MCP Server Bundle

A powerful Symfony bundle for handling MCP (Message Control Protocol) server implementations, providing tools for JSON-RPC request handling and tool management.
Read the official MCP specification.

[!WARNING]
The specification of the Model Context Protocol (MCP) changes frequently. This bundle will evolve along with the specification, so please ensure you are using the latest version of the bundle.
The CHANGELOG can be found here.

Getting Started

The MCP Server Bundle provides a structured way to create and manage tools that can be used by clients via JSON-RPC requests.
It includes features for MCP tool management, and JSON-RPC method handling.

This bundle is designed to be flexible and extensible, allowing developers to create custom tool handlers and method handlers as needed.
MethodHandlers and ToolHandlers are registered and autowired using attributes, making it easy to define and manage your own tools.

Installation

Install the MCP Server Bundle via Composer:

composer require ecourty/mcp-server-bundle

Add the bundle to your config/bundles.php (if not using Symfony Flex):

return [
    // ...
    Ecourty\McpServerBundle\McpServerBundle::class => ['all' => true],
];

Configure the routes in config/routes/mcp.yaml:

mcp_controller:
  path: /mcp
  controller: mcp_server.entrypoint_controller

Configuration

You can customize the MCP Server Bundle configuration in config/packages/mcp_server.yaml:

mcp_server:
  server:
    name: 'My MCP Server' # The name of your MCP server, used in the initialization response
    title: 'My MCP Server Display Name' # The title of your MCP server, used in the initialization response
    version: '1.0.0' # The version of your MCP server, used in the initialization response

Tools

Tools are the core components of the MCP Server Bundle. They allow you to define and manage custom logic that can be triggered by clients.

Creating Tools

Create a new class that will handle your tool logic
Use the #[AsTool] attribute to register your tool
Define the input schema for your tool using a class with validation constraints and OpenAPI attributes
Implement the __invoke method to handle the tool logic and return a ToolResult

As Tool classes are services within the Symfony application, any dependency can be injected in it, using the constructor, like any other service.

Example:

Tool input schema class:

#[OA\Schema(required: ['emailAddress', 'username'])]
class CreateUserSchema
{
    #[Assert\Email]
    #[Assert\NotBlank]
    #[Assert\Length(min: 5, max: 255)]
    #[OA\Property(description: 'The email address of the user', type: 'string', maxLength: 255, minLength: 5, nullable: false)]
    public string $emailAddress;

    #[Assert\NotBlank]
    #[Assert\Length(min: 3, max: 50)]
    #[OA\Property(description: 'The username of the user', type: 'string', maxLength: 50, minLength: 3, nullable: false)]
    public string $username;
}

Tool class:

use App\Schema\CreateUserSchema;
use Ecourty\McpServerBundle\Attribute\AsTool;
use Ecourty\McpServerBundle\Attribute\ToolAnnotations;
use Ecourty\McpServerBundle\IO\TextToolResult;
use Ecourty\McpServerBundle\IO\ToolResult;

#[AsTool(
    name: 'create_user', # Unique identifier for the tool, used by clients to call it
    description: 'Creates a new user in the system', # This description is used by LLMs to understand the tool's purpose
    annotations: new ToolAnnotations(
        title: 'Create a user', // A human-readable title for the tool, useful for documentation
        readOnlyHint: false, // Defines the request is not read-only (creates a user)
        destructiveHint: false, // Defines the request is not destructive (does not delete data)
        idempotentHint: false, // Defines the request cannot be repeated without changing the state
        openWorldHint: false, // The tool does not interact with external systems
    )
)]
class CreateUserTool
{
    public function __invoke(CreateUserSchema $createUserSchema): ToolResult
    {
        // Your logic here...
        return new ToolResult([new TextToolResult('User created successfully!')]);
    }
}

Tool Results

The MCP specification states that tool results should consist of an array of objects.
The bundle provides several result types that can be combined in a single ToolResult object:

TextToolResult: For text-based results
ImageToolResult: For image results
AudioToolResult: For audio results
ResourceToolResult: For file or resource results

All tool results must be wrapped in a ToolResult object, which can contain multiple results and handle error state.

