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3. Chapter 4: OpenAPI spec and generated reference docs

Step 4: The paths object (OpenAPI tutorial)

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The paths object contains the meat of your API information. The paths object has several sub-objects: a path items object, an operations object, and more.

We’ve been moving along at about 5 mph in the previous steps but are going to speed up to 60 mph here quickly. It’s okay if the content that follows doesn’t entirely sink in. You can paste the example code that follows into Swagger UI for now and later go back to study it in more detail.

• Paths objects
  • Operation Objects
    • Parameters object
    • Responses object
• Paths object code
• View the Appearance in Swagger UI
• Note about parameter dependencies

Paths objects

My preferred term is “endpoint” rather than “path,” but to be consistent with the terminology of the OpenAPI spec, I use the term “paths” here.

Each item in the path object contains an operation object. (Operations are the GET, POST, PUT, and DELETE methods we explored in the Endpoints section of the API reference tutorial.)

Start by listing the paths (endpoints) and their allowed operations (methods). For the weather endpoint in the OpenWeatherMap API, there is just one path (/weather) and one operation (get) for that path:

paths:
  /weather:
    get:

Operation Objects

The operation object (get in the code above) contains various properties and objects:

• tags: A group name to organize paths in the Swagger UI. Swagger UI will group endpoints under tag headings.
• summary: A brief overview of the path. Swagger UI shows the summary next to the path name. Limit the summary to 5-10 words only. The display appears even when this section is collapsed.
• description: A full description of the path. Include as much detail as you want. There’s a lot of space in the Swagger UI for these details. CommonMark Markdown is allowed.
• externalDocs (object): Links to documentation for more information about the path.
• operationId: A unique identifier for the path.
• parameters (object): Parameters accepted by the path. Does not include request bodies, which are instead detailed in the requestBody object. The parameters object can also include a reference object that contains a pointer to the description in the components object (this is explained in Step 5: The components object).
• requestBody (object): The request body details for this path. The requestBody object can also include a reference object that contains a pointer to the description in the components object (explained in step 5). (You can find an example of a requestBody parameter in the Swagger Petstore demo. The /pet endpoint submits a request body when adding a pet. Check out the requestBody YAML syntax in petstore-expanded.yml — look at post under /pets. Also see Describing Request Body.)
• responses (object): Responses provided from requests with this path. The responses object can also include a reference object that contains a pointer to the description in the components object. Responses use standard status codes.
• callbacks (object): Callback details to be initiated by the server if desired. Callbacks are operations performed after a function finishes executing. The callbacks object can also include a reference object that contains a pointer to the description in the components object.
• deprecated: Whether the path is deprecated. Omit unless you want to indicate a deprecated field. Boolean.
• security (object): Security authorization method used with the operation. Include this object at the path level only if you want to overwrite the security object at the root level. The name is defined by the securitySchemes object in the components object. More details about this are provided in the security object.
• servers (object): A servers object that might differ from the global servers object for this path.

Each of the above hyperlinked properties that say “(object)” contain additional levels. Their values aren’t just simple data types like strings but are rather objects that contain their own properties.

You’ll undoubtedly need to consult the OpenAPI spec to see what details are required for each of the values and objects here. I can’t replicate all the details you need, nor would I want to. I’m just trying to introduce you to the OpenAPI properties at a surface level.

Let’s add a skeleton of the operation object details to our existing code:

paths:
  /weather:
    get:
      tags:
      summary:
      description:
      operationId:
      externalDocs:
      parameters:
      responses:
      deprecated:
      security:
      servers:
      requestBody:
      callbacks:

At this point, if you paste this content into the Swagger Editor, you will get errors until some additional properties are added.

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Now we can remove a few unnecessary fields that we don’t need for our OpenWeatherMap API documentation:

• There’s no need to include requestBody object because none of the OpenWeatherMap API paths contain request bodies.
• There’s no need to include the servers object because the paths use the same global servers URL that we defined globally at the root level.
• There’s no need to include security because all the paths use the same security object, which we will define globally at the root level later (see Step 6: The security object).
• There’s no need to include deprecated because none of the paths are deprecated.
• There’s no need to include callbacks because none of the paths use callbacks.

As a result, we can reduce the number of relevant fields to the following:

paths:
  /weather:
    get:
      tags:
      summary:
      description:
      operationId:
      externalDocs:
      parameters:
      responses:

Most of the properties for the operation object either require simple strings or include relatively simple objects. The most detailed object here is the parameters object and the responses object.

