What is openapi-spec-writer?

A writing skill for OpenAPI 3.0 and 3.1, formats that describe how REST APIs work. It produces API specifications covering routes, data shapes, authentication, examples, and errors.

Use it to design or document REST APIs, migrate older Swagger specifications, generate client SDKs, set up API documentation, and validate responses.

It gives developers and client applications a shared contract for an API, reducing misunderstandings between API design, implementation, and documentation.

openapi-spec-writer — Skill for Claude Code by curiositech

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 curiositech/some_claude_skills --skill openapi-spec-writer

Clone the repo

git clone --depth 1 https://github.com/curiositech/some_claude_skills

Made for: Claude Code.

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/curiositech/some_claude_skills/openapi-spec-writer/github.svg)](https://agentmods.dev/skills/curiositech/some_claude_skills/openapi-spec-writer)

Your own site

<a href="https://agentmods.dev/skills/curiositech/some_claude_skills/openapi-spec-writer"><img src="https://agentmods.dev/badge/skills/curiositech/some_claude_skills/openapi-spec-writer/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/curiositech/some_claude_skills/openapi-spec-writer"><img src="https://agentmods.dev/badge/skills/curiositech/some_claude_skills/openapi-spec-writer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 54 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 3,684 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. Third-party audits

NVIDIA SkillSpector warn 7 Sept 2026

SkillSpector: 1 finding, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

medium Data Exfiltration · line 103
Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.

How audits are shown

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	$0.00054	$0.03684
Opus 5	$0.00027	$0.01842
Sonnet 5	$0.00011	$0.00737
Haiku 4.5	$0.00005	$0.00368

Measured 5d ago against content hash 2db44e4756f2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

openapi-spec-writer 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 5d 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.

.claude/skills/openapi-spec-writer/SKILL.md · 648 lines

How it starts

The opening of the file, as written. The whole thing — 648 lines — stays where its author put it; the contents beside it link to each section on GitHub.

OpenAPI Spec Writer

Overview

Expert in writing OpenAPI 3.0/3.1 specifications for REST APIs. Specializes in schema design, documentation best practices, API-first development, and tooling integration. Generates comprehensive API documentation that serves as both documentation and contract.

When to Use

Creating OpenAPI specifications for new APIs
Documenting existing REST APIs
Designing API contracts before implementation
Generating client SDKs from specs
Setting up interactive API documentation (Swagger UI, Redoc)
Validating API responses against schemas
Migrating from OpenAPI 2.0 (Swagger) to 3.x

Capabilities

Specification Writing

OpenAPI 3.0 and 3.1 syntax
Path and operation definitions
Request/response schemas
Authentication schemes
Server configurations

Schema Design

JSON Schema with OpenAPI extensions
Reusable component schemas
Discriminators for polymorphism
oneOf, anyOf, allOf composition
Nullable types and defaults

Documentation Quality

Meaningful descriptions and examples
Markdown in descriptions
Request/response examples
Error response documentation
Deprecation notices

Tooling Integration

Swagger UI configuration
Redoc customization
Spectral linting rules
SDK generation setup
Mock server configuration

Dependencies

Works well with:

api-architect - API design patterns
rest-api-design - RESTful conventions
typescript-pro - Generated client types
github-actions-pipeline-builder - CI validation

Examples

Complete OpenAPI 3.1 Spec

openapi: 3.1.0
info:
  title: Task Management API
  description: |
    RESTful API for managing tasks and projects.

    ## Authentication
    All endpoints require a Bearer token in the Authorization header.

    ## Rate Limiting
    - 1000 requests per hour per API key
    - Rate limit headers included in all responses
  version: 1.0.0
  contact:
    name: API Support
    email: [email protected]
    url: https://docs.example.com
  license:
    name: MIT
    url: https://opensource.org/licenses/MIT

servers:
  - url: https://api.example.com/v1
    description: Production server
  - url: https://staging-api.example.com/v1
    description: Staging server
  - url: http://localhost:3000/v1
    description: Local development

tags:
  - name: Tasks
    description: Task management operations
  - name: Projects
    description: Project management operations

paths:
  /tasks:
    get:
      operationId: listTasks
      summary: List all tasks
      description: Returns a paginated list of tasks with optional filtering.
      tags:
        - Tasks
      parameters:
        - $ref: '#/components/parameters/PageParam'
        - $ref: '#/components/parameters/LimitParam'
        - name: status
          in: query
          description: Filter by task status
          schema:
            $ref: '#/components/schemas/TaskStatus'
        - name: project_id
          in: query
          description: Filter by project ID
          schema:
            type: string
            format: uuid
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/TaskListResponse'
              examples:
                default:
                  $ref: '#/components/examples/TaskListExample'
          headers:
            X-Total-Count:
              schema:
                type: integer
              description: Total number of tasks matching the query
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'

    post:
      operationId: createTask
      summary: Create a new task
      description: Creates a new task and returns the created resource.
      tags:
        - Tasks
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateTaskRequest'
            examples:
              minimal:
                summary: Minimal task
                value:
                  title: "Complete documentation"
              full:
                summary: Full task with all fields
                value:
                  title: "Complete documentation"
                  description: "Write API docs for v1.0"
                  project_id: "550e8400-e29b-41d4-a716-446655440000"
                  due_date: "2024-12-31"
                  priority: "high"
      responses:
        '201':
          description: Task created successfully
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Task'
          headers:
            Location:
              schema:
                type: string
                format: uri
              description: URL of the created resource
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '422':
          $ref: '#/components/responses/ValidationError'

