Add possibility to set custom ServerCapabilities. (#95)

Author: ineersa

examples/stdio-explicit-registration/server.php

@@ -14,6 +14,7 @@
 chdir(__DIR__);
 
 use Mcp\Example\StdioExplicitRegistration\SimpleHandlers;
+use Mcp\Schema\ServerCapabilities;
 use Mcp\Server;
 use Mcp\Server\Transport\StdioTransport;
 
@@ -27,6 +28,17 @@
     ->addResource([SimpleHandlers::class, 'getAppVersion'], 'app://version', 'application_version', mimeType: 'text/plain')
     ->addPrompt([SimpleHandlers::class, 'greetingPrompt'], 'personalized_greeting')
     ->addResourceTemplate([SimpleHandlers::class, 'getItemDetails'], 'item://{itemId}/details', 'get_item_details', mimeType: 'application/json')
+    ->setServerCapabilities(new ServerCapabilities(
+        tools: true,
+        toolsListChanged: false,
+        resources: true,
+        resourcesSubscribe: false,
+        resourcesListChanged: false,
+        prompts: true,
+        promptsListChanged: false,
+        logging: false,
+        completions: false,
+    ))
     ->build();
 
 $transport = new StdioTransport(logger: logger());

src/Capability/Registry.php

@@ -63,6 +63,8 @@ final class Registry implements ReferenceProviderInterface, ReferenceRegistryInt
      */
     private array $resourceTemplates = [];
 
+    private ServerCapabilities $serverCapabilities;
+
     public function __construct(
         private readonly ?EventDispatcherInterface $eventDispatcher = null,
         private readonly LoggerInterface $logger = new NullLogger(),
@@ -75,7 +77,7 @@ public function getCapabilities(): ServerCapabilities
             $this->logger->info('No capabilities registered on server.');
         }
 
-        return new ServerCapabilities(
+        return $this->serverCapabilities ?? new ServerCapabilities(
             tools: [] !== $this->tools,
             toolsListChanged: $this->eventDispatcher instanceof EventDispatcherInterface,
             resources: [] !== $this->resources || [] !== $this->resourceTemplates,
@@ -453,4 +455,9 @@ private function paginateResults(array $items, int $limit, ?string $cursor = nul
 
         return array_values(\array_slice($items, $offset, $limit));
     }
+
+    public function setServerCapabilities(ServerCapabilities $serverCapabilities): void
+    {
+        $this->serverCapabilities = $serverCapabilities;
+    }
 }

src/Server/Builder.php

@@ -138,6 +138,8 @@ final class Builder
      */
     private array $discoveryExcludeDirs = [];
 
+    private ?ServerCapabilities $serverCapabilities = null;
+
     /**
      * Sets the server's identity. Required.
      */
@@ -264,6 +266,13 @@ public function setDiscovery(
         return $this;
     }
 
+    public function setServerCapabilities(ServerCapabilities $serverCapabilities): self
+    {
+        $this->serverCapabilities = $serverCapabilities;
+
+        return $this;
+    }
+
     /**
      * Manually registers a tool handler.
      *
@@ -348,6 +357,9 @@ public function build(): Server
         $registry = new Registry($this->eventDispatcher, $logger);
 
         $this->registerCapabilities($registry, $logger);
+        if ($this->serverCapabilities) {
+            $registry->setServerCapabilities($this->serverCapabilities);
+        }
 
         if (null !== $this->discoveryBasePath) {
             $this->performDiscovery($registry, $logger);

tests/Unit/Capability/Registry/RegistryTest.php

@@ -80,6 +80,42 @@ public function testGetCapabilitiesWhenPopulated(): void
         $this->assertFalse($capabilities->logging);
     }
 
+    public function testSetCustomCapabilities(): void
+    {
+        $serverCapabilities = new ServerCapabilities(
+            tools: false,
+            toolsListChanged: true,
+            resources: false,
+            resourcesSubscribe: false,
+            resourcesListChanged: false,
+            prompts: false,
+            promptsListChanged: false,
+            logging: true,
+            completions: true,
+        );
+        $tool = $this->createValidTool('test_tool');
+        $resource = $this->createValidResource('test://resource');
+        $prompt = $this->createValidPrompt('test_prompt');
+        $template = $this->createValidResourceTemplate('test://{id}');
+
+        $this->registry->registerTool($tool, fn () => 'result');
+        $this->registry->registerResource($resource, fn () => 'content');
+        $this->registry->registerPrompt($prompt, fn () => []);
+        $this->registry->registerResourceTemplate($template, fn () => 'template');
+
+        $this->registry->setServerCapabilities($serverCapabilities);
+
+        $capabilities = $this->registry->getCapabilities();
+
+        $this->assertFalse($capabilities->tools);
+        $this->assertFalse($capabilities->resources);
+        $this->assertFalse($capabilities->prompts);
+        $this->assertTrue($capabilities->completions);
+        $this->assertFalse($capabilities->resourcesSubscribe);
+        $this->assertTrue($capabilities->logging);
+        $this->assertTrue($capabilities->toolsListChanged);
+    }
+
     public function testRegisterToolWithManualFlag(): void
     {
         $tool = $this->createValidTool('test_tool');