What is api-security?

A security testing guide for application programming interfaces, the endpoints that let software exchange data and actions.

It is for testing REST, GraphQL, gRPC, and WebSocket APIs, OpenAPI or Swagger specifications, JWT and OAuth authentication, endpoint fuzzing, and rate limits.

It helps uncover broken authorization, unsafe authentication, excessive data access, and resource-abuse problems across common API styles.

api-security — Skill for Claude Code and Codex by JustineDevs

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.

Any agent

npx skills add JustineDevs/premortem --skill api-security

Clone the repo

git clone --depth 1 https://github.com/JustineDevs/premortem

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/justinedevs/premortem/api-security/github.svg)](https://agentmods.dev/skills/justinedevs/premortem/api-security)

Your own site

<a href="https://agentmods.dev/skills/justinedevs/premortem/api-security"><img src="https://agentmods.dev/badge/skills/justinedevs/premortem/api-security/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/justinedevs/premortem/api-security"><img src="https://agentmods.dev/badge/skills/justinedevs/premortem/api-security.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 87 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,010 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.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00087	$0.02010
Opus 5	$0.00044	$0.01005
Sonnet 5	$0.00017	$0.00402
Haiku 4.5	$0.00009	$0.00201

Measured 9d ago against content hash 0fa0f65444fc, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

api-security 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 9d 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.

.agents/skills/security/api-security/SKILL.md · 179 lines

How it starts

The opening of the file, as written. The whole thing — 179 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Security Testing

Thin router for API penetration testing. Use the index sections to load the specific workflow, payload file, or methodology doc for the phase you're in. Do not pre-load everything.

When to Use

Pentesting a REST, GraphQL, gRPC, or WebSocket API.
OWASP API Top 10 (2023) coverage assessment.
BOLA / BFLA / BOPLA authorization matrix analysis.
JWT / OAuth / API-key auth testing.
Fuzzing endpoints, parameters, or schemas.
Parsing and attacking OpenAPI / Swagger / GraphQL schemas.
Rate-limit / resource-consumption testing.

Trigger Phrases

"pentest this API", "test the REST API", "test GraphQL security", "check for BOLA/IDOR", "analyze OpenAPI spec", "test API authentication", "JWT attacks", "fuzz API endpoints", "GraphQL introspection".

When NOT to Use This Skill

Browser / DOM-based testing (XSS, CSP, clickjacking, client-side auth flows rendered in a browser) -> use dast-automation.
Reviewing API source code for injection/authz bugs at the code level -> use sast-orchestration.
Mobile client reversing to recover API endpoints from an APK/IPA -> use mobile-security first, then return here with the recovered spec.
Cloud-provider IAM / API-gateway config auditing (not the API itself) -> use cloud-security.

Decision Tree

Is there a schema (OpenAPI / GraphQL SDL / .proto)?
  yes -> parse it first, feed endpoints.txt to fuzzers
  no  -> methodology/api_recon.md

What protocol?
  REST / JSON over HTTP -> workflows/rest_testing.md
  GraphQL               -> workflows/graphql_introspection_triage.md
                           then workflows/graphql_testing.md
  gRPC                  -> workflows/grpc_testing.md
  WebSocket             -> workflows/websocket_testing.md

Is a JWT in use?
  yes -> workflows/jwt_attack_chooser.md  (alg-none -> key-conf -> kid -> brute)

Primary finding target?
  Authorization bugs  -> methodology/bola_bfla_matrix.md  (HIGHEST yield)
  Misconfig / inventory -> nuclei + references/owasp_api_top10_2023.md (API8/API9)
  Injection / SSRF    -> payloads/injection.txt

Read the full file on GitHub · 179 lines

Files

What ships with it

21 files 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.

9d ago First seen · 179 lines · 87 tokens per session scan A 0fa0f65444fc

Subscribe to this mod's changes

api-security is a skill published in the GitHub repository JustineDevs/premortem (2 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 87 tokens to every session and 2,010 once invoked, about $0.0004 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 2026-09-03.

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