Smart Contract Vulnerability Checker
Paste your smart contract code below to check for common vulnerabilities. This tool analyzes for critical issues mentioned in the article: reentrancy, access control flaws, and arithmetic errors. Remember: automated tools catch only 30-40% of vulnerabilities. Always conduct thorough manual reviews.
One line of faulty code in a blockchain smart contract can wipe out millions. Unlike traditional software, you can't just push a patch when something breaks. Once deployed, blockchain code is permanent. That’s why blockchain code review isn’t just a good idea-it’s the only thing standing between a project and disaster.
Why Blockchain Code Review Is Different
Traditional code reviews focus on readability, performance, and maintainability. Blockchain code reviews? They’re about survival. A single logic error in a DeFi contract can let attackers drain funds. The DAO hack in 2016 stole $60 million because of a reentrancy bug. The Poly Network hack in 2021 lost $610 million due to a flawed access control check. These weren’t random glitches. They were preventable mistakes that slipped through inadequate reviews. The core difference? Immutability. In regular apps, you fix bugs. In blockchain, you can’t. Once the contract is live, it’s on the ledger forever. That means every line of code must be flawless before deployment. Automated tools catch only 30-40% of vulnerabilities, according to OWASP. The rest? They need human eyes.The Two Approaches: Bottom-Up vs. Top-Down
There are two main ways to review blockchain code. Which one you use depends on your experience level. Bottom-Up is for beginners. Start small. Look at the basic data structures first-things like how addresses are stored, how tokens are transferred, how numbers are calculated. In Ethereum clients like reth, that means checkingreth-primitives before touching reth-evm (the execution layer), then reth-consensus (how blocks are validated), and finally reth-engine-api (how clients talk to each other). You’re building a foundation. If the basics are broken, nothing above them is safe.
Top-Down is for experts. Start at the entry points: the public functions anyone can call. Trace how data flows through the contract. Follow every path: what happens if someone sends 0 ETH? What if they spam calls? What if they manipulate timestamps? Think like an attacker. Use call graphs to map execution paths like a depth-first search. This approach finds complex logic flaws automated tools miss-like improper access control or unchecked external calls.
Must-Have Tools: Automated and Manual
Never rely on just one method. Use both automated tools and manual review. Automated tools are your first line of defense. Use SonarQube for general code smells, Veracode for static analysis, and Burp Suite or OWASP ZAP for API and endpoint testing. These tools flag common issues: unguarded external calls, integer overflows, missing access controls. But here’s the catch: they can’t understand intent. They don’t know if a function is supposed to be public or private. They can’t spot a cleverly disguised reentrancy pattern hidden behind multiple layers of abstraction. That’s where manual review comes in. Manual review means reading every line. Not skimming. Not scanning. Reading. Ask yourself: What happens if this variable is negative? What if the sender is a contract? What if this function is called during a reorg? Use a debugger to step through execution. Trace state changes. Simulate edge cases. This is slow. It’s tedious. But it’s the only way to catch what machines can’t.The Smart Contract Checklist
Every blockchain code review should follow a strict checklist. Here’s what to verify:- Input validation: Are all user inputs sanitized? Can someone pass a zero value, a negative number, or a malformed address?
- Access control: Are only authorized addresses allowed to call critical functions? Is there a pause mechanism for emergencies?
- Reentrancy: Are external calls made before state changes? Are locks used properly?
- Arithmetic: Are all operations using SafeMath or checked arithmetic? Is overflow/underflow prevented?
- Gas optimization: Are loops bounded? Are storage reads minimized? Poor gas use can make contracts unusable.
- Error handling: Does the contract fail gracefully? Does it expose stack traces or internal variables?
- Event logging: Are all state changes logged? Can users and auditors track what happened?
- Upgradeability: Is this contract upgradeable? If so, is the proxy pattern implemented securely?
