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Agent skill

Audit API Contract Implementation

by cyberful in cyberful/cyberful

Audit whether API handlers, gateways, serializers, validators, and generated clients implement the effective contract and its security invariants.

AGPL-3.0Auto-check passedBackend & APIs

Install Audit API Contract Implementation

skills CLI
$ npx skills add cyberful/cyberful --skill audit-api-contract-implementation -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install cyberful/cyberful audit-api-contract-implementation --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/cyberful/cyberful.git skills-src && mkdir -p .claude/skills && cp -r skills-src/cyberful/builtin/skills/audit-api-contract-implementation .claude/skills/audit-api-contract-implementation && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
audit-api-contract-implementation
GitHub stars
134
Token cost
~666 tokens
SKILL.md length
227 words
Files
3 (incl. references)
Skills in repo
85
Repo updated
First seen
Licence
AGPL-3.0

At a glance

Audit whether API handlers, gateways, serializers, validators, and generated clients implement the effective contract and its security invariants.

  • Code-level REST
  • SKILL.md covers Establish the contract set, Trace security invariants and Report evidence-backed drift
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
  • Schema-enforcement

What it does

Audit API Contract Implementation is an agent skill from cyberful/cyberful. Audit whether API handlers, gateways, serializers, validators, and generated clients implement the effective contract and its security invariants. Use for code-level REST, RPC, OpenAPI, schema-enforcement, versioning, and undocumented-route reviews.

Its SKILL.md is about 670 tokens, which your agent loads only when the skill is triggered. The skill folder holds 4 other files, including reference files (for example `agents/openai.yaml` and `references/contract-implementation-review.md`).

It sits in Backend & APIs, covering API design and OpenAPI specifications. It works with OpenAPI. The repository describes itself as: Cyberful is an open-source AI Red Team for discovering, exploiting, verifying, and remediating vulnerabilities. The licence is AGPL-3.0.

When your agent uses it

  • Code-level REST
  • Schema-enforcement
  • Undocumented-route reviews

Example prompts

  • “/audit-api-contract-implementation”

What it can do on your machine

Read from SKILL.md and the folder at commit ec598a6. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md.

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Audit API Contract Implementation loads about 666 tokens when it runs, and up to ~1.2k if it reads all its reference files. Until then it costs about 71 tokens; SKILL.md has 227 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~71
When it runs · the whole SKILL.md, loaded when a task matches
~666
With references · SKILL.md plus every file in references/, read only if the agent opens them
~1.2k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from cyberful/cyberful at commit ec598a6, republished under its AGPL-3.0 licence (© cyberful). 227 words, ~666 tokens.

Download SKILL.mdSave it as .claude/skills/audit-api-contract-implementation/SKILL.md (or your agent's skills folder). This skill also uses 2 other files; get the full folder from GitHub.
name
audit-api-contract-implementation
description
Audit whether API handlers, gateways, serializers, validators, and generated clients implement the effective contract and its security invariants. Use for code-level REST, RPC, OpenAPI, schema-enforcement, versioning, and undocumented-route reviews.
metadata.domain
application-security
metadata.subdomain
api-contract-assurance
metadata.triggers
audit API contract implementation, compare OpenAPI to handlers, find undocumented API routes, review request response schema enforcement, audit generated API…
metadata.tags
API, OpenAPI, schema-validation, route-registration, code-audit

Audit API Contract Implementation

Treat the deployed route table and executable validators as the effective implementation. Treat OpenAPI, protobuf, WSDL, generated clients, examples, and gateway configuration as independent claims to reconcile, not as proof of runtime behavior.

Establish the contract set

Identify contract versions, route registration, middleware order, serializer settings, compatibility adapters, gateway rewrites, and generated artifacts. Record which artifact owns each operation and whether production can expose routes outside it.

Read contract-implementation-review.md when tracing handler registration, validation, and drift. Use analyze-api-contract-coverage when OpenAPI JSON and implementation inventories need a deterministic coverage ledger. Route gRPC or SOAP protocol behavior to their dedicated skills.

Trace security invariants

For each representative operation, follow path, query, headers, metadata, body, identity, tenant, authorization, validation, coercion, side effect, error mapping, and response serialization. Verify that contract-required security is enforced by executable code and that optional, nullable, defaulted, polymorphic, unknown, and duplicate fields cannot change the security decision.