Example:

<?php

use App\Schema\ReadFileSchema;
use Ecourty\McpServerBundle\Attribute\AsTool;
use Ecourty\McpServerBundle\IO\TextToolResult;
use Ecourty\McpServerBundle\IO\ToolResult;

#[AsTool(name: 'read_file', description: 'Reads a file and returns its content')]
class MyTool
{
    public function __invoke(ReadFileSchema $payload): ToolResult
    {
        $fileContent = file_get_contents($payload->filePath);
        $anotherFileContent = file_get_contents($payload->anotherFilePath);

        // Create individual results
        $textResult = new TextToolResult($fileContent);
        $anotherTextResult = new TextToolResult($anotherFileContent);

        // Combine them in a ToolResult
        return new ToolResult([
            $textResult,
            $anotherTextResult,
        ]);
    }
}

Error handling example:

use Ecourty\McpServerBundle\IO\TextToolResult;
use Ecourty\McpServerBundle\IO\ToolResult;

class MyTool
{
    public function __invoke(): ToolResult
    {
        try {
            // Your logic here...
            return new ToolResult([
                new TextToolResult('Success!')
            ]);
        } catch (\Exception $e) {
            return new ToolResult(
                [new TextToolResult($e->getMessage())],
                isError: true
            );
        }
    }
}

The ToolResult class provides the following features:

Combine multiple results of different types
Handle error state
Automatic serialization to the correct format
Type safety for all results

Tool Events

The bundle provides several events that you can listen to:

ToolCallEvent: Dispatched before a tool is called, contains the tool name and input data
ToolResultEvent: Dispatched after a tool has been called, contains the result of the tool call
ToolCallExceptionEvent: Dispatched when a tool throws an exception, contains the tool name, input data and throwable

Example of event listener:

use Ecourty\McpServerBundle\Event\ToolCallEvent;
use Symfony\Component\EventDispatcher\Attribute\AsEventListener;

#[AsEventListener(event: ToolCallEvent::class)]
class ToolCallListener
{
    public function __invoke(ToolCallEvent $event): void
    {
        // Your logic here...
    }
}

Input Schema Management

The bundle provides robust input validation and sanitization through schema-based deserialization.
Input schemas are extracted from the __invoke method of classes with the #[AsTool] attribute, allowing you to define the expected input structure and validation rules.

Define your input schema class:

<?php

use OpenApi\Attributes as OA;
use Symfony\Component\Validator\Constraints as Assert;

class CreateUser
{
    #[Assert\NotBlank]
    #[Assert\Length(min: 2, max: 50)]
    #[OA\Property(type: 'string', description: 'The name of the user', nullable: false)]
    private string $name;

    #[Assert\NotBlank]
    #[Assert\Email]
    #[OA\Property(type: 'string', description: 'The email address of the user', nullable: false)]
    private string $email;

    // Getters and setters...
}

The bundle will automatically:
- Understand the OA attributes for OpenAPI-based documentation in tools/list
- Deserialize incoming JSON data into your schema class
- Validate all constraints defined in your schema
- Sanitize input data

This ensures that your tool handlers always receive properly validated and sanitized data.

JSON-RPC Integration

tools/list: Lists all available tools and their definitions.
tools/call: Executes a tool by name, with the provided input data.

Resources

Resources are data sources that can be accessed by clients via their URI.
They can represent files, database records, or any other data that can be identified by a URI.

Creating Resources

Create a new class that will handle your resource logic
Use the #[AsResource] attribute to register your resource
Define the URI pattern for your resource (static or templated)
Implement the __invoke method to handle the resource logic and return a ResourceResult

As Resource classes are services within the Symfony application, any dependency can be injected in it, using the constructor, like any other service.

Static Resources

Static resources have a fixed URI that doesn't change. They are useful for resources that don't require parameters.

Example:

<?php

use Ecourty\McpServerBundle\Attribute\AsResource;
use Ecourty\McpServerBundle\IO\Resource\ResourceResult;
use Ecourty\McpServerBundle\IO\Resource\TextResource;

#[AsResource(
    uri: 'file://robots.txt',
    name: 'robots_txt',
    title: 'Get the Robots.txt file',
    description: 'This resource returns the content of the robots.txt file.',
    mimeType: 'text/plain',
)]
class RobotsFileResource
{
    private const string FILE_PATH = __DIR__ . '/../Resources/robots.txt';

    public function __invoke(): ResourceResult
    {
        $fileContent = (string) file_get_contents(self::FILE_PATH);
        $encodedFileContent = base64_encode($fileContent);

        return new ResourceResult([
            new BinaryResource('file://robots.txt', 'text/plain', $encodedFileContent),
        ]);
    }
}

Templated Resources

Templated resources use URI templates with parameters enclosed in curly braces (e.g., {id}). These parameters are automatically extracted from the URI and passed to the __invoke method as arguments.

