Perfect Practices for Conducting a Solidity Audit

Deploying a smart contract in an environment as dynamic as Web3 isn’t just about bringing your vision to life, but rather making sure it stands up to the toughest scrutiny.

That’s where a Solidity audit comes in. Forget the idea of audits as stuffy paperwork. In blockchain, it’s the thorough check that ensures your project won’t crumble under pressure.

Let’s explore the best practices that turn a Solidity audit from a simple checklist into a bulletproof shield for your code.

Code Feedback: The Heart of a Solidity Audit Code Feedback and Static Analysis

The foundation of any effective Solidity audit is a high-quality Manual Code Review. Even though automated tools can assist, it is the expertise and judgment of experienced auditors that make the difference between a superficial scan and a deep, meaningful security review.A Solidity audit’s first line of defense is a thorough code review combined with static analysis. This process comprises:

Manual Code Feedback

This process comprises the scrutiny of smart contract code line by line, with a focus on:

• Identifying logical errors and flaws in the contract’s architecture;
• Spotting insecure coding patterns and anti-patterns that could introduce vulnerabilities;
• Detecting deviations from industry best practices that might lead to reliability or security issues;
• Understanding the contract’s intended business logic, ensuring the implemented behavior matches expectations.

Manual review also allows auditors to reason about complex interactions and contextual risks, things automated tools simply cannot catch.

Supporting with Static Analysis (Where Useful)

Even though a Manual Code Review remains the primary audit method, tools like Slither or Mythril can complement the process by providing additional automated checks. These tools help identify common vulnerabilities such as reentrancy, integer overflows, or unchecked external calls, though they should never replace manual expertise.

If you combine a rigorous manual review with a selective use of static analysis tools, you can maximize your chances of catching both surface-level issues and subtle, business-logic flaws.

• Manual Code Review: Scrutinizing the code line-by-line to identify logical errors, insecure coding patterns, and deviations from best practices;
• Static Analysis Tools: Utilizing tools like Slither, Mythril, and SmartCheck to automatically detect vulnerabilities such as reentrancy, integer overflows, and unchecked external calls. These tools analyze the code without executing it, providing insights into potential security flaws.

By combining manual reviews with automated tools, you can catch a wide array of issues early in the development cycle.

Testing for Security Vulnerabilities

Testing is not about running every tool available; it is, in fact, about ensuring your contract behaves as expected under both normal and adversarial conditions. Automated tools can assist, but quality test design and a deep understanding of the code are key:

• Unit Testing: Write exhaustive tests for each function to ensure they behave as expected under various conditions;
• Integration Testing: Test how different parts of your contract interact with each other and with external contracts or systems;
• Fuzz Testing: Employ tools like Echidna to generate random inputs and test for unexpected behaviors or crashes;
• Test Coverage Analysis: Use tools like Forge Coverage to identify untested parts of your codebase, ensuring no stone is left unturned.

Remember that the goal is not just to test for expected outcomes but to anticipate and handle unexpected scenarios gracefully.

Understanding Solidity-Specific Risks

Even with Solidity 0.8 and above reverting on integer overflow/underflow by default, there are still edge cases to watch out for:Solidity, while powerful, has its quirks and pitfalls. Awareness of these is vital:

• Silent Overflows via Type Casting: Converting a larger type to a smaller one (e.g., uint256 → uint8) can wrap values without triggering a revert. Example: casting 256 to uint8 results in 0 silently; Reentrancy Attacks: These occur when an external contract calls back into the calling contract before the first invocation is complete, potentially leading to unexpected behavior or fund loss;
• Integer Overflows/Underflows: In Solidity ≥0.8.0, regular arithmetic operations revert on overflow/underflow. However, edge cases still exist, such as type conversions to smaller types, unchecked shift operations, unchecked blocks, or inline assembly. These scenarios can silently wrap values and should be carefully audited;Arithmetic operations that exceed the maximum or minimum limits of a data type can lead to incorrect calculations;
• Unchecked Shifts: The << and >> bit‑shift operators aren’t protected by Solidity’s overflow/underflow checks. Excessive shifts can wrap values unexpectedly;Gas Limit and Loops: Unbounded loops can consume excessive gas, leading to failed transactions;
• Unchecked Blocks & Inline Assembly: Developers can explicitly disable safety checks using unchecked { … }, which allows wrapping behavior, or use Yul/inline assembly, neither of which includes built-in overflow protection.Timestamp Dependence: Relying on block timestamps for critical logic can be manipulated by miners to some extent.

Staying updated with the latest Solidity versions and understanding these risks can help in writing more secure contracts.

Documentation and Version Control

Clear documentation and robust version control are the unsung heroes of a successful Solidity audit:

• Comprehensive Documentation: Maintain detailed documentation of your contract’s architecture, functions, and intended behaviors. This aids auditors in understanding the contract’s purpose and logic;
• Version Control Systems: Use systems like Git to track changes, manage different versions, and collaborate effectively. Tagging specific commits for audit purposes ensures clarity on what code was reviewed;
• Change Logs: Keep a log of post-audit changes to maintain a clear history and facilitate future audits.

Proper documentation and version control not only streamline the audit process but also enhance the maintainability of your codebase.

Additional Perfect Practices

Beyond the core areas, consider these practices to bolster your contract’s security:

Utilize Established Libraries

Take advantage of well-audited libraries for common functionalities such as token standards, access control, and safe math operations. This reduces the risk of introducing vulnerabilities in custom implementations.

Implement Access Controls

Ensure that sensitive functions are protected using modifiers like onlyOwner or role-based access controls, as this prevents unauthorized interactions with critical parts of your contract.

Avoid Using tx.origin for Authentication

Recent updates to Ethereum’s EVM via the Pectra upgrade (activated May 7, 2025)—specifically EIP‑7702—have fundamentally changed the assumptions behind using tx.origin for security checks.

Here’s what you need to know:Using tx.origin can expose your contract to phishing attacks. Instead, rely on msg.sender to verify the caller’s identity.

• Pectra enables code execution by EOAs (Externally Owned Accounts): With EIP‑7702, EOAs can now deploy temporary bytecode to themselves using the new SET_CODE_TX_TYPE, meaning a single key address can behave like a smart contract during execution;

• tx.origin == msg.sender is no longer a reliable check: Contracts previously used this check to ensure the caller was an EOA, and to prevent reentrancy or flash‑loan contracts, but now, even if msg.sender equals tx.origin, that address may hold executable code. The old assumption “EOAs don’t execute code” is broken;

Why this matters:

• Bypassed reentrancy protection: Contracts using require(tx.origin == msg.sender) to block reentrant calls can now be tricked via EOA-delegated code;
• Broken flash-loan shields: Some teams relied on the same pattern to prevent contract-driven flash-loan attacks, but this pattern no longer effectively blocks them.

Recommended Fix

• Avoid using tx.origin == msg.sender for any kind of authentication or security logic;
• Use proper reentrancy guards (like OpenZeppelin’s ReentrancyGuard) and rely on msg.sender or contract-specific roles for secure access control;
• Address any legacy code that depends on EOA assumptions prior to Pectra to avoid hidden vulnerabilities.

Final Thoughts

Conducting a thorough Solidity audit is, more than a mere best practice, a necessity in the decentralized ecosystem.

If you combine meticulous code reviews, exhaustive testing, awareness of Solidity-specific risks, and diligent documentation, you can fortify your smart contracts against potential threats.

Remember that security is an ongoing process, and as such, regular audits, continuous monitoring, and staying informed about emerging vulnerabilities are key to maintaining trust and integrity in your decentralized applications.