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Agent skill

OpenAPI Spec Generation

by wshobson in wshobson/agents

Create, validate and maintain OpenAPI 3.1 specs for REST APIs, whether designed first or generated from existing code, and use them for docs and client SDKs.

MITAuto-check passedBackend & APIs

Install OpenAPI Spec Generation

skills CLI
$ npx skills add wshobson/agents --skill openapi-spec-generation -a claude-code

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

GitHub CLI
$ gh skill install wshobson/agents openapi-spec-generation --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/wshobson/agents.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/documentation-generation/skills/openapi-spec-generation .claude/skills/openapi-spec-generation && 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
openapi-spec-generation
GitHub stars
40k
Used in
9 other repos
Token cost
~511 tokens
SKILL.md length
177 words
Files
3 (incl. references)
Skills in repo
142
Repo updated
First seen
Licence
MIT

At a glance

Create, validate and maintain OpenAPI 3.1 specs for REST APIs, whether designed first or generated from existing code, and use them for docs and client SDKs.

  • Works in 2 steps: OpenAPI 3.1 Structure → Design Approaches
  • Writing an API contract before implementation starts
  • SKILL.md covers When to Use This Skill, Core Concepts, Templates and detailed worked… and Best Practices
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

This skill covers writing OpenAPI 3.1 specifications for RESTful APIs and keeping them accurate. It compares three approaches: design-first, where the spec is written before the code; code-first, where the spec is generated from an existing API; and a hybrid in which annotated code produces the spec.

Style rules include reusing schemas with $ref, adding realistic examples, documenting every error code, defining all security schemes, being explicit about nullable fields, using server variables instead of hardcoded URLs and versioning the spec semantically. Outputs feed documentation portals and client SDK generation. A code-first and tooling reference plus a details file hold the longer examples.

When your agent uses it

  • Writing an API contract before implementation starts
  • Generating an OpenAPI spec from an existing REST service
  • Checking that an API implementation matches its spec
  • Producing client SDKs or a docs portal from a spec

Example prompts

  • “Write an OpenAPI 3.1 spec for a bookstore API with books, authors and orders.”
  • “Generate a spec from the routes in src/api and flag undocumented error responses.”
  • “Check whether our users endpoints still match openapi.yaml.”

Workflow steps

2 steps, taken from the step headings in SKILL.md.

  1. OpenAPI 3.1 Structure
  2. Design Approaches

What it can do on your machine

Read from SKILL.md and the folder at commit 46891e7. 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 (its code samples are yaml).

    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

OpenAPI Spec Generation loads about 511 tokens when it runs, and up to ~6.4k if it reads all its reference files. Until then it costs about 55 tokens; SKILL.md has 177 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~55
When it runs · the whole SKILL.md, loaded when a task matches
~511
With references · SKILL.md plus every file in references/, read only if the agent opens them
~6.4k

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 wshobson/agents at commit 46891e7, republished under its MIT licence (© wshobson). 177 words, ~511 tokens.

Download SKILL.mdSave it as .claude/skills/openapi-spec-generation/SKILL.md (or your agent's skills folder). This skill also uses 2 other files; get the full folder from GitHub.
name
openapi-spec-generation
description
Generate and maintain OpenAPI 3.1 specifications from code, design-first specs, and validation patterns. Use when creating API documentation, generating SDKs, or ensuring API contract compliance.

OpenAPI Spec Generation

Comprehensive patterns for creating, maintaining, and validating OpenAPI 3.1 specifications for RESTful APIs.

When to Use This Skill

  • Creating API documentation from scratch
  • Generating OpenAPI specs from existing code
  • Designing API contracts (design-first approach)
  • Validating API implementations against specs
  • Generating client SDKs from specs
  • Setting up API documentation portals

Core Concepts

1. OpenAPI 3.1 Structure
yaml
openapi: 3.1.0
info:
  title: API Title
  version: 1.0.0
servers:
  - url: https://api.example.com/v1
paths:
  /resources:
    get: ...
components:
  schemas: ...
  securitySchemes: ...
2. Design Approaches
ApproachDescriptionBest For
Design-FirstWrite spec before codeNew APIs, contracts
Code-FirstGenerate spec from codeExisting APIs
HybridAnnotate code, generate specEvolving APIs

Templates and detailed worked examples

Full template library and detailed worked examples live in references/details.md. Read that file when you need the concrete templates.

