Extending the REST API 
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Guides Guides
Modifying responses: add fields to REST API response objects using register_rest_field
Adding Endpoints: create custom REST API endpoints for your plugin or application
Working with Custom Content Types: learn how to interact with your custom post types and custom taxonomies through the REST API
Resources Resources
Defining your API Schema: define the schema for your REST API resources and their arguments
Glossary: get up to speed with phrases used throughout our documentation
Routes & Endpoints: dive deeper into the nuances of REST API routes and the endpoints they provide
Controller Classes: discover how to structure and extend REST API endpoint controller classes