Code Review Best Practices for Blockchain

When you’re building a blockchain application, a single line of flawed code can cost millions. Unlike traditional software, where you can push a patch overnight, blockchain code is immutable once deployed. If a smart contract has a漏洞, there’s no undo button. That’s why blockchain code review isn’t just a step in development-it’s the last line of defense.

Why Blockchain Code Review Is Different

Most software teams rely on automated scanners and quick peer reviews. That’s fine for a web app. But blockchain? It’s a different world. The value locked in smart contracts can reach billions. A bug that lets someone drain funds isn’t just a bug-it’s a heist waiting to happen.

Take The DAO hack in 2016. A single recursive call vulnerability let attackers steal $60 million worth of Ether. That incident didn’t just lose money. It shattered trust. Since then, every serious blockchain project treats code review like a security audit, not a code cleanup.

Unlike traditional apps, blockchain systems rely on consensus mechanisms, cryptographic signatures, and decentralized logic. A reviewer needs to understand how Ethereum’s EVM executes bytecode, how Solana’s fork-free consensus works, or how Cosmos handles cross-chain messages. Generic code review tools miss these nuances. You can’t scan for reentrancy attacks if your tool doesn’t know what a function call stack looks like in Solidity.

The Two Approaches: Bottom-Up vs. Top-Down

There are two main ways to review blockchain code, and they suit different experience levels.

The Bottom-Up Approach is for newcomers. Start with the smallest pieces: data structures, primitive types, and utility functions. For Ethereum clients, that means looking at reth-primitives first-how addresses, hashes, and numbers are defined. Then move to reth-evm to see how transactions are parsed and executed. After that, check reth-consensus for block validation logic. Finally, examine reth-engine-api for how the execution layer talks to the consensus layer. This method builds your mental model piece by piece. Sigma Prime recommends this path because it prevents overwhelm.

The Top-Down Approach is for veterans. Start at the entry points: public functions in smart contracts, API endpoints, or external contract calls. Trace execution paths like a depth-first search. Ask: Where does user input enter? Where does money leave? What happens if a function fails? This method catches logic flaws fast-like a contract that doesn’t check if a transfer succeeded before updating state.

Most teams use a hybrid: start top-down to find the high-risk areas, then drill down with bottom-up checks.

Automated Tools Aren’t Enough

You’ll hear people say, “Just run Slither or MythX.” And yes, those tools help. But they only catch about 30-40% of vulnerabilities, according to OWASP’s Code Review Guide v2. They’re great at spotting known patterns: reentrancy, integer overflows, unchecked external calls. But they can’t find logic flaws.

Imagine a token contract that lets users withdraw funds based on a timestamp. The developer thinks it’s safe because they check the time. But what if someone manipulates the block timestamp? Automated tools won’t catch that. Only a human who understands how miners control timestamps will.

Use tools like SonarQube, Veracode, or OWASP ZAP to automate the low-hanging fruit. But never trust them to find the dangerous stuff. Nethermind’s 2022 research showed that 73% of smart contract vulnerabilities were logical errors-exactly what automated scanners miss.

The Human Layer: Manual Review Must Lead

Manual review is non-negotiable. It’s slow. It’s expensive. But it’s the only way to catch business logic errors.

Here’s what a good manual review looks like:

• Trace every path a transaction can take through the contract.
• Ask: What happens if this function is called 100 times in one block?
• Check how errors are handled. Does the contract revert cleanly? Or does it leak stack traces?
• Verify all external calls use safe patterns: call().value() with proper checks, not transfer() alone.
• Look for race conditions. Is state updated before or after an external call?
• Test edge cases: zero values, max uint256, empty arrays, reentrant calls.

Sigma Prime’s engineers say LLMs can help with initial code understanding-but never for final approval. If a tool says “this looks fine,” trace it yourself. Always.

Checklist for a Solid Review

A good review isn’t random. It follows a checklist. Here’s what Devcom’s 2023 guidelines recommend:

• Input validation: Are all user inputs sanitized? Are arrays bounded? Are addresses checked for zero?
• Error handling: Does the contract fail safely? Are revert messages clear? Do they avoid leaking internal state?
• Authentication: Is access control properly enforced? Are roles defined? Is there a way to escalate privileges?
• API security: Are external contracts trusted? Are calls to unverified contracts allowed?
• Infrastructure: Is the node running on hardened servers? Are RPC endpoints rate-limited? Is TLS enforced?
• Data protection: Are sensitive values encrypted at rest? Is TDE or CLE used for on-chain data?

Update this checklist every time the codebase changes. A review done in January won’t catch a new vulnerability added in February.

Testing Beyond Unit Tests

Unit tests check if a function returns the right output. But blockchain needs more.

• Integration testing: Do multiple contracts work together? If Contract A calls Contract B, does B handle bad input from A?
• Fuzz testing: Feed random data into functions. Try 10,000 random inputs. Can it crash? Can it drain funds? Tools like Foundry’s fuzzing engine are built for this.
• Formal verification: This is the gold standard. Tools like Certora or CertiK use mathematical proofs to show a contract behaves correctly under all possible conditions. Nethermind predicts that by 2025, 60% of high-value contracts will use this.

A contract that passes unit tests but fails fuzz testing is a ticking bomb.

Who Should Review?

Not every developer can do this. Blockchain code review requires:

• Deep knowledge of the blockchain protocol (Ethereum, Solana, etc.)
• Experience writing or auditing smart contracts
• Understanding of common attack patterns (reentrancy, oracle manipulation, frontrunning)
• Patience to trace execution paths manually

Sigma Prime says it takes 6-12 months of focused training to become proficient. That’s why most serious teams hire third-party auditors. Firms like Halborn, Sigma Prime, and Certus Cybersecurity have built review frameworks specifically for blockchain. Enterprise adoption is up: 87% of enterprise blockchain projects now require a third-party audit before mainnet launch.

The Future: CI/CD and Regulation

Code review is moving into pipelines. OWASP found that 63% of blockchain teams now run automated scanners on every commit. That’s good-but not enough.

Regulations are catching up. The EU’s MiCA regulation, effective in 2024, requires crypto service providers to implement standardized security assessments-including code reviews. By 2026, 101Blockchains forecasts that 75% of enterprise blockchain projects will have mandatory review processes.

The message is clear: if you’re building on blockchain, you don’t get to skip this step. The cost of skipping it isn’t just technical-it’s reputational, legal, and financial.

Final Rule: Assume Everything Is Exploitable

The best blockchain reviewers operate with one mindset: if it can be broken, it will be broken. There’s no such thing as “probably safe.” There’s only “tested,” “verified,” and “deployed.”

Review like your life depends on it-because for someone, it might.