Parameters object

The parameters object contains an array with these properties:

• name: Parameter name.
• in: Where the parameter appears. Possible values are header, path, query, or cookie. (Request bodies are not described here.)
• description: Description of the parameter.
• required: Whether the parameter is required.
• deprecated: Whether the parameter is deprecated.
• allowEmptyValue: Whether the parameter allows an empty value to be submitted.
• style: How the parameter’s data is serialized (converted to bytes during data transfer).
• explode: Advanced parameter related to arrays.
• allowReserved: Whether reserved characters are allowed.
• schema (object): The schema or model for the parameter. The schema defines the input or output data structure. Note that the schema can also contain an example object.
• example: An example of the media type. If your examples object contains examples, those examples appear in Swagger UI rather than the content in the example object.
• examples (object): An example of the media type, including the schema.

Here’s the paths object that includes the parameters details:

paths:
  /weather:
    get:
      tags:
      - Current Weather Data
      summary: "Call current weather data for one location."
      description: "Access current weather data for any location on Earth including over 200,000 cities! Current weather is frequently updated based on global models and data from more than 40,000 weather stations."
      operationId: CurrentWeatherData
      parameters:
      - name: q
        in: query
        description: "**City name**. *Example: London*. You can call by city name, or by city name and country code. The API responds with a list of results that match a searching word. For the query value, type the city name and optionally the country code divided by a comma; use ISO 3166 country codes."
        schema:
          type: string

      - name: id
        in: query
        description: "**City ID**. *Example: `2172797`*. You can call by city ID. The API responds with the exact result. The List of city IDs can be downloaded [here](http://bulk.openweathermap.org/sample/). You can include multiple cities in this parameter — just separate them by commas. The limit of locations is 20. *Note: A single ID counts as a one API call. So, if you have 3 city IDs, it’s treated as 3 API calls.*"
        schema:
          type: string

      - name: lat
        in: query
        description: "**Latitude**. *Example: 35*. The latitude coordinate of the location of your interest. Must use with `lon`."
        schema:
          type: string

      - name: lon
        in: query
        description: "**Longitude**. *Example: 139*. Longitude coordinate of the location of your interest. Must use with `lat`."
        schema:
          type: string

      - name: zip
        in: query
        description: "**Zip code**. Search by zip code. *Example: 95050,us*. Please note that if the country is not specified, the search uses USA as a default."
        schema:
          type: string

      - name: units
        in: query
        description: '**Units**. *Example: imperial*. Possible values: `standard`, `metric`, and `imperial`. When you do not use the `units` parameter, the format is `standard` by default.'
        schema:
          type: string
          enum: [standard, metric, imperial]
          default: "imperial"

      - name: lang
        in: query
        description: '**Language**. *Example: en*. You can use lang parameter to get the output in your language. We support the following languages that you can use with the corresponded lang values: Arabic - `ar`, Bulgarian - `bg`, Catalan - `ca`, Czech - `cz`, German - `de`, Greek - `el`, English - `en`, Persian (Farsi) - `fa`, Finnish - `fi`, French - `fr`, Galician - `gl`, Croatian - `hr`, Hungarian - `hu`, Italian - `it`, Japanese - `ja`, Korean - `kr`, Latvian - `la`, Lithuanian - `lt`, Macedonian - `mk`, Dutch - `nl`, Polish - `pl`, Portuguese - `pt`, Romanian - `ro`, Russian - `ru`, Swedish - `se`, Slovak - `sk`, Slovenian - `sl`, Spanish - `es`, Turkish - `tr`, Ukrainian - `ua`, Vietnamese - `vi`, Chinese Simplified - `zh_cn`, Chinese Traditional - `zh_tw`.'
        schema:
          type: string
          enum: [ar, bg, ca, cz, de, el, en, fa, fi, fr, gl, hr, hu, it, ja, kr, la, lt, mk, nl, pl, pt, ro, ru, se, sk, sl, es, tr, ua, vi, zh_cn, zh_tw]
          default: "en"

      - name: mode
        in: query
        description: "**Mode**. *Example: html*. Determines the format of the response. Possible values are `xml` and `html`. If the mode parameter is empty, the format is `json` by default."
        schema:
          type: string
          enum: [json, xml, html]
          default: "json"

If you get stuck, see the sample OpenAPI spec here for the fully working sample. This will help you spot and troubleshoot indentation or other errors.

Responses object

About Tom Johnson

I'm an API technical writer based in the Seattle area. On this blog, I write about topics related to technical writing and communication — such as software documentation, API documentation, AI, information architecture, content strategy, writing processes, plain language, tech comm careers, and more. Check out my API documentation course if you're looking for more info about documenting APIs. Or see my posts on AI and AI course section for more on the latest in AI and tech comm.

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