MCP Adapter

Part of the AI Building Blocks for WordPress initiative

The official WordPress package for MCP integration that exposes WordPress abilities as Model Context Protocol (MCP) tools, resources, and prompts for AI agents.

Overview

This adapter bridges WordPress's Abilities API with the MCP specification, providing a standardized way for AI agents to interact with WordPress functionality. It includes HTTP and STDIO transport support, comprehensive error handling, and an extensible architecture for custom integrations.

Features

Core Functionality

• Ability-to-MCP Conversion: Automatically converts WordPress abilities into MCP tools, resources, and prompts
• Multi-Server Management: Create and manage multiple MCP servers with unique configurations
• Extensible Transport Layer:
  • HTTP Transport: Unified transport implementing MCP 2025-11-25 specification for HTTP-based communication
  • STDIO Transport: Process-based communication via standard input/output for local development and CLI integration
  • Custom Transport Support: Implement McpTransportInterface to create specialized communication protocols
  • Multi-Transport Configuration: Configure servers with multiple transport methods simultaneously
• Flexible Error Handling:
  • Built-in Error Handler: Default WordPress-compatible error logging included
  • Custom Error Handlers: Implement McpErrorHandlerInterface for custom logging, monitoring, or notification systems
  • Server-specific Handlers: Different error handling strategies per MCP server
• Observability:
  • Built-in Observability: Default zero-overhead metrics tracking with configurable handlers
  • Custom Observability Handlers: Implement McpObservabilityHandlerInterface for integration with monitoring systems
• Validation: Built-in validation for tools, resources, and prompts with extensible validation rules
• Permission Control: Granular permission checking for all exposed functionality with configurable transport permissions

MCP Component Support

• Tools: Convert WordPress abilities into executable MCP tools for AI agent interactions
• Resources: Expose WordPress data as MCP resources for contextual information access
• Prompts: Transform abilities into structured MCP prompts for AI guidance and templates
• Server Discovery: Automatic registration and discovery of MCP servers following MCP protocol standards
• Built-in Abilities: Core WordPress abilities for system introspection and ability management
• CLI Integration: WP-CLI commands supporting STDIO transport as defined in MCP specification

Architecture

For a full breakdown of the component structure, see the Architecture Overview.

Dependencies

• PHP: >= 7.4
• WordPress: >= 6.9 (includes the Abilities API in core — no separate plugin)
• php-mcp-schema (^0.1.0): Typed DTOs for MCP protocol types

Installation

MCP Adapter is distributed as a WordPress plugin. Install and activate it like any other plugin. The release ships with everything it needs, so there is no autoloader to wire up and no build step to run.

Requires WordPress 6.9 or newer; the Abilities API is part of core, so there is no separate plugin to install.

Manually

Download the latest stable mcp-adapter.zip from the GitHub Releases page, then upload it from Plugins → Add Plugin → Upload Plugin and activate it.

With WP-CLI

wp plugin install https://github.com/WordPress/mcp-adapter/releases/latest/download/mcp-adapter.zip --activate

With WP-Env

// .wp-env.json
{
  "$schema": "https://schemas.wp.org/trunk/wp-env.json",
  "plugins": [
    "https://github.com/WordPress/mcp-adapter/releases/latest/download/mcp-adapter.zip"
  ]
}

As a dependency of your plugin

The WP\MCP classes are provided by the MCP Adapter plugin, so declare it as a plugin dependency using the Requires Plugins field in your plugin header:

<?php
/**
 * Plugin Name:      My Plugin
 * Description:      Adds MCP tools for my feature.
 * Requires Plugins: mcp-adapter
 */

Using MCP Adapter in Your Plugin

Check availability and initialize on plugins_loaded so all plugins are available before the adapter starts:

add_action( 'plugins_loaded', function() {
    if ( ! class_exists( 'WP\MCP\Core\McpAdapter' ) ) {
        // MCP Adapter is not active — show an admin notice or return early.
        return;
    }

    \WP\MCP\Core\McpAdapter::instance();
} );

Basic Usage

The MCP Adapter automatically creates a default server that exposes registered WordPress abilities through a layered architecture. This provides immediate MCP functionality without requiring manual server configuration.

