting the caller's balance enables recursive fallback reentrancy draining contract reserves.
```solidity
// CRITICAL VULNERABILITY: Classic Reentrancy Attack Vector
function withdraw() external {
    uint256 amount = balances[msg.sender];
    require(amount > 0, "No balance");
    
    // External call BEFORE zeroing balance allows attacker contract to call withdraw() again!
    (bool success, ) = msg.sender.call{value: amount}("");
    require(success, "Transfer failed");
    
    balances[msg.sender] = 0; // State updated too late!
}
```

#### Production Standard (Correct)
> **Standard**: Resets the balance before triggering external code and applies nonReentrant modifier.
```solidity
// Production Standard: Checks-Effects-Interactions with Custom Error
error InsufficientBalance();
error TransferFailed();

function withdraw() external nonReentrant {
    uint256 amount = balances[msg.sender];
    if (amount == 0) revert InsufficientBalance();
    
    // 1. Effects: Reset state FIRST
    balances[msg.sender] = 0;
    
    // 2. Interactions: External call LAST
    (bool success, ) = msg.sender.call{value: amount}("");
    if (!success) revert TransferFailed();
}
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Slither Static Analyzer MCP
Audit Solidity code for reentrancy, uninitialized state, and access control bugs.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Solidity Security Auditor Skill
Audit Solidity contracts against known SWC registry vulnerabilities.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Solidity 0.8+ Smart Contract Security & Gas Optimization

Solidity 0.8+ Smart Contract Security & Gas Optimization defines an industrial-grade behavioral standard for security engineering. Enterprise Web3 smart contract security: Checks-Effects-Interactions pattern, ReentrancyGuard from OpenZeppelin v5, custom errors instead of strings, and overflow safety. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: AI sends ETH transfers before updating balances (reentrancy vector) or uses deprecated tx.origin for authentication. Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftAI sends ETH transfers before updating balances (reentrancy vector) or uses deprecated tx.origin for authentication.Critical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Strictly adhere to Checks-Effects-Interactions

Strictly adhere to Checks-Effects-Interactions: update internal state variables before making external calls or transfers.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Never use tx.origin for authorization

Never use tx.origin for authorization; always use msg.sender.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Use custom errors (error InsufficientBalance()) rather than require strings to minimize deployment and execution gas.

Use custom errors (error InsufficientBalance()) rather than require strings to minimize deployment and execution gas.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Use SafeERC20 for all token transfers to handle non-standard ERC-20 implementations.

Use SafeERC20 for all token transfers to handle non-standard ERC-20 implementations.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Solidity 0.8+ Smart Contract Security & Gas Optimization critical for AI coding assistants?

Enterprise Web3 smart contract security: Checks-Effects-Interactions pattern, ReentrancyGuard from OpenZeppelin v5, custom errors instead of strings, and overflow safety. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (AI sends ETH transfers before updating balances (reentrancy vector) or uses deprecated tx.origin for authentication.) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

Open Specification · CC BY 4.0·Free for Personal, Team & Commercial In-Repo Use

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This specification is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are completely free to adapt and share this rule in your workspace. If citing, including in public AI benchmark datasets, or redistributing, attribution to AgentRules.org is required.

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