testing-apis

A checklist and testing guide for finding security flaws in REST and GraphQL APIs. APIs are interfaces that let software exchange data and actions over a network.

In plain words
What is it for?
Use it when penetration-testing APIs or microservices, including endpoint discovery, API fuzzing, business-logic checks, authentication and authorization testing, and GraphQL testing.
Why use it?
An API may expose data or actions to the wrong person even when the main application looks secure. Testing can reveal authentication bypasses, access-control mistakes, injection, unsafe field updates, and missing rate limits.

Skill for Claude CodeCodex

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/evilfreelancer/secs/testing-apis
Any agent
npx skills add EvilFreelancer/secs --skill testing-apis
Clone the repo
git clone --depth 1 https://github.com/EvilFreelancer/secs

Made for: Claude Code, Codex.

Per session 43 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,399 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 2 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 $0.00043 $0.03399
Opus 5 $0.00022 $0.01699
Sonnet 5 $0.00009 $0.00680
Haiku 4.5 $0.00004 $0.00340

Measured 2d ago against content hash 113b24d7c0e0, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

testing-apis scanned grade A with 2 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 2d 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.

Sends data to an external URLlowData exfiltration

A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.

TOKEN_A=$(curl -X POST https://api.target.com/login -d '{"username":"userA","password":"passA"}' | jq -r .token)

Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl https://target.com/swagger.json
.agents/skills/testing-apis/SKILL.md · 478 lines

How it starts

The opening of the file, as written. The whole thing — 478 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Security Testing Skill

You are an API security expert specializing in REST, GraphQL, and API pentesting. Use this skill when the user requests help with:

  • REST API security testing
  • GraphQL API exploitation
  • API authentication bypass
  • API authorization flaws
  • Rate limiting bypass
  • API fuzzing
  • Mass assignment vulnerabilities
  • API documentation discovery

When to Use

Activate this skill when the user asks to:

  • Test REST or GraphQL APIs
  • Find API vulnerabilities
  • Bypass API authentication/authorization
  • Discover API endpoints
  • Test API business logic
  • Perform API fuzzing
  • Analyze API documentation
  • Help with API penetration testing

When NOT to Use

  • Source code is available — use auditing-code-for-vulnerabilities
  • Browser-rendered application surface — use testing-web-applications
  • Token and signature construction review — use reviewing-cryptography
  • LLM/agent tool APIs — use securing-ai-systems
  • A parameter that makes the server fetch a URL — use testing-web-applications
  • A body or cookie holding a serialized object — use testing-web-applications
  • An XML or SOAP body that may resolve external entities — use testing-web-applications

Core Methodologies

1. API Discovery and Reconnaissance

Find API Endpoints:

# Common API paths
/api/
/api/v1/
/api/v2/
/rest/
/graphql
/swagger
/api-docs
/swagger.json
/swagger.yaml
/openapi.json
/api/swagger-ui/
/api/docs

# Directory fuzzing for APIs
ffuf -u https://target.com/FUZZ -w api-wordlist.txt -mc 200,301,302,403
gobuster dir -u https://target.com -w api-paths.txt

# JavaScript analysis
# Extract API endpoints from JS files
cat app.js | grep -Eo "(GET|POST|PUT|DELETE|PATCH)\s+['\"]([^'\"]+)"

API Documentation:

# Swagger/OpenAPI
curl https://target.com/swagger.json
curl https://target.com/v2/swagger.json
curl https://target.com/api-docs

# Check for exposed docs
https://target.com/docs
https://target.com/api/docs
https://target.com/swagger-ui/
https://target.com/redoc

Read the full file on GitHub · 478 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 2d ago First seen · 478 lines · 43 tokens per session scan A 113b24d7c0e0

Subscribe to this mod's changes

testing-apis is a skill published in the GitHub repository EvilFreelancer/secs (10 stars, last pushed 24d ago), licensed Apache-2.0. It adds 43 tokens to every session and 3,399 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 2 findings (sends data to an external url, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Related

Other skills, from other repositories

Blue Team Defense & Hardening

System hardening, detection engineering, security baseline monitoring, patch management, defense-in-depth architecture, and security posture improvement.

Masriyan/Claude-Code-CyberSecurity-Skill · 30 tokens

analyzing-email-headers-for-phishing-investigation

Parse and analyze email headers to trace the origin of phishing emails, verify sender authenticity, and identify spoofing through SPF, DKIM, and DMARC validation.

26zl/cybersec-toolkit · 44 tokens

analyzing-golang-malware-with-ghidra

Reverse engineer Go-compiled malware using Ghidra with specialized scripts for function recovery, string extraction, and type reconstruction in stripped Go binaries.

26zl/cybersec-toolkit · 40 tokens

analyzing-prefetch-files-for-execution-history

Parse Windows Prefetch files to determine program execution history including run counts, timestamps, and referenced files for forensic investigation.

26zl/cybersec-toolkit · 34 tokens

analyzing-ios-app-security-with-objection

Performs runtime mobile security exploration of iOS applications using Objection, a Frida-powered toolkit that enables security testers to interact with app internals without jailbreaking. Use when assessing iOS app security posture, bypassing client-side protections, dumping keychain items, inspecting filesystem…

26zl/cybersec-toolkit · 99 tokens

add-tool

Use when adding a new cybersecurity tool to this installer. Walks through editing the right module file, adding to toolsconfig.json, running validators, and syncing MCP server data if needed. Triggers on phrases like "add tool", "add ", "register a new tool", "include X in the installer".

26zl/cybersec-toolkit · 68 tokens