Compare every alternate entrypoint: version aliases, batch routes, internal adapters, async consumers, generated server stubs, direct service calls, and gateway bypasses. Check that deprecation does not leave weaker validators or authorization.

Report evidence-backed drift

Classify each discrepancy as undocumented implementation, unimplemented contract, validation mismatch, security-declaration mismatch, compatibility divergence, or evidence gap. A mismatch becomes a vulnerability only when it violates a security requirement; cite the exact contract location and executable path that establish the difference.

© cyberful, AGPL-3.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 2 other files (references) in cyberful/builtin/skills/audit-api-contract-implementation of cyberful/cyberful.

  • SKILL.md
  • agents/openai.yaml
  • references/contract-implementation-review.md

Open the folder on GitHubat commit ec598a6

Compare with similar skills

Audit API Contract Implementation next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Audit API Contract Implementation compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Audit API Contract Implementation this skillcyberful/cyberful134—~666Automated safety check: PassAGPL-3.0
API DesignerJeffallan/claude-skills12k2 repos~2kAutomated safety check: PassMIT
Old Coder API DesignAmazingAng/old-coder7491 repos~3.4kAutomated safety check: PassMIT
API Surface Reviewpolarsource/polar10k—~1.3kAutomated safety check: PassMIT
API ContractChenyCHENYU/Robot_Admin1k—~1.9kAutomated safety check: PassMIT
API Designyonatangross/orchestkit288—~2.9kAutomated safety check: PassMIT

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Works with

Categories

Questions about Audit API Contract Implementation

What does Audit API Contract Implementation do?

Audit whether API handlers, gateways, serializers, validators, and generated clients implement the effective contract and its security invariants. Audit API Contract Implementation is an agent skill from cyberful/cyberful. Audit whether API handlers, gateways, serializers, validators, and generated clients implement the effective contract and its security invariants.

When should I use Audit API Contract Implementation?

Audit API Contract Implementation fits situations like: code-level REST; schema-enforcement; undocumented-route reviews.

How do I install Audit API Contract Implementation in Claude Code?

Run `npx skills add cyberful/cyberful --skill audit-api-contract-implementation -a claude-code`. Or copy the skill folder (cyberful/builtin/skills/audit-api-contract-implementation in cyberful/cyberful) into .claude/skills/audit-api-contract-implementation in your project. Claude Code loads it when a task matches its description.

How do I install Audit API Contract Implementation in Codex?

Run `npx skills add cyberful/cyberful --skill audit-api-contract-implementation -a codex`. Or copy the skill folder (cyberful/builtin/skills/audit-api-contract-implementation in cyberful/cyberful) into .agents/skills/audit-api-contract-implementation in your project. Codex loads it when a task matches its description.

Can I use Audit API Contract Implementation in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add cyberful/cyberful --skill audit-api-contract-implementation -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/audit-api-contract-implementation, .gemini/skills/audit-api-contract-implementation, .github/skills/audit-api-contract-implementation and .opencode/skills/audit-api-contract-implementation in your project.

What does Audit API Contract Implementation need to run?

SKILL.md names no scripts, command-line tools or credentials: Audit API Contract Implementation is instructions for the agent only.

Does Audit API Contract Implementation access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Audit API Contract Implementation safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Audit API Contract Implementation use?

Audit API Contract Implementation is published under the AGPL-3.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Audit API Contract Implementation use?

About 666 tokens (SKILL.md is roughly 2.7k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 525 tokens, read only when the agent opens those files.

What are the alternatives to Audit API Contract Implementation?

Skills that share tags, products or a category with Audit API Contract Implementation: API Designer (Jeffallan/claude-skills, 12k stars), Old Coder API Design (AmazingAng/old-coder, 749 stars), API Surface Review (polarsource/polar, 10k stars) and API Contract (ChenyCHENYU/Robot_Admin, 1k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Audit API Contract Implementation?

cyberful (a GitHub organization) maintains it in cyberful/cyberful, which has 134 GitHub stars. The repository holds 85 skills in this directory. The repository was last updated on August 24, 2026.

Source: cyberful/cyberful on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.