openapi-spec-generator

OpenAPI / Swagger Specification Generator

Generate complete, valid OpenAPI 3.x or Swagger 2.0 specifications from descriptions, code, or partial specs.

Workflow

Step 1 — Gather Context

Before writing any YAML/JSON, ask (or infer from context) the following:

Question	Why it matters
OpenAPI 3.x or Swagger 2.0?	Different info, servers/host, components/definitions structure
Output format: YAML or JSON?	YAML default unless user specifies JSON
What does this API do?	Sets info.title, info.description, tags
List of endpoints (or code to extract from)?	Core paths object
Authentication type(s)?	securitySchemes — see reference
Common data models or entities?	components/schemas / definitions
Any existing partial spec to extend?	Merge rather than overwrite

If the user provides code (Express routes, FastAPI, Django URLs, Spring controllers, etc.), extract endpoints automatically — do not ask what the user already told you.

Step 2 — Build the Spec

Follow the structure guide for the chosen version. Always produce a complete, valid spec — never leave placeholder comments like # TODO: add schema.

OpenAPI 3.x Skeleton

openapi: "3.1.0"
info:
  title: <API Title>
  version: "1.0.0"
  description: <Short description>
  contact:
    name: <Team or Author>
    email: <[email protected]>
servers:
  - url: https://api.example.com/v1
    description: Production
  - url: https://staging-api.example.com/v1
    description: Staging
tags:
  - name: <Tag>
    description: <Tag description>
paths:
  /resource:
    get:
      summary: List resources
      operationId: listResources
      tags: [<Tag>]
      parameters: []
      responses:
        "200":
          description: Success
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/ResourceList"
              example:
                items: []
                total: 0
        "401":
          $ref: "#/components/responses/Unauthorized"
        "500":
          $ref: "#/components/responses/InternalError"
      security:
        - BearerAuth: []
components:
  schemas: {}
  responses:
    Unauthorized:
      description: Authentication required
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/Error"
    InternalError:
      description: Internal server error
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/Error"
  securitySchemes: {}