OpenAPI configuration

OpenAPI is a popular format for describing an API. An OpenAPI file can be used by various tools to generate documentation for the API or even basic client-side bindings for dozens of programming languages.

Zulip’s API is described in zerver/openapi/zulip.yaml. Our aim is for that file to fully describe every endpoint in the Zulip API, and for the Zulip test suite to fail should the API every change without a corresponding adjustment to the documentation. In particular, essentially all content in Zulip’s REST API documentation is generated from our OpenAPI file.

In an OpenAPI Swagger file, every configuration section is an object. Objects may contain other objects, or reference objects defined elsewhere. Larger API specifications may be split into multiple files. See the OpenAPI specification.

This library isn’t in production use yet, but it is our current plan for how Zulip’s API documentation will work.

Working with the zulip.yaml file

An OpenAPI specification file has three general parts: information and configuration, endpoint definitions, and object schemas referenced by other objects (as an alternative to defining everything inline.) References can either specify an individual object, using $ref:, or compose a larger definition from individual objects with allOf: (which may itself contain a $ref.)


These objects, at the top of zulip.yaml, identify the API, define the backend host for the working examples, list supported schemes and types of authentication, and configure other settings. Once defined, information in this section rarely changes.

For example, the swagger and info objects look like this:

# Basic Swagger UI info
openapi: 3.0.1
  version: 1.0.0
  title: Zulip REST API
  description: Powerful open source group chat.
    name: Apache 2.0

Endpoint definitions

The Paths Object contains Path Item Objects for each endpoint. It describes in detail the methods and parameters the endpoint accepts and responses it returns.

There is one Path Item Object for each supported method, containing a Parameters Definition Object describing the required and optional inputs. A Response Object similarly specifies the content of the response. They may reference schemas from a global Definitions Object (see Schemas, below.)


The /users/{user}/presence endpoint (defined in a Path Item Object) expects a GET request with one parameter, HTTP Basic authentication, and returns a JSON response containing msg, result, and presence values.

    description: Get presence data for another user.
    operationId: getPresence
    - name: user
      in: path
      description: Enter email address
      required: true
      type: string
    - basicAuth: []
        description: The response from a successful call
          type: object
          - msg
          - result
          - presence
              type: string
              type: string
              type: array


The Definitions Object contains schemas referenced by other objects. For example, MessageResponse, the response from the /messages endpoint, contains three required parameters. Two are strings, and one is an integer.

  type: object
    - msg
    - result
    - id
      type: string
      type: string
      type: integer
      format: int64

You can find more examples, including GET requests and nested objects, in zerver/openapi/zulip.yaml.

Zulip Swagger YAML style:

We’re collecting decisions we’ve made on how our Swagger YAML files should be organized here:

  • Use shared definitions and YAML anchors to avoid duplicating content where possible.

Tips for working with YAML:

You can edit YAML files in any text editor. Indentation defines blocks, so whitespace is important (as it is in Python.) TAB characters are not permitted. If your editor has an option to replace tabs with spaces, this is helpful.

You can also use the Swagger Editor, which validates YAML and understands the Swagger specification. Download and run it locally, or use the online version. If you aren’t using a YAML-aware editor, make small changes and check your additions often.

Note: if you are working with Swagger UI in a local development environment, it uses an online validator that must be able to access your file. You may see a red “ERROR” button at the bottom of your API docs page instead of the green “VALID” one even if your file is correct.

Formatting help:

  • Comments begin with a # character.

  • Descriptions do not need to be in quotes, and may use common Markdown format options like inline code ` (backtick) and # headings.

  • A single | (pipe) character begins a multi-line description on the next line. Single spaced lines (one newline at the end of each) are joined. Use an extra blank line for a paragraph break. We prefer to use this format for all descriptions because it doesn’t require extra effort to expand.


Description: |
             This description has multiple lines.
             Sometimes descriptions can go on for
             several sentences.

             A description might have multiple paragraphs
             as well.