[MCP SDK] Add server capabilities toSymfony\AI\McpSdk\Server\RequestHandler\InitializeHandler

src/mcp-sdk/doc/index.rst

@@ -56,8 +56,17 @@ Capabilities
 
 Any client would like to discover the capabilities of the server. Exactly what
 the server supports is defined in the ``Symfony\AI\McpSdk\Server\RequestHandler\InitializeHandler``.
-When the client connects, it sees the capabilities and will ask the server to list
-the tools/resource/prompts etc. When you want to add a new capability, example a
+When the client connects, it sends an ``initialize`` request. The server responds
+with its capabilities, which are defined by two main classes:
+
+* ``Symfony\AI\McpSdk\Capability\Server\Implementation``: Describes the server software itself (e.g., its name and version).
+* ``Symfony\AI\McpSdk\Capability\Server\ServerCapabilities``: Details the features the server supports, such as tools, prompts, or resources.
+
+After that client see available capabilities and will ask the server to list the tools/resource/prompts etc. depending on ``ServerCapabilities`` you provided.
+Also ``initialize`` request provides information about protocol version, instructions and ``_meta`` field.
+You can find more information about ``Initialize`` response `InitializeResult <https://modelcontextprotocol.io/specification/2025-06-18/schema#initializeresult>`_
+
+When you want to add a new tool for example:
 **Tool** that can tell the current time, you need to provide some metadata to the
 ``Symfony\AI\McpSdk\Server\RequestHandler\ToolListHandler``::
 

src/mcp-sdk/examples/cli/src/Builder.php

@@ -11,8 +11,14 @@
 
 namespace App;
 
+use Symfony\AI\McpSdk\Capability\Prompt\PromptCapability;
 use Symfony\AI\McpSdk\Capability\PromptChain;
+use Symfony\AI\McpSdk\Capability\Resource\ResourceCapability;
 use Symfony\AI\McpSdk\Capability\ResourceChain;
+use Symfony\AI\McpSdk\Capability\Server\Implementation;
+use Symfony\AI\McpSdk\Capability\Server\ProtocolVersion;
+use Symfony\AI\McpSdk\Capability\Server\ServerCapabilities;
+use Symfony\AI\McpSdk\Capability\Tool\ToolCapability;
 use Symfony\AI\McpSdk\Capability\ToolChain;
 use Symfony\AI\McpSdk\Server\NotificationHandler\InitializedHandler;
 use Symfony\AI\McpSdk\Server\NotificationHandlerInterface;
@@ -45,8 +51,23 @@ public static function buildRequestHandlers(): array
             new ExampleTool(),
         ]);
 
+        $implementation = new Implementation(
+            name: 'MCP-SDK-CLI-Example',
+            version: '0.1.0'
+        );
+        $serverCapabilities = new ServerCapabilities(
+            prompts: new PromptCapability(listChanged: false),
+            resources: new ResourceCapability(subscribe: false, listChanged: false),
+            tools: new ToolCapability(listChanged: false),
+        );
+
         return [
-            new InitializeHandler(),
+            new InitializeHandler(
+                implementation: $implementation,
+                serverCapabilities: $serverCapabilities,
+                protocolVersion: ProtocolVersion::V2025_03_26,
+                instructions: 'Optional LLM instructions/hints',
+            ),
             new PingHandler(),
             new PromptListHandler($promptManager),
             new PromptGetHandler($promptManager),

src/mcp-sdk/src/Capability/Completion/CompletionCapability.php

@@ -0,0 +1,24 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Completion;
+
+/**
+ * Present if the server supports argument autocompletion suggestions.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-completions
+ */
+final class CompletionCapability
+{
+    public function __construct(
+    ) {
+    }
+}

src/mcp-sdk/src/Capability/Logging/LoggingCapability.php

@@ -0,0 +1,24 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Logging;
+
+/**
+ * Present if the server supports sending log messages to the client.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-logging
+ */
+final class LoggingCapability
+{
+    public function __construct(
+    ) {
+    }
+}

src/mcp-sdk/src/Capability/Prompt/PromptCapability.php

@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Prompt;
+
+/**
+ * Present if the server offers any prompt templates.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-logging
+ */
+final readonly class PromptCapability
+{
+    public function __construct(
+        /** Whether this server supports notifications for changes to the prompt list. */
+        public ?bool $listChanged = null,
+    ) {
+    }
+}

src/mcp-sdk/src/Capability/Resource/ResourceCapability.php

@@ -0,0 +1,28 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Resource;
+
+/**
+ * Present if the server offers any resources to read.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-resources
+ */
+final readonly class ResourceCapability
+{
+    public function __construct(
+        /** Whether this server supports notifications for changes to the resource list. */
+        public ?bool $subscribe = null,
+        /** Whether this server supports subscribing to resource updates. */
+        public ?bool $listChanged = null,
+    ) {
+    }
+}

src/mcp-sdk/src/Capability/Server/Implementation.php

@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Server;
+
+/**
+ * Describes the name and version of an MCP implementation, with an optional title for UI representation.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#implementation
+ */
+final readonly class Implementation
+{
+    public function __construct(
+        public string $name = 'app',
+        public string $version = 'dev',
+    ) {
+    }
+}

