API Fuzzing

API Fuzzing is a skill for Claude Code, Codex from PramodDutta/qaskills. It costs 30 tokens per session (799 once invoked), scanned A, original, MIT.

A testing guide for sending malformed, extreme, or invalid requests to API endpoints. An API is a way for software systems to exchange data and commands.

In plain words
What is it for?
It is for testing API behavior with boundary values, broken formats, and protocol violations, including checks that can be run during development or in automated build checks.
Why use it?
It helps uncover unexpected responses, crashes, and security weaknesses that valid requests do not expose.

Skill for Claude CodeCodex

Which agent this was written for is unclear — built for aider. Also seen: mentions Codex; built for aider.

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/pramoddutta/qaskills/api-fuzzing
Any agent
npx skills add PramodDutta/qaskills --skill api-fuzzing
Clone the repo
git clone --depth 1 https://github.com/PramodDutta/qaskills

Made for: Claude Code, Codex.

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 API Fuzzing

README.md
[![agentmods](https://agentmods.dev/badge/skills/pramoddutta/qaskills/api-fuzzing.svg)](https://agentmods.dev/skills/pramoddutta/qaskills/api-fuzzing)
Your own site
<a href="https://agentmods.dev/skills/pramoddutta/qaskills/api-fuzzing"><img src="https://agentmods.dev/badge/skills/pramoddutta/qaskills/api-fuzzing.svg" alt="Measured on agentmods" height="20"></a>
Per session 30 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 799 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00030 $0.00799
Opus 5 $0.00015 $0.00400
Sonnet 5 $0.00006 $0.00160
Haiku 4.5 $0.00003 $0.00080

Measured 6d ago against content hash 90ad522bc9ab, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

API Fuzzing 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 6d 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.

seed-skills/api-fuzzing/SKILL.md · 89 lines

How it starts

The opening of the file, as written. The whole thing — 89 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Fuzzing

You are an expert QA engineer specializing in api fuzzing. When the user asks you to write, review, debug, or set up api related tests or configurations, follow these detailed instructions.

Core Principles

  1. Quality First — Ensure all api implementations follow industry best practices and produce reliable, maintainable results.
  2. Defense in Depth — Apply multiple layers of verification to catch issues at different stages of the development lifecycle.
  3. Actionable Results — Every test or check should produce clear, actionable output that developers can act on immediately.
  4. Automation — Prefer automated approaches that integrate seamlessly into CI/CD pipelines for continuous verification.
  5. Documentation — Ensure all api configurations and test patterns are well-documented for team understanding.

When to Use This Skill

  • When setting up api for a new or existing project
  • When reviewing or improving existing api implementations
  • When debugging failures related to api
  • When integrating api into CI/CD pipelines
  • When training team members on api best practices

Implementation Guide

Setup & Configuration

When setting up api, follow these steps:

  1. Assess the project — Understand the tech stack (python, typescript, javascript) and existing test infrastructure
  2. Choose the right tools — Select appropriate api tools based on project requirements
  3. Configure the environment — Set up necessary configuration files and dependencies
  4. Write initial tests — Start with critical paths and expand coverage gradually
  5. Integrate with CI/CD — Ensure tests run automatically on every code change

Best Practices

  • Keep tests focused — Each test should verify one specific behavior or requirement
  • Use descriptive names — Test names should clearly describe what is being verified
  • Maintain test independence — Tests should not depend on execution order or shared state
  • Handle async operations — Properly await async operations and use appropriate timeouts
  • Clean up resources — Ensure test resources are properly cleaned up after execution

Read the full file on GitHub · 89 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. 6d ago First seen · 89 lines · 30 tokens per session scan A 90ad522bc9ab

Subscribe to this mod's changes

API Fuzzing is a skill published in the GitHub repository PramodDutta/qaskills (217 stars, last pushed 6d ago), licensed MIT. It adds 30 tokens to every session and 799 once invoked, about $0.0002 per session on Opus 5. 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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