Infrastructure and Data Security
Code review isn’t just about the contract. It’s about the whole system. Check server configurations. Are RPC endpoints exposed to the public? Is rate limiting in place? Are API keys stored securely? Misconfigured nodes have been exploited to manipulate transaction ordering or inject fake data. Data protection matters too. If your app stores off-chain data (user profiles, transaction metadata), make sure it’s encrypted. Use AES-256 for data in transit and at rest. For databases, enable Transparent Data Encryption (TDE) or Column-Level Encryption (CLE). Never store private keys or seed phrases in logs or config files.Why Formal Verification Is the Future
The most advanced teams are now using formal verification. This isn’t testing. It’s math. Formal verification uses tools like Certora or KeY to prove that a contract behaves correctly under all possible conditions. Instead of running 1,000 test cases, you write mathematical specifications: “If the user has enough balance, they can withdraw.” Then the tool checks if the code satisfies that rule for every input. Nethermind predicts that by 2025, 60% of high-value smart contracts will use formal verification alongside traditional reviews. It’s not for every project-it’s complex and time-consuming-but for DeFi protocols holding billions, it’s becoming standard.What Not to Do
Here are the biggest mistakes teams make:- Using AI tools as final reviewers. LLMs like ChatGPT can explain code, but they can’t detect subtle logic flaws. Sigma Prime warns: “LLMs are great for learning, terrible for auditing.” Always verify their suggestions manually.
- Skipping peer reviews. One person can miss things. Two eyes see more than one. Even senior devs need feedback.
- Waiting until the last minute. Reviews should start early and happen often. Integrate them into your CI/CD pipeline. 63% of teams now run automated scans on every commit.
- Assuming “it works on testnet” means it’s safe. Testnets don’t replicate real-world stress. Attackers don’t play nice. Simulate real attacks during review.
Who Should Do the Review?
Blockchain code review requires specialized skills. You need:- Deep knowledge of the blockchain platform (EVM, Solana, Cosmos, etc.)
- Experience with smart contract languages (Solidity, Rust, Move)
- Understanding of common attack patterns (reentrancy, oracle manipulation, front-running)
- Familiarity with cryptographic primitives (hashing, signatures, Merkle proofs)
Market Trends and Regulation
The demand for blockchain security is exploding. The market was worth $1.14 billion in 2022. By 2032, it’s projected to hit $15.68 billion. Why? Because institutions are moving in. Regulators are catching up. The EU’s MiCA regulation requires crypto service providers to implement standardized code review processes. In the U.S., state and federal agencies are starting to demand audit reports before approving blockchain-based financial products. By 2026, 101Blockchains forecasts that 75% of enterprise blockchain projects will have mandatory code reviews built into their compliance frameworks. This isn’t optional anymore. It’s a legal and financial necessity.Final Advice: Slow Down to Go Fast
The temptation is to ship fast. To cut corners. To say “we’ll fix it later.” Don’t. A week spent on a thorough review saves months of damage control, lawsuits, and reputational ruin. The most successful blockchain projects aren’t the ones that launched first. They’re the ones that launched without a single exploitable bug. Start with a checklist. Use both tools and humans. Review early. Review often. Assume nothing. Question everything. Because in blockchain, the cost of a mistake isn’t a bug report. It’s a bank account emptied.Why can't you patch blockchain code after deployment?
Blockchain code is stored on a distributed ledger, which is immutable by design. Once a smart contract is deployed, its code cannot be changed. Even if you control the contract, the network nodes won’t accept updates. The only way to “fix” it is to deploy a new contract and migrate users-a complex, risky process that doesn’t undo past damage.
Can automated tools fully replace manual code review in blockchain?
No. Automated tools like SonarQube or Slither catch common patterns-like unchecked external calls or reentrancy-but they miss business logic flaws. For example, an automated tool won’t know if a function should only be callable by the owner if the owner is a multisig wallet. Only a human reviewer who understands the project’s intent can spot those errors.
How long should a blockchain code review take?
