web3-audit
Lets your agent review smart contract code. It looks for security errors in blockchain systems.
What it does
This tool helps check the security of smart contract code (programs that run on a blockchain). It looks for common flaws that hackers might exploit.
When to use it
- ✓When reviewing new smart contract code.
- ✓When investigating a potential security issue in a contract.
- ✓To learn about common contract vulnerabilities.
Example of what to ask your AI
“Analyze this contract for common security flaws.”
Want more? Open the sections below.
How to use
The easiest way: copy the message below and paste it into Claude, ChatGPT, Cursor or any AI. It reads the skill and follows the instructions.
Skill link
Ready-to-paste message
How it works
The tool examines the code for known vulnerability patterns, like access control issues or inconsistencies in data updates. It compares the code against examples of real-world failures.
Installation
Easiest way: copy the skill link and paste it into Claude, ChatGPT or Cursor asking it to follow the instructions.
In the terminal (Claude Code, Codex, Cursor), in your project folder:
npx skills add sickn33/agentic-awesome-skills --skill web3-auditOr download just the file:
curl -L https://raw.githubusercontent.com/sickn33/agentic-awesome-skills/main/plugins/agentic-awesome-skills-claude/skills/web3-audit/SKILL.md -o SKILL.mdTechnical content (original SKILL.md)
Original text by the author, straight from GitHub.
⚠️ AUTHORIZED USE ONLY This skill is for educational purposes or authorized security assessments only. You must have explicit, written permission from the system owner before using this tool. Misuse of this tool is illegal and strictly prohibited.
Mandatory confirmation gate Before running any command that probes, exploits, changes, persists on, extracts data from, or attempts credential access against a target:
- Ask the user to state the exact target URL, IP, account, or resource.
- Ask the user to confirm written authorization and the permitted scope.
- Show the exact command(s) and explain their expected effect.
- Wait for explicit confirmation in the current conversation.
Without that confirmation, remain read-only and provide defensive guidance only. Prefer a sandbox, disposable VM, or controlled lab.
WEB3 SMART CONTRACT AUDIT
10 bug classes. Pre-dive kill signals. Foundry PoC template. Real paid examples.
PRE-DIVE KILL SIGNALS (check BEFORE any code review)
ZKsync lesson: $322M TVL + OZ audit + 750K LOC + 5 sessions = 0 findings. Large well-audited bridges are extremely hard.
- TVL < $500K → max payout capped too low for effort
- 2+ top-tier audits (Halborn, ToB, Cyfrin, OpenZeppelin) on simple protocol → bugs already found
- Protocol < 500 lines, single A→B→C flow → minimal attack surface
- Formula:
max_realistic_payout = min(10% × TVL, program_cap)— if < $10K, skip
Soft kill: OZ/ToB/Cyfrin audit on current version + codebase > 500K LOC → expect 40+ hours for maybe 1 finding. Only proceed if bounty floor > $50K AND you have protocol-specific expertise.
Target scoring (go if >= 6/10):
- TVL > $10M: +2
- Immunefi program with Critical >= $50K: +2
- No top-tier audit on current version: +2
- < 30 days since deploy: +1
- Protocol you've hunted before: +1
- Source code + natspec comments: +1
- Upgradeable proxies: +1
THE ONE RULE
"Read ALL sibling functions. If
vote()has a modifier, checkpoke(),reset(),harvest(). The missing modifier on the sibling IS the bug."
This single rule explains 19% of all Critical findings.
1. ACCOUNTING STATE DESYNCHRONIZATION
#1 Critical bug class — 28% of all Criticals on Immunefi.
What It Is
Two state variables supposed to stay in sync. One code path updates A but forgets B. Later code reads both and makes decisions based on stale B.
Real Value = A - B
If A updated but B isn't → Real Value appears larger → phantom value
Root Cause Patterns
Variant 1: Phantom Yield (Yeet protocol — 35 duplicate reports)
function startUnstake(uint256 amount) external {
totalSupply -= amount; // decremented BEFORE transfer
// aToken.balanceOf(this) still reflects old value
// yieldAmount = aToken.balanceOf - totalSupply = phantom yield
}
Variant 2: Fast Path Skips State Update (Alchemix V3)
function claimRedemption(uint256 tokenId) external {
if (transmuter.balance >= amount) {
transmuter.transfer(user, amount);
_burn(tokenId);
return; // EARLY RETURN — cumulativeEarmarked, _redemptionWeight, totalDebt never updated
}
// Slow path: updates all state vars correctly
alchemist.redeem(...);
}
Variant 3: Update Happens in Wrong Order (Alchemix)
function deposit(uint256 amount) external {
_shares = (amount * totalShares) / totalAssets; // calculated BEFORE deposit
totalAssets += amount; // assets added AFTER shares calculated → wrong rate
}
Grep Patterns
# Find all accounting variables
grep -rn "totalSupply\|totalShares\|totalAssets\|totalDebt\|cumulativeReward\|rewardPerShare" contracts/
# Find all early returns in claim/redeem functions
grep -rn "\breturn\b" contracts/ -B3 | grep -B3 "if\b"
# For each early return: which state updates in normal path are skipped?
2. ACCESS CONTROL
#2 Critical — 19% of Criticals. $953M lost in 2024 alone.
Variant 1: Missing Modifier on Sibling Function
function vote(uint256 tokenId) external onlyNewEpoch(tokenId) { // guarded
function reset(uint256 tokenId) external onlyNewEpoch(tokenId) { // guarded
function poke(uint256 tokenId) external { // NO GUARD → infinite FLUX inflation
}
Variant 2: Wrong Check (Existence vs Ownership)
function split(uint256 tokenId, uint256 amount) external {
…
FAQ
What is a smart contract?
It's a computer program that runs on a blockchain. It automatically executes actions when certain conditions are met, without needing intermediaries.
What is a blockchain?
It's a digital, decentralized, and distributed ledger that records transactions securely and transparently.
Why is smart contract security important?
Smart contracts handle value (money, digital assets). Security flaws can lead to the loss of these assets.
Details
Popularity
- GitHub stars
- 48k
- Ranking position
- #4546
- License
- MIT
- Updated
- 10/15/2026
Comments
- …
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