API Security Testing

A guide for checking APIs for security problems based on the OWASP API Security Top 10, a list of common API risks. It covers login and permissions, unsafe input, access to other users' objects, rate limits, and automated scanning.

In plain words
What is it for?
Use it to create or review API security tests, check authentication before permissions, test every input location, and set up scans with ZAP and custom scripts.
Why use it?
It helps find cases where an API accepts malicious input, exposes data, grants too much access, or can be exhausted by too many requests.

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

Made for: Claude Code, Codex.

Per session 46 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,961 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. 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 $0.00046 $0.04961
Opus 5 $0.00023 $0.02481
Sonnet 5 $0.00009 $0.00992
Haiku 4.5 $0.00005 $0.00496

Measured 3d ago against content hash bc9184e53801, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

API Security Testing scanned grade A with 1 finding 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 3d 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.

Makes network callslowCapability

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

const response = await fetch(BASE_URL, {
seed-skills/api-security-testing/SKILL.md · 569 lines

How it starts

The opening of the file, as written. The whole thing — 569 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Security Testing Skill

You are an expert in API security testing. When the user asks you to test API security, implement OWASP API Top 10 checks, detect authentication and authorization vulnerabilities, or set up automated security scanning, follow these detailed instructions.

Core Principles

  1. OWASP API Security Top 10 coverage -- Every API security test suite must cover all 10 categories from the OWASP API Security Top 10 list, adapted to the specific API being tested.
  2. Authentication before authorization -- Test authentication mechanisms first (token validation, session management, credential handling), then test authorization (access control, privilege escalation).
  3. Broken Object Level Authorization (BOLA) -- The most critical API vulnerability. Test that every endpoint verifies the requesting user has access to the specific resource being requested.
  4. Input validation at every boundary -- Test all input vectors: path parameters, query strings, headers, request bodies, and file uploads for injection, overflow, and type confusion attacks.
  5. Rate limiting and resource exhaustion -- Verify that APIs implement rate limiting, request size limits, and pagination caps to prevent denial-of-service attacks.
  6. Sensitive data exposure -- Verify that APIs do not leak sensitive information in responses, error messages, headers, or logs.
  7. Automated scanning plus manual testing -- Automated tools catch common vulnerabilities. Manual testing catches business logic flaws. Both are required.

Project Structure

security-tests/
  owasp/
    bola.test.ts
    broken-auth.test.ts
    broken-object-property.test.ts
    unrestricted-resource.test.ts
    broken-function-level-auth.test.ts
    mass-assignment.test.ts
    ssrf.test.ts
    security-misconfiguration.test.ts
    improper-inventory.test.ts
    unsafe-api-consumption.test.ts
  auth/
    token-validation.test.ts
    session-management.test.ts
    credential-handling.test.ts
    oauth-flow.test.ts
  injection/
    sql-injection.test.ts
    nosql-injection.test.ts
    command-injection.test.ts
    xss-injection.test.ts
    header-injection.test.ts
  rate-limiting/
    rate-limit.test.ts
    resource-exhaustion.test.ts
  helpers/
    api-client.ts
    token-generator.ts
    payload-generator.ts
    vulnerability-reporter.ts
  config/
    security-config.ts
    endpoints.ts
  reports/
    .gitkeep

Read the full file on GitHub · 569 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. 3d ago First seen · 569 lines · 46 tokens per session scan A bc9184e53801

Subscribe to this mod's changes

API Security Testing is a skill published in the GitHub repository PramodDutta/qaskills (214 stars, last pushed 3d ago), licensed MIT. It adds 46 tokens to every session and 4,961 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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