It depends on complexity. A simple ERC-20 token might take 3-5 days. A DeFi protocol with lending, staking, and oracle integrations can take 2-4 weeks. The key is not speed-it’s thoroughness. Rushing a review is how vulnerabilities slip through.
What’s the difference between a smart contract audit and a code review?
They’re often used interchangeably, but there’s a nuance. A code review is the technical process of examining source code line by line. A smart contract audit is a broader process that includes code review, testing, threat modeling, and sometimes formal verification. An audit report usually includes risk ratings and remediation steps. Code review is one part of an audit.
Is it safe to use AI tools like ChatGPT for blockchain code review?
Only as a learning aid. AI can help explain code or suggest fixes, but it doesn’t understand context, intent, or real-world attack vectors. It can generate convincing but incorrect advice. Sigma Prime and other top security firms explicitly warn against relying on AI for final security assessments. Always verify AI suggestions manually by tracing execution paths and testing edge cases.
What skills do I need to become a blockchain code reviewer?
You need deep knowledge of blockchain architecture (consensus, EVM, gas mechanics), experience writing and reading smart contracts (Solidity, Rust), understanding of common exploits (reentrancy, oracle manipulation, front-running), and familiarity with cryptographic primitives. Most professionals spend 6-12 months focused training before they’re ready to conduct serious reviews. Start by auditing open-source contracts on GitHub, then move to formal training programs from Sigma Prime or Certora.
Derek Hardman
1 11 25 / 22:18 PMBlockchain code review is one of those areas where cutting corners doesn't just risk failure-it invites catastrophe. I've seen teams rush deployments because of investor pressure, only to watch millions vanish in a single transaction. The immutability factor isn't theoretical; it's a legal and financial wall. Once it's live, you're not just fixing code-you're rebuilding trust, often from zero.
What's often overlooked is how much cultural pressure contributes to sloppy reviews. Developers are rewarded for speed, not safety. That needs to flip. Security should be the KPI, not deployment frequency.
Eliane Karp Toledo
3 11 25 / 02:18 AMThey say blockchain is immutable but who really controls the nodes? Governments, central banks, the same people who crashed the economy in 2008. They’re letting us think we’re decentralized while quietly backdooring every major chain. Formal verification? That’s just a fancy way to make the code look clean while they still own the keys.
Phyllis Nordquist
4 11 25 / 07:02 AMThank you for this comprehensive breakdown. The distinction between code review and audit is particularly valuable-I’ve seen too many teams conflate the two, leading to false confidence. The checklist you provided is excellent and should be mandatory reading for any team deploying on-chain. I would only add: always include a threat modeling session before the first review cycle. Identify your highest-value assets and assume they’re already targeted.
Additionally, while formal verification is expensive, its ROI becomes undeniable when you consider the cost of a single exploit. For high-value protocols, it’s not an option-it’s insurance.
Eric Redman
6 11 25 / 03:38 AMLMAO they said 'use SonarQube' like that's gonna catch a reentrancy bug disguised as a 'gas optimization trick'. I've seen devs write 300 lines of convoluted code just to make a tool think it's safe. Automated tools are for people who don't want to read code. Real security is sweat, coffee, and staring at the same 12 lines for 3 hours until your eyes bleed.
Also, AI reviewers? Please. ChatGPT once told me 'require(msg.sender != address(0))' was 'redundant'. Bro, that's how you get a 200M exploit.
Jason Coe
6 11 25 / 04:58 AMMan, I’ve been doing this for seven years now and I still get nervous before every deploy. It’s not just about the code-it’s about the people behind it. Are they tired? Are they being rushed? Are they afraid to say ‘this doesn’t feel right’? The best reviews I’ve done weren’t the ones with the most tools-they were the ones where someone paused and said, ‘Wait, why does this function even exist?’
I’ve seen teams skip peer reviews because ‘everyone’s busy.’ That’s how you get Poly Network. One person missed a single access control check. One. And $600M vanished. No one got fired. No one even apologized. Just another ‘learning experience.’
