Day 29: REST API Parameters and WP CLI

WordPress REST API serves as the gateway for communication between your website and the vast world of the internet. In this blog post, we’ll delve into the technicalities of WP REST API’s global parameters like _fields, _embed, _envelope, _methods, and _jsonp. Additionally, we’ll explore methods for adding custom data to your API responses, providing a comprehensive understanding of these features.

Global Parameters (meta-parameters)

1. _fields

  • Definition: _fields allows you to limit the fields returned in the API response, tailoring it to include only the necessary information.
  • Example:
  GET /wp-json/wp/v2/posts?_fields=id,title,date

2. _embed

  • Definition: _embed expands the response by including embedded data related to the requested resource, providing additional details without making extra API calls.
  • Example:
  GET /wp-json/wp/v2/posts?_embed=author

3. _envelope

  • Definition: _envelope wraps the API response in an envelope, providing metadata about the request, such as the HTTP status code.
  • Example:
  GET /wp-json/wp/v2/posts?_envelope

4. _methods

  • Definition: _methods restricts the allowed HTTP methods for a particular endpoint, enhancing security and controlling access.
  • Example:
  GET /wp-json/wp/v2/posts?_methods=GET,POST

5. _jsonp

  • Definition: _jsonp enables JSONP support, allowing cross-origin requests in scenarios where traditional cross-origin resource sharing (CORS) might not be feasible.
  • Example:
  GET /wp-json/wp/v2/posts?_jsonp=myCallbackFunction

Methods for Adding Custom Data:

1. register_rest_field

  • Definition: register_rest_field is a method for adding custom fields to the REST API response for a specified post type.
  • Example:
          'get_callback'    => 'get_custom_field',
          'update_callback' => null,
          'schema'          => null,

2. register_rest_route

  • Definition: register_rest_route is used to register a custom route in the REST API, allowing you to define custom endpoints and their behavior.
  • Example:
          'methods'  => 'GET',
          'callback' => 'custom_endpoint_callback',

3. register_rest_object_type

  • Definition: register_rest_object_type registers a new type of object that can be exposed via the REST API.
  • Example:
          'get_callback'    => 'get_book',
          'update_callback' => 'update_book',


  1. Efficiency: Global parameters like _fields and _embed allow developers to retrieve only the necessary data, optimizing API responses.
  2. Customization: Adding custom data through methods like register_rest_field and register_rest_route enables developers to tailor API responses according to specific requirements.
  3. Control: Global parameters such as _methods offer control over the allowed HTTP methods, enhancing security measures.


  1. Complexity: For beginners, understanding and implementing global parameters and custom data methods may initially seem complex.
  2. Overhead: The use of certain global parameters, especially when unnecessary, may introduce additional overhead in API responses.
  3. Learning Curve: Exploring custom data methods and their parameters may require time and experimentation to grasp effectively.


WP-CLI serves as a powerful command-line interface for managing various aspects of your WordPress site.

Core Commands:

1. wp core install

  • Definition: wp core install is used for installing WordPress via the command line, allowing you to set up the database, configure the site, and perform the initial setup.
  • Example:
wp core install --title="My WordPress Site" --admin_user=admin --admin_password=admin123 [email protected]

2. wp core update

  • Definition: wp core update is employed to update the WordPress core to the latest version, ensuring your site benefits from the latest features and security patches.
  • Example:
  wp core update

3. wp core check-update

  • Definition: wp core check-update allows you to check for updates to the WordPress core without initiating the update process.
  • Example:
  wp core check-update

4. wp core download

  • Definition: wp core download downloads the WordPress core files without installing them, useful for preparing for a manual installation or setting up a development environment.
  • Example:
  wp core download --version=5.9

5. wp core verify-checksums

  • Definition: wp core verify-checksums verifies the integrity of the WordPress core files by comparing them against the checksums provided by
  • Example:
  wp core verify-checksums

Methods for Customization:

1. Creating Custom Commands

  • Definition: Developers can create custom commands by defining their functions and registering them with WP-CLI, extending the command-line functionality.
  • Example:
   * Custom WP-CLI command to perform a specific task.
   * @when before_wp_load
  function my_custom_command() {
      WP_CLI::success( 'Custom command executed successfully!' );
  WP_CLI::add_command( 'my-custom-command', 'my_custom_command' );

2. Global Parameters

  • Definition: Global parameters in WP-CLI allow you to customize command behavior across different commands, providing consistency and flexibility.
  • Example:
  wp --info

3. Configuration Files

  • Definition: WP-CLI supports the use of configuration files (wp-cli.yml) to define command defaults, including options, paths, and behavior.
  • Example:
  core install:
    title: My WordPress Site
    admin_user: username
    admin_password: admin123
    admin_email: [email protected]

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