Enabling JSON lines responses

JSON Lines (JSONL) or Newline Delimited JSON (NDJSON) is a simple and efficient format for streaming structured data. Each line in the stream is a valid JSON object, making it ideal for streaming large datasets, log files, or real-time data feeds. This format is particularly useful for processing data line by line without loading the entire response into memory.

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The format is known by two names and content types, which are completely interchangeable:

JSON Lines (JSONL): application/jsonl
Newline Delimited JSON (NDJSON): application/x-ndjson

Either content type can be used in the OpenAPI specification, as they are functionally identical (each line must be a valid JSON object that matches the specified schema).

Here’s an example of using an SDK to stream log data in JSONL/NDJSON format:

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The JSONL/NDJSON streaming feature is currently supported in TypeScript, Python, Go, and Java. Let us know if you’d like to see support for other languages.

Modeling JSONL/NDJSON in OpenAPI

To implement line-delimited JSON streaming in generated SDKs, model an API endpoint that serves a stream in the OpenAPI document. Each line in the response will be a JSON object matching the specified schema. Either application/jsonl or application/x-ndjson can be used as the content type.

Basic implementation

The example below shows an operation that streams log events:


paths:
  /logs:
    get:
      summary: Stream log events
      operationId: stream
      tags:
        - logs
      parameters:
        - name: query
          in: query
          required: true
          schema:
            type: string
      responses:
        "200":
          description: Log events stream
          content:
            # Either content type can be used:
            application/jsonl:
              schema:
                $ref: "#/components/schemas/LogEvent"
            # OR
            application/x-ndjson:
              schema:
                $ref: "#/components/schemas/LogEvent"
components:
  schemas:
    LogEvent:
      description: A log event in line-delimited JSON format
      type: object
      properties:
        timestamp:
          type: string
        message:
          type: string

Endpoints with multiple response types

For APIs that support both batch and streaming responses, use URL fragments to define separate paths for each response type:


paths:
  /analytics:
    get:
      summary: >
        Get analytics events as a batch response
      operationId: getBatch
      tags: [analytics]
      parameters:
        - name: start_date
          in: query
          required: true
          schema:
            type: string
            format: date
      responses:
        "200":
          description: Analytics events batch
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: "#/components/schemas/AnalyticsEvent"
  /analytics#stream:
    get:
      summary: >
        Stream analytics events in real-time
      operationId: stream
      tags: [analytics]
      parameters:
        - name: start_date
          in: query
          required: true
          schema:
            type: string
            format: date
      responses:
        "200":
          description: Analytics events stream
          content:
            application/x-ndjson:
              schema:
                $ref: "#/components/schemas/AnalyticsEvent"

Use the appropriate method based on the requirements:

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Last updated on September 16, 2025