Don’t treat security like a checkbox. Treat it like a ritual. Light a candle. Say a prayer. Read the code aloud. Make it sacred. Because if you don’t, someone else will make it a funeral.
Also, testnets are lies. Mainnet is the only truth. And mainnet doesn’t care if you’re ‘almost ready.’
TL;DR: Slow down. Breathe. Review like your life depends on it-because someone’s life, or savings, or retirement, might.
Brett Benton
6 11 25 / 21:23 PMYo, if you’re not using formal verification by now, you’re basically leaving your front door open and putting a sign that says ‘FREE MONEY’ in neon lights. I’ve been auditing DeFi projects since 2020 and the ones that survived? They all had Certora or similar running in CI. The rest? Gone. Poof. Like they never existed.
And yeah, AI tools are trash for real audits. I asked GPT-4 to audit a contract once-it said a function was ‘secure’ because it had a ‘require’ statement. Bro, that function was calling an external contract with no checks and no reentrancy guard. It’s like asking a toddler to check your locks.
But here’s the real kicker: the people who need this the most? They’re the ones who think they’re too big to fail. That’s the scariest part.
David Roberts
8 11 25 / 06:09 AMImmutable ledgers? That’s just a semantic veneer. The real immutability is economic. Once a contract is deployed, the economic incentives of the network ensure its persistence. You can’t change the code, but you can change the governance. And governance is always mutable. Always. The DAO hack didn’t fail because of code-it failed because the community lacked the mechanism to override it. That’s the real lesson: code is static, power is fluid.
Formal verification is a mathematical placebo. It proves consistency, not correctness. And correctness is defined by human intent-which can never be formalized. You’re not verifying logic. You’re verifying assumptions. And assumptions are always wrong.
Monty Tran
9 11 25 / 07:31 AMBottom up review is for amateurs. If you don’t start at the entry points you’re already dead. Top down is the only way. You think you’re being thorough checking storage variables? You’re wasting time. Attackers don’t care about your uint256s. They care about who can call functionX. That’s it. Everything else is noise.
Automated tools? Useless. They’re trained on past exploits. The next exploit hasn’t happened yet. Humans see patterns. Machines see syntax.
AI reviewers? Laughable. They hallucinate. They make up functions. They invent security patterns that don’t exist. You trust AI to audit your contract? You deserve to lose everything.
Hanna Kruizinga
10 11 25 / 22:41 PMThey’re all lying. The whole blockchain security industry is a pyramid scheme. Auditors make millions while projects get hacked anyway. Who audits the auditors? No one. Halborn? Sigma Prime? They’re all part of the same club. They get paid to say it’s safe. Then the exploit happens. They tweet ‘we’re investigating.’ Meanwhile, the funds are already in Tornado Cash.
And formal verification? That’s just a buzzword for ‘we’re charging you $500k to say the same thing your 22-year-old dev could’ve caught if he’d slept.’
DeeDee Kallam
11 11 25 / 10:19 AMyou ever just… not deploy? like… what if the best code review is not writing the code at all? i mean… why are we even doing this? the whole system is rigged. blockchain is just a way for rich people to feel smart while stealing from poor people who believe in ‘decentralization’
Bhavna Suri
13 11 25 / 00:22 AMThis is too complicated. Why not just use a simple contract? Why need all these tools? Why need formal verification? Just make it small. Make it clear. Then it will be safe. No need for all this noise.
Elizabeth Melendez
14 11 25 / 15:44 PMI just want to say how much I appreciate this post-it’s the kind of thing I wish I’d had when I started out. I was a junior dev thinking ‘if it compiles, it works.’ Then I saw a friend’s project get drained because of an unchecked external call. I cried. Not for the money-for the trust.
Since then, I’ve made it my mission to review every single line of code I touch. I read it out loud. I draw diagrams. I ask ‘what if?’ a hundred times. I’ve missed sleep. I’ve missed dinners. But I’ve never missed a bug.