How it works:

• WordPress abilities registered via wp_register_ability() with meta.public set to true are discoverable and executable on the default server via its built-in adapter tools
• Set meta.mcp.public explicitly to override the high-level setting for MCP only; false opts a public ability out, while true exposes an otherwise private ability to MCP
• On the default server, public abilities are accessed through mcp-adapter/discover-abilities, mcp-adapter/get-ability-info, and mcp-adapter/execute-ability rather than being auto-registered individually in tools/list
• Alternatively, abilities can be explicitly listed when creating a custom MCP server; in that case, they can be exposed directly as MCP tools, resources, or prompts without requiring the meta.mcp.public flag
• The default server supports both HTTP and STDIO transports and supports multiple MCP protocol versions
• Built-in error handling and observability are included
• Access via HTTP: /wp-json/mcp/mcp-adapter-default-server
• Access via STDIO: wp mcp-adapter serve --server=mcp-adapter-default-server

// Simply register a WordPress ability
add_action( 'wp_abilities_api_init', function() {
    wp_register_ability( 'my-plugin/get-posts', [
        'label' => 'Get Posts',
        'description' => 'Retrieve WordPress posts with optional filtering',
        'category' => 'site',
        'input_schema' => [
            'type' => 'object',
            'properties' => [
                'numberposts' => [
                    'type' => 'integer',
                    'description' => 'Number of posts to retrieve',
                    'default' => 5,
                    'minimum' => 1,
                    'maximum' => 100
                ],
                'post_status' => [
                    'type' => 'string',
                    'description' => 'Post status to filter by',
                    'enum' => ['publish', 'draft', 'private'],
                    'default' => 'publish'
                ]
            ]
        ],
        'output_schema' => [
            'type' => 'array',
            'items' => [
                'type' => 'object',
                'properties' => [
                    'ID' => ['type' => 'integer'],
                    'post_title' => ['type' => 'string'],
                    'post_content' => ['type' => 'string'],
                    'post_date' => ['type' => 'string'],
                    'post_author' => ['type' => 'string']
                ]
            ]
        ],
        'execute_callback' => function( $input ) {
            $args = [
                'numberposts' => $input['numberposts'] ?? 5,
                'post_status' => $input['post_status'] ?? 'publish'
            ];
            return get_posts( $args );
        },
        'permission_callback' => function() {
            return current_user_can( 'read' );
        },
        'meta' => [
            'public' => true, // Expose to clients, including the default MCP server
        ],
    ]);
});

// With the meta.public flag, the ability is exposed through the default MCP server.
// In the default server configuration, discover it via `discover-abilities`
// and invoke it via `mcp-adapter/execute-ability` rather than expecting
// it to appear as its own entry in `tools/list`.
// To opt out of MCP while remaining public to other clients, explicitly set
// meta.mcp.public to false.
// To expose only through MCP, omit `meta.public` and set `meta.mcp.public` to true.
// Without either public flag, abilities are only accessible through custom MCP
// servers that explicitly list them.
// Note: how far `meta.public` reaches depends on the WordPress version. WordPress
// core starts applying `meta.public` to the REST API (`meta.show_in_rest`) in 7.1. On
// WordPress 6.9 and 7.0, this adapter honors `meta.public` for MCP, but REST API
// access still requires setting `meta.show_in_rest` to true.

For detailed information about creating WordPress abilities, see the Abilities API developer documentation.

Connecting to MCP Servers

The MCP Adapter supports multiple connection methods. Here are examples for connecting with MCP clients:

STDIO Transport (Local Development)

For local development and testing, you can interact directly with MCP servers using WP-CLI commands:

# List all available MCP servers
wp mcp-adapter list

# Test the discover abilities tool to see all available WordPress abilities
echo '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"mcp-adapter-discover-abilities","arguments":{}}}' | wp mcp-adapter serve --user=admin --server=mcp-adapter-default-server

# Test listing available tools
echo '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}' | wp mcp-adapter serve --user=admin --server=mcp-adapter-default-server

MCP Client Configuration

Configure MCP clients (Claude Desktop, Claude Code, VS Code, Cursor, etc.) to connect to your WordPress MCP servers.