Example:

<?php

use Ecourty\McpServerBundle\Attribute\AsResource;
use Ecourty\McpServerBundle\IO\Resource\ResourceResult;
use Ecourty\McpServerBundle\IO\Resource\TextResource;

#[AsResource(
    uri: 'database://user/{id}',
    name: 'user_data',
    title: 'Get User Data',
    description: 'Gathers the data of a user by their ID.',
    mimeType: 'application/json',
)]
class UserResource
{
    public function __construct(
        private readonly EntityManagerInterface $entityManager,
        private readonly SerializerInterface $serializer,
    ) {
    }

    public function __invoke(int $id): ResourceResult
    {
        $user = $this->entityManager->find(User::class, $id);
        if ($user === null) {
            throw new \RuntimeException('User not found');
        }

        $stringifiedUserData = $this->serializer->serialize($user, 'json');

        return new ResourceResult([
            new TextResource(
                uri: 'database://user/' . $id,
                mimeType: 'application/json',
                text: $stringifiedUserData,
            ),
        ]);
    }
}

In this example:

The URI template database://user/{id} defines a parameter named id
When a client requests database://user/123, the parameter 123 is extracted
The __invoke method receives 123 as an int parameter (automatic type casting is performed)
The resource returns user data for ID 123

Multiple Parameters

You can define multiple parameters in a single URI template:

#[AsResource(
    uri: 'api://users/{userId}/posts/{postId}',
    name: 'user_post',
    title: 'Get User Post',
    description: 'Retrieves a specific post by a user.',
    mimeType: 'application/json',
)]
class UserPostResource
{
    public function __invoke(int $userId, int $postId): ResourceResult
    {
        // Your logic here...
        $post = $this->postRepository->findByUserAndPost($userId, $postId);
        
        return new ResourceResult([
            new TextResource(
                uri: "api://users/{$userId}/posts/{$postId}",
                mimeType: 'application/json',
                text: json_encode($post),
            ),
        ]);
    }
}

Parameter Type Casting

The bundle automatically casts URI parameters to the appropriate types based on the method signature:

int parameters are cast to integers
float parameters are cast to floats
bool parameters are cast to booleans
string parameters remain as strings
array parameters are JSON-decoded into arrays using json_decode if they are JSON strings

Resource Results

The MCP specification states that resource results should consist of an array of resource objects.
The bundle provides several result types that can be combined in a single ResourceResult object:

TextResource: For text-based content (JSON, XML, plain text, etc.)
BinaryResource: For binary content (images, audio, video, files, etc.), should be base-64 encoded

All resource results must be wrapped in a ResourceResult object, which can contain multiple resources.

Example:

<?php

use Ecourty\McpServerBundle\IO\Resource\ResourceResult;
use Ecourty\McpServerBundle\IO\Resource\TextResource;
use Ecourty\McpServerBundle\IO\Resource\BinaryResource;

#[AsResource(
    // ...
)]
class MyResource
{
    public function __invoke(): ResourceResult
    {
        $jsonData = json_encode(['status' => 'success']);
        $imageData = base64_encode(file_get_contents('image.jpg'));

        return new ResourceResult([
            new TextResource(
                uri: 'api://data/status',
                mimeType: 'application/json',
                text: $jsonData,
            ),
            new BinaryResource(
                uri: 'file://image.jpg',
                mimeType: 'image/jpeg',
                blob: $imageData,
            ),
        ]);
    }
}

The ResourceResult class provides the following features:

Combine multiple resources of different types
Automatic serialization to the correct format
Type safety for all resources

Resource Events

The bundle provides several events that you can listen to:

ResourceReadEvent: Dispatched before a resource is read, contains the URI
ResourceReadResultEvent: Dispatched after a resource has been read, contains the URI and results

