API

Overview

Line 21 API enables developers to interact with the system programmatically.

The platform provides a REST API which can be interacted with through HTTP and from any programming language with all requests and responses encoded in JSON format.

The API currently supports two actions with other expanded functionality planned for future releases:

• Caption production: add external captions to a project
• Caption retrieval: download recorded captions for a project in various formats

Authentication

Authentication is based on the usage of a Bearer Token linked to a project.
In your project dashboard navigate to API in the left sidebar and copy the API Key.

Each request must contain an Authentication header with Bearer <api_key> as content.

Note: the API key is unique to the project not to the organisation. This is useful especially if you work with different partners or clients for different projects.

Endpoints

Send your requests to https://caption.line-21.com/api/v1 with JSON-encoded payloads.
For comprehensive endpoint documentation, request/response schemas, and interactive examples, visit the complete API documentation.

Example request

You can see an example using cURL from command line

curl -X POST "https://caption.line-21.com/api/v1/captions" \
  -H 'accept: application/json'\
  -H 'authorization: Bearer <your_api_key>'\
  -H 'content-type: application/json' \
  -d '{"projectId":"prj-id-123","language":"en","text":"The lazy fox...","timestampStart":1687344200000,"timestampEnd":1687344250000,"isInterim":false}'

Future plans

We're actively expanding the API to provide complete programmatic control over the Line 21 platform. Upcoming features include:

• Organization and project management endpoints
• Organization-level API keys with granular permissions
• Multi-key support for enhanced security and access control
• Full coverage of all platform capabilities