fuzzer

fuzzer is a skill for Claude Code from ZealynxSecurity/krait. It costs 0 tokens per session (1,554 once invoked), scanned A, original, MIT.

A method for turning smart-contract rules into Foundry fuzz tests. Fuzz testing runs tests with many varied input values to check that important properties always remain true.

In plain words
What is it for?
Use it to document contract invariants, generate tests for them, and investigate whether test failures reveal a broken rule or a faulty test.
Why use it?
It checks whether accounting, permissions, state changes, token balances, and other rules hold across many inputs instead of only a few examples.

Skill for Claude Code

Written for Claude Code: installed under .claude/.

Needs its repository: it reads a path above its own folder, which exists only inside the repository. The line is import {Vault} from "../src/Vault.sol";.

Good fit Use it to document contract invariants, generate tests for them, and investigate whether test failures reveal a broken rule or a faulty test.

Compare 6 skills from other repositories ↓
Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo
git clone --depth 1 https://github.com/ZealynxSecurity/krait
agentmods
npx agentmods add skills/zealynxsecurity/krait/fuzzer

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for fuzzer

README.md
[![agentmods](https://agentmods.dev/badge/skills/zealynxsecurity/krait/fuzzer/github.svg)](https://agentmods.dev/skills/zealynxsecurity/krait/fuzzer)
Your own site
<a href="https://agentmods.dev/skills/zealynxsecurity/krait/fuzzer"><img src="https://agentmods.dev/badge/skills/zealynxsecurity/krait/fuzzer/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for fuzzer

Your own site · 80×15
<a href="https://agentmods.dev/skills/zealynxsecurity/krait/fuzzer"><img src="https://agentmods.dev/badge/skills/zealynxsecurity/krait/fuzzer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,554 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00000 $0.01554
Opus 5.5 $0.00000 $0.00622
Sonnet 5.5 $0.00000 $0.00311
Haiku 4.5 $0.00000 $0.00155

Measured 1mo ago against content hash 95c3685662c3, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

fuzzer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/krait/fuzzer/SKILL.md · 222 lines

How it starts

The opening of the file, as written. The whole thing — 222 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Krait Fuzzer — Invariant Extraction & Testing Methodology

This skill defines how to extract invariants from smart contracts and generate Foundry fuzz tests to verify them.

Core Principle

The LLM does NOT audit for vulnerabilities. It:

  1. Understands the code deeply
  2. Documents all invariants (properties that must always hold)
  3. Generates Foundry tests to verify those invariants
  4. Iterates on test failures to distinguish test bugs from real violations

Invariant Categories

Category Description Example
accounting Balance/supply consistency totalSupply == sum(balances[i])
access-control Permission boundaries onlyOwner can call pause()
state-transition Valid state machine flows state can only go ACTIVE → PAUSED → ACTIVE
economic Price/rate/value bounds exchangeRate >= 1e18 (never decreases)
token-conservation No token creation/destruction tokensBefore + deposited == tokensAfter
ordering Temporal constraints withdrawTime > depositTime
bounds Value range constraints fee <= MAX_FEE
relationship Multi-variable relationships debt <= collateral * ltv / 1e18

Invariant Extraction Methodology

Step 1: State Variable Analysis

For each contract:

  1. List ALL storage variables
  2. Group related variables (e.g., totalSupply and balances mapping)
  3. Identify computed relationships: does variable A depend on variable B?
  4. Check constructor/initializer: what invariants are established at deployment?

Step 2: Require/Assert Mining

Every require() and assert() is a developer-stated invariant:

require(balances[msg.sender] >= amount, "insufficient");  // INV: balance >= withdrawal
assert(totalSupply == _computeTotal());                     // INV: supply consistency

Also check modifiers — onlyOwner, whenNotPaused, nonReentrant all encode invariants.

Step 3: Function-Level Invariants

Read the full file on GitHub · 222 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 1mo ago First seen · 222 lines · 0 tokens per session scan A 95c3685662c3

Subscribe to this mod's changes

fuzzer is a skill published in the GitHub repository ZealynxSecurity/krait (25 stars, last pushed 22d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 1,554 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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