  /tasks/{taskId}:
    parameters:
      - $ref: '#/components/parameters/TaskIdParam'

    get:
      operationId: getTask
      summary: Get a task by ID
      tags:
        - Tasks
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Task'
        '404':
          $ref: '#/components/responses/NotFound'

    patch:
      operationId: updateTask
      summary: Update a task
      description: Partially updates a task. Only provided fields are updated.
      tags:
        - Tasks
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/UpdateTaskRequest'
      responses:
        '200':
          description: Task updated successfully
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Task'
        '404':
          $ref: '#/components/responses/NotFound'
        '422':
          $ref: '#/components/responses/ValidationError'

    delete:
      operationId: deleteTask
      summary: Delete a task
      tags:
        - Tasks
      responses:
        '204':
          description: Task deleted successfully
        '404':
          $ref: '#/components/responses/NotFound'

components:
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT
      description: JWT token obtained from /auth/login

  parameters:
    TaskIdParam:
      name: taskId
      in: path
      required: true
      description: Unique task identifier
      schema:
        type: string
        format: uuid
      example: "550e8400-e29b-41d4-a716-446655440000"

    PageParam:
      name: page
      in: query
      description: Page number for pagination (1-indexed)
      schema:
        type: integer
        minimum: 1
        default: 1

    LimitParam:
      name: limit
      in: query
      description: Number of items per page
      schema:
        type: integer
        minimum: 1
        maximum: 100
        default: 20

  schemas:
    Task:
      type: object
      required:
        - id
        - title
        - status
        - created_at
        - updated_at
      properties:
        id:
          type: string
          format: uuid
          description: Unique identifier
          readOnly: true
        title:
          type: string
          minLength: 1
          maxLength: 200
          description: Task title
        description:
          type: string
          maxLength: 5000
          description: Detailed task description (supports Markdown)
        status:
          $ref: '#/components/schemas/TaskStatus'
        priority:
          $ref: '#/components/schemas/Priority'
        project_id:
          type: string
          format: uuid
          description: Associated project ID
        due_date:
          type: string
          format: date
          description: Due date (ISO 8601)
        created_at:
          type: string
          format: date-time
          readOnly: true
        updated_at:
          type: string
          format: date-time
          readOnly: true

    TaskStatus:
      type: string
      enum:
        - pending
        - in_progress
        - completed
        - cancelled
      description: Current task status
      default: pending

    Priority:
      type: string
      enum:
        - low
        - medium
        - high
        - urgent
      default: medium

    CreateTaskRequest:
      type: object
      required:
        - title
      properties:
        title:
          type: string
          minLength: 1
          maxLength: 200
        description:
          type: string
          maxLength: 5000
        project_id:
          type: string
          format: uuid
        due_date:
          type: string
          format: date
        priority:
          $ref: '#/components/schemas/Priority'

    UpdateTaskRequest:
      type: object
      minProperties: 1
      properties:
        title:
          type: string
          minLength: 1
          maxLength: 200
        description:
          type: string
          maxLength: 5000
        status:
          $ref: '#/components/schemas/TaskStatus'
        priority:
          $ref: '#/components/schemas/Priority'
        due_date:
          type: string
          format: date

    TaskListResponse:
      type: object
      required:
        - data
        - pagination
      properties:
        data:
          type: array
          items:
            $ref: '#/components/schemas/Task'
        pagination:
          $ref: '#/components/schemas/Pagination'

    Pagination:
      type: object
      required:
        - page
        - limit
        - total
        - total_pages
      properties:
        page:
          type: integer
        limit:
          type: integer
        total:
          type: integer
        total_pages:
          type: integer
        has_next:
          type: boolean
        has_prev:
          type: boolean

    Error:
      type: object
      required:
        - code
        - message
      properties:
        code:
          type: string
          description: Machine-readable error code
        message:
          type: string
          description: Human-readable error message
        details:
          type: object
          additionalProperties: true
          description: Additional error details

    ValidationError:
      allOf:
        - $ref: '#/components/schemas/Error'
        - type: object
          properties:
            errors:
              type: array
              items:
                type: object
                properties:
                  field:
                    type: string
                  message:
                    type: string

  responses:
    BadRequest:
      description: Bad request - invalid parameters
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            code: "BAD_REQUEST"
            message: "Invalid query parameters"

    Unauthorized:
      description: Authentication required
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            code: "UNAUTHORIZED"
            message: "Invalid or expired token"

    NotFound:
      description: Resource not found
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            code: "NOT_FOUND"
            message: "Task not found"

    ValidationError:
      description: Validation failed
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ValidationError'
          example:
            code: "VALIDATION_ERROR"
            message: "Request validation failed"
            errors:
              - field: "title"
                message: "Title is required"

  examples:
    TaskListExample:
      value:
        data:
          - id: "550e8400-e29b-41d4-a716-446655440000"
            title: "Complete documentation"
            status: "in_progress"
            priority: "high"
            created_at: "2024-01-15T10:30:00Z"
            updated_at: "2024-01-15T10:30:00Z"
        pagination:
          page: 1
          limit: 20
          total: 42
          total_pages: 3
          has_next: true
          has_prev: false

security:
  - bearerAuth: []

Read the full file on GitHub · 648 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.

5d ago First seen · 648 lines · 54 tokens per session scan A 2db44e4756f2

Subscribe to this mod's changes

openapi-spec-writer is a skill published in the GitHub repository curiositech/some_claude_skills (216 stars, last pushed 3d ago), licensed MIT. It adds 54 tokens to every session and 3,684 once invoked, about $0.0003 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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