src/mcp-sdk/src/Capability/Server/ProtocolVersion.php

@@ -0,0 +1,19 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Server;
+
+enum ProtocolVersion: string
+{
+    case V2024_11_05 = '2024-11-05';
+    case V2025_03_26 = '2025-03-26';
+    case V2025_06_18 = '2025-06-18';
+}

src/mcp-sdk/src/Capability/Server/ServerCapabilities.php

@@ -0,0 +1,83 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Server;
+
+use Symfony\AI\McpSdk\Capability\Completion\CompletionCapability;
+use Symfony\AI\McpSdk\Capability\Logging\LoggingCapability;
+use Symfony\AI\McpSdk\Capability\Prompt\PromptCapability;
+use Symfony\AI\McpSdk\Capability\Resource\ResourceCapability;
+use Symfony\AI\McpSdk\Capability\Tool\ToolCapability;
+
+/**
+ * Capabilities that a server may support. Known capabilities are defined here, in this schema,
+ * but this is not a closed set: any server can define its own, additional capabilities.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities
+ */
+final readonly class ServerCapabilities implements \JsonSerializable
+{
+    /**
+     * @param array<string, array<string, mixed>>|null $experimental
+     */
+    public function __construct(
+        /**
+         * Present if the server supports sending log messages to the client.
+         *
+         * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-logging
+         */
+        public ?LoggingCapability $logging = null,
+        /**
+         * Present if the server offers any prompt templates.
+         *
+         * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-prompts
+         */
+        public ?PromptCapability $prompts = null,
+        /**
+         * Present if the server offers any resources to read.
+         *
+         * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-resources
+         */
+        public ?ResourceCapability $resources = null,
+        /**
+         * Present if the server offers any tools to call.
+         *
+         * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-tools
+         */
+        public ?ToolCapability $tools = null,
+        /**
+         * Present if the server supports argument autocompletion suggestions.
+         *
+         * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-completions
+         */
+        public ?CompletionCapability $completions = null,
+        /**
+         * @var array<string, array<string, mixed>>|null
+         */
+        public ?array $experimental = null,
+    ) {
+    }
+
+    /**
+     * @return array{
+     *     logging?: LoggingCapability,
+     *     prompts?: PromptCapability,
+     *     resources?: ResourceCapability,
+     *     tools?: ToolCapability,
+     *     completions?: CompletionCapability,
+     *     experimental?: array<string, array<string, mixed>>
+     * }
+     */
+    public function jsonSerialize(): array
+    {
+        return array_filter((array) $this, fn ($value) => null !== $value);
+    }
+}

src/mcp-sdk/src/Capability/Tool/ToolCapability.php

@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Capability\Tool;
+
+/**
+ * Present if the server offers any tools to call.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/schema#servercapabilities-tools
+ */
+final readonly class ToolCapability
+{
+    public function __construct(
+        /** Whether this server supports notifications for changes to the tool list. */
+        public ?bool $listChanged = null,
+    ) {
+    }
+}

src/mcp-sdk/src/Field/MetaField.php

@@ -0,0 +1,38 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\AI\McpSdk\Field;
+
+/**
+ * The _meta property/parameter is reserved by MCP to allow clients and servers to attach additional metadata to their interactions. Certain key names are reserved by MCP for protocol-level metadata, as specified below; implementations MUST NOT make assumptions about values at these keys. Additionally, definitions in the schema may reserve particular names for purpose-specific metadata, as declared in those definitions. Key name format: valid _meta key names have two segments: an optional prefix, and a name. Prefix:
+ *
+ * If specified, MUST be a series of labels separated by dots (.), followed by a slash (/).
+ * Labels MUST start with a letter and end with a letter or digit; interior characters can be letters, digits, or hyphens (-).
+ * Any prefix beginning with zero or more valid labels, followed by modelcontextprotocol or mcp, followed by any valid label, is reserved for MCP use.
+ * For example: modelcontextprotocol.io/, mcp.dev/, api.modelcontextprotocol.org/, and tools.mcp.com/ are all reserved.
+ *
+ * Name:
+ *
+ * Unless empty, MUST begin and end with an alphanumeric character ([a-z0-9A-Z]).
+ * MAY contain hyphens (-), underscores (_), dots (.), and alphanumerics in between.
+ *
+ * @see https://modelcontextprotocol.io/specification/2025-06-18/basic/index#general-fields
+ */
+final readonly class MetaField
+{
+    /**
+     * @param array<string, mixed> $meta
+     */
+    public function __construct(
+        public array $meta,
+    ) {
+    }
+}

src/mcp-sdk/src/Message/Notification.php

@@ -22,6 +22,11 @@ public function __construct(
     ) {
     }
 
+    public function __toString(): string
+    {
+        return \sprintf('%s', $this->method);
+    }
+
     /**
      * @param array{method: string, params?: array<string, mixed>} $data
      */
@@ -44,9 +49,4 @@ public function jsonSerialize(): array
             'params' => $this->params,
         ];
     }
-
-    public function __toString(): string
-    {
-        return \sprintf('%s', $this->method);
-    }
 }