Sequential Media Types

OpenAPI 3.2+

OpenAPI 3.2 introduces support for sequential and streaming media types, enabling description of data streams where individual items arrive over time.

New Schema Field: itemSchema

The key addition is the itemSchema field, which describes the structure of a repeated item in a response:

# OpenAPI 3.2
responses:
  '200':
    description: Stream of updates
    content:
      text/event-stream:
        itemSchema:
          type: object
          properties:
            id: { type: string }
            data: { type: object }

Supported Sequential Media Types

OpenAPI 3.2 adds support for several streaming formats:

• Server-Sent Events: text/event-stream
• JSON Lines: application/jsonl
• JSON Sequences: application/json-seq
• Multipart Mixed: multipart/mixed

Enhanced Multipart Support

OpenAPI 3.2 introduces new encoding fields for multipart content:

itemEncoding

Applies encoding to each item in a sequence:

# OpenAPI 3.2
content:
  multipart/form-data:
    itemEncoding:
      file:
        contentType: application/octet-stream

prefixEncoding

Specifies encoding for items by position:

# OpenAPI 3.2
content:
  multipart/mixed:
    prefixEncoding:
      - contentType: application/json
      - contentType: text/html

Sequential media type support in OpenAPI 3.2 enables documentation of streaming and real-time APIs using the itemSchema field to describe individual items in data streams.