Example of event listener:

<?php

use Ecourty\McpServerBundle\Event\ResourceReadEvent;
use Symfony\Component\EventDispatcher\Attribute\AsEventListener;

#[AsEventListener(event: ResourceReadEvent::class)]
class ResourceReadListener
{
    public function __invoke(ResourceReadEvent $event): void
    {
        // Your logic here...
        // Log the resource access, add caching, etc.
    }
}

JSON-RPC Integration

resources/list: Lists all available direct (static) resources and their definitions.
resources/templates/list: Lists all available templated resources and their definitions.
resources/read: Retrieves a resource by its URI, automatically matching templated resources and extracting parameters.

Prompts

Prompts are reusable templates that can be dynamically generated and returned by the MCP server.
They are useful for providing context, instructions, or any structured message to clients, and can accept arguments for dynamic content.

Creating Prompts

Define a prompt class
- Use the #[AsPrompt] attribute to register your prompt.
- The class should implement the __invoke method, which receives an ArgumentCollection and returns a PromptResult.
- Arguments are defined using the Argument class (name, description, required, allowUnsafe), within the #[AsPrompt] declaration.

Example:

<?php

namespace App\Prompt;

use Ecourty\McpServerBundle\Attribute\AsPrompt;
use Ecourty\McpServerBundle\Enum\PromptRole;
use Ecourty\McpServerBundle\IO\Prompt\Content\TextContent;
use Ecourty\McpServerBundle\Prompt\Argument;
use Ecourty\McpServerBundle\IO\Prompt\PromptResult;
use Ecourty\McpServerBundle\IO\Prompt\PromptMessage;
use Ecourty\McpServerBundle\Prompt\ArgumentCollection;

#[AsPrompt(
    name: 'code_review', // Unique identifier for the prompt,
    description: 'Ask for a code review on a provided piece of code', // Description of the prompt
    arguments: [
        new Argument(name: 'code', description: 'The code snippets to review', required: true, allowUnsafe: true), // Required argument
        new Argument(name: 'language', description: 'The name of the person to greet', required: false), // Optional argument
        new Argument(name: 'reviewer_level', description: 'The level of review (senior / intermediate / junior...)', required: false), // Optional argument
    ],
)]
class CodeReviewPrompt
{
    public function __invoke(ArgumentCollection $arguments): PromptResult
    {
        $code = $arguments->get('code');
        $language = $arguments->get('language');
        $reviewerLevel = $arguments->get('reviewer_level') ?: 'senior';

        $systemMessage = <<<PROMPT
You are a $reviewerLevel code reviewer.
You will be provided with a piece of code in $language.
Your task is to review the code and provide feedback on its quality, readability, and any potential issues.
PROMPT;

        $userMessage = <<<PROMPT
Review the following code snippet: $code
PROMPT;

        return new PromptResult(
            description: 'Code Review Prompt',
            messages: [
                new PromptMessage(
                    role: PromptRole::SYSTEM,
                    content: new TextContent($systemMessage),
                ),
                new PromptMessage(
                    role: PromptRole::USER,
                    content: new TextContent($userMessage),
                ),
            ]
        );
    }
}

Prompt Results

A prompt must return an instance of PromptResult, which contains:

A description (string)
An array of PromptMessage objects (each with a role and content)

Example:

return new PromptResult(
    description: 'Greeting',
    messages: [
        new PromptMessage(role: PromptRole::SYSTEM, content: new TextContent('You are a friendly assistant.')),
        new PromptMessage(role: PromptRole::USER, content: new TextContent('Hello, how are you?')),
    ]
);

Prompt Events

The bundle provides several events for prompts:

PromptGetEvent: Dispatched before a prompt is generated
PromptResultEvent: Dispatched after a prompt is generated
PromptExceptionEvent: Dispatched if an error occurs during prompt generation

Example of event listener:

use Ecourty\McpServerBundle\Event\Prompt\PromptExceptionEvent;
use Symfony\Component\EventDispatcher\Attribute\AsEventListener;

#[AsEventListener(event: PromptExceptionEvent::class)]
class PromptGetListener
{
    public function __invoke(PromptExceptionEvent $event): void
    {
        // Your logic here...
    }
}

JSON-RPC Integration

prompts/list: Lists all available prompts and their definitions.
prompts/get: Retrieves and generates a prompt by name, with arguments.

