https://qiita.com/HawkClaws/items/599d7666f55e79ef7f56 のapidoc

openapi.yml

openapi: 3.0.1
info:
  title: エンジニア・プログラマにしか使えないSNS
  description: |
    通常のSNSで胡散臭い人が多いと感じてしまいました
    プログラミングスクールが流行り、エンジニアになって億稼いでます！みたいな・・・
    
    そこで、本当のエンジニア・プログラマしか使えないSNSを作ってみました！
    つまり、WebApi提供のみのSNSです
    一般ピープルが使うようなフロントエンドなんてありません！！
    Postmanなり、なんなりを使って叩いてください"
  version: 1.0.0
externalDocs:
  description: "元記事: エンジニア・プログラマにしか使えないSNSを作ってみた話"
  url: https://qiita.com/HawkClaws/items/599d7666f55e79ef7f56
servers:
- url: https://versatileapi.herokuapp.com/api
paths:
  /user/create_user:
    post:
      summary: ユーザ登録
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUserRequest'
      responses:
        201:
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  id:
                    type: string
                    description: ユーザID

    put:
      summary: ユーザ情報更新（なのにユーザIDを指定しない？！全項目必須？！）
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUserRequest'
      responses:
        200:
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  id:
                    type: string
                    description: ユーザID
  /user/{id}:
    get:
      summary: ユーザ取得（単一）
      parameters:
      - name: id
        in: path
        description: ユーザID
        required: true
        schema:
          type: string
      responses:
        200:
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/User'
  /user/all:
    get:
      summary: ユーザ一覧取得
      responses:
        200:
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/User'

  /text:
    post:
      summary: つぶやく
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/TextRequest'
      responses:
        201:
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  id:
                    type: string
                    description: TextID

  /text/{id}:
    get:
      summary: つぶやき取得（単一）
      parameters:
      - name: id
        in: path
        description: TextID
        required: true
        schema:
          type: string
      responses:
        200:
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Text'
  /text/all:
    get:
      summary: つぶやき一覧取得
      responses:
        200:
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Text'

components:
  schemas:
    CreateUserRequest:
      type: object
      properties:
        name:
          type: string
          description: ユーザ名
          maxLength: 30
        description:
          type: string
          description: 自己紹介文
          maxLength: 300
      required:
      - name
      - description
    User:
      type: object
      properties:
        id:
          type: string
          description: ユーザID
        name:
          type: string
          description: ユーザ名
        description:
          type: string
          description: 自己紹介文
        _user_id:
          type: string
          description: ユーザID
        _created_at:
          type: string
          description: 登録日時
        _updated_at:
          type: string
          description: 最終更新日時
    TextRequest:
      type: object
      properties:
        text:
          type: string
          description: 投稿する文章
          minLength: 1
          maxLength: 280
        in_reply_to_user_id:
          type: string
          description: 返信対象のUserId
          minLength: 40
          maxLength: 40
        in_reply_to_text_id:
          type: string
          description: 返信対象のTextId
          minLength: 36
          maxLength: 36
      required:
      - text
      - description
    Text:
      type: object
      properties:
        id:
          type: string
          description: TextID
        text:
          type: string
          description: つぶやき
        in_reply_to_user_id:
          type: string
          description: 返信対象のUserId
        in_reply_to_text_id:
          type: string
          description: 返信対象のTextId
        _user_id:
          type: string
          description: ユーザID
        _created_at:
          type: string
          description: 投稿日時
        _updated_at:
          type: string
          description: 最終更新日時

  securitySchemes:
    authorization_helloworld:
      type: apiKey
      in: header
      name: Authorization

https://bit.ly/39hZjMB

or

https://editor.swagger.io/?url=https://gist.githubusercontent.com/YusukeIwaki/ce8a7250fb7e5279267c495324de19f7/raw/292eb24fb381c9af49fc42c901794ec2d98d134a/openapi.yml