And to anyone thinking ‘we don’t have time’-you don’t have time not to. The cost of a mistake isn’t just financial. It’s emotional. It’s the sleepless nights. The guilt. The emails from users asking ‘why did you do this to me?’
You’re not just writing code. You’re holding people’s futures in your hands. Treat it like that.
And yes, AI is garbage for audits. I’ve seen it suggest ‘use assembly to optimize’ and accidentally create a reentrancy. Don’t let it near your contract.
Review early. Review often. And never, ever trust the testnet.
Phil Higgins
16 11 25 / 06:00 AMLet me be blunt: if your team doesn’t have a dedicated blockchain security reviewer, you are not a serious project. You are a gamble. And gambling with other people’s money is not innovation-it’s theft by omission.
There is no shortcut. No magic tool. No AI that understands intent. The only way to build trust is through relentless, meticulous, human-driven review. This is not a phase. It is the foundation.
And to those who say ‘we’re too small’-you’re not. Size doesn’t matter. Impact does. A $10k contract can be exploited to drain $10M if it’s connected to a liquidity pool. Your code doesn’t exist in isolation. It’s part of a web. And every weak link is a door.
Stop optimizing for speed. Start optimizing for survival.
Genevieve Rachal
16 11 25 / 13:07 PMEveryone’s acting like this is some profound revelation. Newsflash: 90% of these ‘best practices’ are just common sense. The fact that we’re even having this conversation is a testament to how badly the industry has failed. You don’t need a 20-page checklist to know you shouldn’t let anyone call a function that transfers funds without authorization.
And formal verification? Please. It’s the blockchain equivalent of using a gold-plated wrench to fix a broken bicycle. Overkill for 99% of projects. And the people who use it? They’re just selling consulting packages.
The real problem? Developers who think they’re engineers but have never read a single whitepaper. They copy-paste OpenZeppelin and call it a day. That’s not security. That’s negligence dressed up as innovation.
Eli PINEDA
18 11 25 / 08:31 AMwait so if i use safe math and check access control and use a pause button… is that enough? or do i need to also check if the owner is a multisig? and what if the oracle is compromised? and what if someone frontruns the pause? i’m so confused now
Debby Ananda
19 11 25 / 16:44 PMFormal verification? 😍 So elegant. So mathematical. So… 💎💎💎 I just want to cry thinking about how beautiful it is when the math proves the code is perfect. Like a ballet of logic. ✨
Also, I’m wearing my Certora hoodie right now. It’s silk. And I bought it in Geneva. 🤍
Vicki Fletcher
21 11 25 / 01:50 AMThank you for this. I’ve been reviewing contracts for three years now, and I still find myself going back to the checklist every single time. Even when I’m tired. Even when the team says ‘we’re on a deadline.’ I pause. I breathe. I go line by line.
One time, I caught a reentrancy that only triggered if a user called a function during a block reorg. The dev said, ‘that’s impossible.’ I simulated it. It happened. They fixed it. Saved $20M.
Don’t let anyone rush you. Don’t let anyone tell you ‘it’s fine.’ If you feel uneasy, you’re right. Trust that feeling.
And please-don’t use AI. Not even as a ‘second opinion.’ It doesn’t understand context. It doesn’t understand fear. It doesn’t understand that someone’s life savings are on the line.
You’re not just writing code. You’re writing the future.
Jason Coe
23 11 25 / 01:22 AMAnd to the person who said ‘just use a simple contract’-you’re right. But most projects aren’t simple. They’re layered. They’re interconnected. They rely on oracles, price feeds, liquidity pools, and other contracts. You can’t just ‘keep it simple’ if you’re building DeFi. The complexity is the point. The challenge is managing it without breaking.
So yes-start simple. But know that ‘simple’ today becomes ‘complex’ tomorrow. And when it does, your review process has to grow with it.
That’s why the checklist isn’t static. It’s alive. It evolves. Like your code.