JSON-RPC Methods

The bundle provides a robust system for handling JSON-RPC requests.

Built-in Methods

initialize
- Called when a client first connects to the server
- Returns server information and capabilities
- Essential for client-server handshake
tools/list
- Lists all available tools on the server
- Returns tool metadata including names, descriptions, and input schemas
- Used by clients to discover available tools
tools/call
- Executes a specific tool
- Handles input validation and tool execution
- Returns the tool's result or error information
prompts/list
- Lists all available prompts and their definitions
- Returns prompt names, descriptions, and argument schemas
- Useful for clients to discover available prompts
prompts/get
- Retrieves a specific prompt by its name and generates it with the provided arguments
- Validates and sanitizes arguments, then returns the generated prompt content
- Returns an error if the prompt is not found or arguments are invalid
resources/list
- Lists all available static resources and their definitions
- Returns resource URIs, descriptions, and metadata
- Useful for clients to discover available resources
resources/templates/list
- Lists all available static and templated resources
- Returns resource URIs, descriptions, and metadata
- Useful for clients to discover available template resources
resources/read
- Reads a specific resource by its URI
- Automatically matches templated resources and extracts parameters
- Returns the resource content or an error if the resource is not found

These methods are automatically registered and handled by the bundle. You don't need to implement them yourself.

Custom Methods

You can create your own JSON-RPC method handlers for additional functionality:

Create a new class that implements the MethodHandlerInterface
Use the #[AsMethodHandler] attribute to register your handler

Example:

<?php

use Ecourty\McpServerBundle\Attribute\AsMethodHandler;
use Ecourty\McpServerBundle\MethodHandler\MethodHandlerInterface;

#[AsMethodHandler(
    method: 'my_method',
)]
class MyMethodHandler implements MethodHandlerInterface
{
    public function handle(JsonRpcRequest $params): array
    {
        // Your request handling logic here
        // ...

        return ['result' => 'success'];
    }
}

Method Handler Attributes

The #[AsMethodHandler] attribute supports:

method (string, required): The JSON-RPC method name

Developer Experience

The bundle provides several tools to help you during development:

Debug Command

The debug:mcp-tools command helps you inspect and debug your MCP tools:

# List all registered tools
php bin/console debug:mcp-tools

# Get detailed information about a specific tool
php bin/console debug:mcp-tools my_tool_name

This command is particularly useful for:

Verifying tool registration
Checking input schemas
Validating tool annotations

The debug:mcp-prompts command helps you inspect and debug your MCP prompts:

# List all registered prompts
php bin/console debug:mcp-prompts

# Get detailed information about a specific prompt
php bin/console debug:mcp-prompts my_prompt_name

This command is particularly useful for:

Verifying prompt registration
Checking argument

The debug:mcp-resources command helps you inspect and debug your MCP resources:

# List all registered resources
php bin/console debug:mcp-resources

# Get detailed information about a specific resource
php bin/console debug:mcp-resources my_resource_name

This command is particularly useful for:

Verifying resource registration
Checking URI patterns

Contributing

Contributions to the MCP Server Bundle are welcome! Here's how you can help:

Fork the repository
Create a new branch for your feature
Make your changes
Submit a pull request

Please ensure your code follows our coding standards and includes appropriate tests.

Development Setup

Fork and clone the repository
Install dependencies

composer install

Make your chages
Fix the code style and run PHPStan

composer fix-cs
composer phpstan

Run the tests

composer test

License

This bundle is licensed under the MIT License. See the LICENSE file for details.

mcp-server-bundle

MCP Server Bundle

Table of Contents

Getting Started

Installation

Configuration

Tools

Creating Tools

Tool Results

Tool Events

Input Schema Management

JSON-RPC Integration

Resources

Creating Resources

Static Resources

Templated Resources

Multiple Parameters

Parameter Type Casting

Resource Results

Resource Events

JSON-RPC Integration

Prompts

Creating Prompts

Prompt Results

Prompt Events

JSON-RPC Integration

JSON-RPC Methods

Built-in Methods

Custom Methods

Method Handler Attributes

Developer Experience

Debug Command

Contributing

Development Setup

License

Install

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