{
  "mcpServers": {
    "wordpress-default": {
      "command": "wp",
      "args": [
        "--path=/path/to/your/wordpress/site",
        "mcp-adapter",
        "serve",
        "--server=mcp-adapter-default-server",
        "--user=admin"
      ]
    },
    "wordpress-custom": {
      "command": "wp",
      "args": [
        "--path=/path/to/your/wordpress/site",
        "mcp-adapter",
        "serve",
        "--server=your-custom-server-id",
        "--user=admin"
      ]
    }
  }
}

{
  "mcpServers": {
    "wordpress-http-default": {
      "command": "npx",
      "args": [
        "-y",
        "@automattic/mcp-wordpress-remote@latest"
      ],
      "env": {
        "WP_API_URL": "http://your-site.test/wp-json/mcp/mcp-adapter-default-server",
        "LOG_FILE": "/path/to/logs/mcp-adapter.log",
        "WP_API_USERNAME": "your-username",
        "WP_API_PASSWORD": "your-application-password"
      }
    },
    "wordpress-http-custom": {
      "command": "npx",
      "args": [
        "-y",
        "@automattic/mcp-wordpress-remote@latest"
      ],
      "env": {
        "WP_API_URL": "http://your-site.test/wp-json/your-namespace/your-route",
        "LOG_FILE": "/path/to/logs/mcp-adapter.log",
        "WP_API_USERNAME": "your-username",
        "WP_API_PASSWORD": "your-application-password"
      }
    }
  }
}

Advanced Usage

Creating Custom MCP Servers

For advanced use cases, you can create custom MCP servers with specific configurations:

add_action( 'mcp_adapter_init', function( $adapter ) {
    $adapter->create_server(
        'my-server-id',                    // Unique server identifier
        'my-namespace',                    // REST API namespace
        'mcp',                             // REST API route
        'My MCP Server',                   // Server name
        'Description of my server',        // Server description
        'v1.0.0',                          // Server version
        array(                             // Transport methods
            \WP\MCP\Transport\HttpTransport::class,
        ),
        \WP\MCP\Infrastructure\ErrorHandling\ErrorLogMcpErrorHandler::class,        // Error handler
        \WP\MCP\Infrastructure\Observability\NullMcpObservabilityHandler::class,    // Observability handler
        array( 'my-plugin/my-ability' ),   // Abilities to expose as tools
        array(),                           // Resources (optional)
        array()                            // Prompts (optional)
    );
} );

Custom Transport Implementation

The MCP Adapter includes production-ready HTTP transports. For specialized requirements like custom authentication, message queues, or enterprise integrations, you can create custom transport protocols.

See the Custom Transports Guide for detailed implementation instructions.

Custom Transport Permissions

The MCP Adapter supports custom authentication logic through transport permission callbacks. Instead of the default is_user_logged_in() check, you can implement custom authentication for your MCP servers.

See the Transport Permissions Guide for detailed authentication patterns.

Custom Error Handler

The MCP Adapter includes a default WordPress-compatible error handler, but you can implement custom error handling to integrate with existing logging systems, monitoring tools, or meet specific requirements.

See the Error Handling Guide for detailed implementation instructions.

Custom Observability Handler

The MCP Adapter includes built-in observability for tracking metrics and events. You can implement custom observability handlers to integrate with monitoring systems, analytics platforms, or performance tracking tools.

See the Observability Guide for detailed metrics tracking and custom handler implementation.

Migration

• Migration Guide: v0.5.0 — Breaking changes and upgrade instructions
• Migration Guide: v0.3.0 — Transport, observability, and hook name changes

License

GPL-2.0-or-later