The Complete Smart Contract Developer Security Checklist: Build Safer, Audit-Ready Code in 2025

1. Code Architecture and Structure

Write clear modular code.

• Break complex logic into small, reusable functions: Each function should have a single, well-defined purpose. This improves readability, testability, and reduces the attack surface.
• Follow the Single Responsibility Principle: Keep contracts focused on one main functionality. Avoid monolithic contracts that handle multiple unrelated tasks.
• Implement proper separation of concerns: Separate data storage, business logic, and external interactions into distinct layers.
• Use descriptive variable and function names: Names should clearly indicate purpose and functionality without requiring additional documentation.
• Comment complex sections thoroughly: Document not just what the code does, but why specific design decisions were made. This helps auditors understand intent and identify potential issues.

2. Solidity Best Practices and Compiler Management

Stay current with Solidity versions

• Use the latest stable compiler version: As of 2025, Solidity v0.8.30 is the latest stable release, which includes maintenance updates for the Pectra Ethereum network upgrade
• Enable all compiler warnings: Use strict compilation settings to catch potential issues early
• Specify exact compiler versions: Pin specific versions in your pragma statements for reproducible builds

Implement robust error handling.

• Leverage built-in overflow protection: Solidity 0.8+ includes automatic overflow/underflow checks, eliminating the need for SafeMath in most cases
• Use require() for input validation: Check preconditions and user inputs
• Use assert() for internal invariants: Check conditions that should never be false in correct code
• Implement custom errors for gas efficiency: Custom errors use less gas than string-based error messages

3. Access Control and Permission Management

Implement Robust Access Controls

• Use OpenZeppelin’s AccessControl or Ownable patterns: These battle-tested libraries provide secure access control mechanisms
• Avoid hardcoding addresses: Make ownership and privileged roles transferable and updatable
• Implement role-based permissions: Use granular permissions rather than single-owner models where appropriate
• Add time delays for critical operations: Implement timelock mechanisms for sensitive administrative functions

Test Administrative Functions Extensively

• Test all admin function combinations: Ensure admin functions can’t be chained to bypass security measures
• Implement emergency pause mechanisms: Include circuit breakers that can halt operations during emergencies
• Document all privileged operations: Clearly document what each admin function can do and its potential impact

4. Financial Security and Fund Management

Prevent Reentrancy Attacks

• Follow the checks-effects-interactions pattern: Always update state before making external calls
• Use OpenZeppelin’s ReentrancyGuard: Add the nonReentrant modifier to functions that handle funds
• Minimize external calls: Reduce the number of external contract interactions
• Be cautious with fallback functions: Avoid complex logic in receive() and fallback() functions

Implement Secure Payment Patterns

• Prefer pull payments over push payments: Let users withdraw funds rather than automatically sending them
• Use withdrawal patterns for bulk payments: Implement withdrawal queues for scenarios requiring multiple payments
• Implement proper fund isolation: Separate user funds from protocol funds and operational funds
• Add withdrawal limits and cooldowns: Implement rate limiting for large withdrawals

5. Upgradability and Deployment Strategy

Plan Your Upgrade Strategy Early

• Decide on upgradability before development: Choose between immutable contracts, proxy patterns, or modular architectures
• Document upgrade procedures clearly: If using upgradeable contracts, document the upgrade process and governance
• Implement proper initialization: Use initializer functions instead of constructors for upgradeable contracts
• Plan for emergency upgrades: Have procedures for rapid response to critical vulnerabilities

Proxy Pattern Considerations

• Use established proxy patterns: OpenZeppelin’s upgradeable contracts or Diamond Standard
• Understand storage layout constraints: Prevent storage collisions between implementation versions
• Implement upgrade governance: Require multisig or DAO approval for upgrades
• Test upgrade scenarios: Verify that upgrades work correctly and don’t break existing functionality

6. Gas Optimization and Efficiency

Optimize Storage Operations

• Minimize storage writes: Storage operations are the most expensive EVM operations
• Pack struct variables efficiently: Use appropriate data types to fit multiple variables in single storage slots
• Use memory for temporary data: Prefer memory over storage for intermediate calculations
• Implement efficient data structures: Choose appropriate mappings, arrays, and structs for your use case

Event and Data Management

• Use events for off-chain data: Store frequently accessed but non-critical data in events rather than storage
• Implement efficient search patterns: Use indexed event parameters for filtering
• Batch operations when possible: Combine multiple operations into single transactions where feasible
• Optimize loop operations: Avoid unbounded loops and implement proper gas limit checks

7. Comprehensive Testing Strategy

Unit Testing Requirements

• Test every public and external function: Ensure complete function coverage
• Include edge cases in testing: Test with zero values, maximum values, and boundary conditions
• Test failure scenarios: Verify that functions fail gracefully with appropriate error messages
• Use property-based testing: Implement invariant testing to catch unexpected behaviors

Integration Testing

• Test external protocol interactions: Verify behavior when interacting with other smart contracts
• Use mainnet forking for realistic testing: Test against actual deployed contracts and real data
• Simulate network conditions: Test behavior under high gas prices and network congestion
• Test upgrade scenarios: If upgradeable, test the upgrade process thoroughly

Advanced Testing Tools

• Fuzzing with Echidna or Foundry: Use property-based fuzzing to discover edge cases
• Static analysis with Slither: Automated detection of common vulnerability patterns
• Formal verification for critical functions: Mathematical proofs of correctness for high-value operations
• Gas optimization testing: Benchmark gas usage and optimize expensive operations

8. External Integration Security

Oracle and Price Feed Security

• Use multiple oracle sources: Implement price feed aggregation to prevent single points of failure
• Add price validation mechanisms: Check for unrealistic price movements and implement circuit breakers
• Implement time-weighted average prices (TWAP): Reduce vulnerability to flash loan attacks
• Add oracle freshness checks: Ensure price data is recent and valid

Cross-Protocol Interactions

• Validate external contract interfaces: Ensure external contracts implement expected interfaces correctly
• Handle external call failures gracefully: Implement proper error handling for external contract calls
• Use pull patterns for external data: Avoid relying on external contracts pushing data to your contract
• Implement protocol-specific security measures: Understand and mitigate risks specific to protocols you interact with

9. Documentation and Code Quality

Comprehensive Documentation Requirements

• Write detailed README files: Include project overview, architecture decisions, and deployment instructions
• Document all external interfaces: Provide clear documentation for all public functions and their parameters
• Explain critical business logic: Document complex algorithms and economic mechanisms
• Include deployment and configuration guides: Provide step-by-step deployment instructions

Code Quality Standards

• Use consistent coding style: Follow established Solidity style guides
• Implement proper error messages: Provide clear, actionable error messages for users
• Add inline comments for complex logic: Explain non-obvious code sections
• Include function specifications: Document preconditions, postconditions, and side effects

10. Pre-Audit Preparation and Security Scanning

Automated Security Analysis

• Run static analysis tools: Use Slither, MythX, or Securify to identify common vulnerabilities
• Perform manual code review: Have experienced developers review the code for logic issues
• Check for known vulnerability patterns: Review OWASP Smart Contract Top 10 and similar resources
• Validate against security checklists: Use established security checklists like ConsenSys’s

Repository and Code Organization

• Clean up development artifacts: Remove test files, commented code, and unused dependencies
• Organize code logically: Structure files and directories clearly for auditor review
• Include comprehensive test suite: Provide tests that demonstrate all functionality works correctly
• Prepare audit documentation: Create documents explaining architecture, known limitations, and areas of concern