Best Practices

Do's
  • Use $ref - Reuse schemas, parameters, responses
  • Add examples - Real-world values help consumers
  • Document errors - All possible error codes
  • Version your API - In URL or header
  • Use semantic versioning - For spec changes
Don'ts
  • Don't use generic descriptions - Be specific
  • Don't skip security - Define all schemes
  • Don't forget nullable - Be explicit about null
  • Don't mix styles - Consistent naming throughout
  • Don't hardcode URLs - Use server variables

© wshobson, MIT. 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 plugins/documentation-generation/skills/openapi-spec-generation of wshobson/agents.

  • SKILL.md
  • references/code-first-and-tooling.md
  • references/details.md

Open the folder on GitHubat commit 46891e7

Used in 9 other repositories

We found 32 copies of this SKILL.md (exact, near-identical or edited) in other folders, from 9 other GitHub owners. This page covers the copy in wshobson/agents, which our catalogue first saw on October 7, 2026.

Compare with similar skills

OpenAPI Spec Generation 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.

OpenAPI Spec Generation compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
OpenAPI Spec Generation this skillwshobson/agents40k9 repos~511Automated safety check: PassMIT
API Design Assistantmajiayu000/claude-skill-registry6661 repos~2.7kAutomated safety check: PassMIT
Docs Interfacesjh941213/my-cc-harness126—~863Automated safety check: NotesNone
API Documentation WriterOneWave-AI/claude-skills322—~541Automated safety check: PassMIT
API DesignerJeffallan/claude-skills12k2 repos~2kAutomated safety check: PassMIT
Old Coder API DesignAmazingAng/old-coder7491 repos~3.4kAutomated safety check: PassMIT

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Works with

Categories

Questions about OpenAPI Spec Generation

What does OpenAPI Spec Generation do?

Create, validate and maintain OpenAPI 3.1 specs for REST APIs, whether designed first or generated from existing code, and use them for docs and client SDKs. 1 specifications for RESTful APIs and keeping them accurate. It compares three approaches: design-first, where the spec is written before the code; code-first, where the spec is generated from an existing API; and a hybrid in which annotated code produces the spec.

When should I use OpenAPI Spec Generation?

OpenAPI Spec Generation fits situations like: writing an API contract before implementation starts; generating an OpenAPI spec from an existing REST service; checking that an API implementation matches its spec; producing client SDKs or a docs portal from a spec.

How do I install OpenAPI Spec Generation in Claude Code?

Run `npx skills add wshobson/agents --skill openapi-spec-generation -a claude-code`. Or copy the skill folder (plugins/documentation-generation/skills/openapi-spec-generation in wshobson/agents) into .claude/skills/openapi-spec-generation in your project. Claude Code loads it when a task matches its description.

How do I install OpenAPI Spec Generation in Codex?

Run `npx skills add wshobson/agents --skill openapi-spec-generation -a codex`. Or copy the skill folder (plugins/documentation-generation/skills/openapi-spec-generation in wshobson/agents) into .agents/skills/openapi-spec-generation in your project. Codex loads it when a task matches its description.

Can I use OpenAPI Spec Generation 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 wshobson/agents --skill openapi-spec-generation -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/openapi-spec-generation, .gemini/skills/openapi-spec-generation, .github/skills/openapi-spec-generation and .opencode/skills/openapi-spec-generation in your project.

What does OpenAPI Spec Generation need to run?

SKILL.md names no scripts, command-line tools or credentials: OpenAPI Spec Generation is instructions for the agent only.

Does OpenAPI Spec Generation 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 OpenAPI Spec Generation 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 OpenAPI Spec Generation use?

OpenAPI Spec Generation is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does OpenAPI Spec Generation use?

About 511 tokens (SKILL.md is roughly 2k 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 5.9k tokens, read only when the agent opens those files.

What are the alternatives to OpenAPI Spec Generation?

Skills that share tags, products or a category with OpenAPI Spec Generation: API Design Assistant (majiayu000/claude-skill-registry, 666 stars), Docs Interfaces (jh941213/my-cc-harness, 126 stars), API Documentation Writer (OneWave-AI/claude-skills, 322 stars) and API Designer (Jeffallan/claude-skills, 12k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains OpenAPI Spec Generation?

wshobson (a GitHub user) maintains it in wshobson/agents, which has 40,254 GitHub stars. The repository holds 142 skills in this directory. The repository was last updated on October 5, 2026.

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