[Server] Add PropertyDescriberInterface extension point for SchemaGenerator

src/Capability/Discovery/PropertyDescriber/DateTimePropertyDescriber.php

@@ -0,0 +1,30 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Capability\Discovery\PropertyDescriber;
+
+use Mcp\Capability\Discovery\PropertyDescriberInterface;
+
+/**
+ * Describes any {@see \DateTimeInterface} implementation as an ISO-8601
+ * date-time string.
+ */
+final class DateTimePropertyDescriber implements PropertyDescriberInterface
+{
+    public function describe(string $className): ?array
+    {
+        if (!is_a($className, \DateTimeInterface::class, true)) {
+            return null;
+        }
+
+        return ['type' => 'string', 'format' => 'date-time'];
+    }
+}

src/Capability/Discovery/PropertyDescriber/UuidPropertyDescriber.php

@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Capability\Discovery\PropertyDescriber;
+
+use Mcp\Capability\Discovery\PropertyDescriberInterface;
+use Symfony\Component\Uid\Uuid;
+
+/**
+ * Describes Symfony UID {@see Uuid} (and subclasses like `UuidV4`, `UuidV7`)
+ * as a uuid-format string.
+ */
+final class UuidPropertyDescriber implements PropertyDescriberInterface
+{
+    public function describe(string $className): ?array
+    {
+        if (!is_a($className, Uuid::class, true)) {
+            return null;
+        }
+
+        return ['type' => 'string', 'format' => 'uuid'];
+    }
+}

src/Capability/Discovery/PropertyDescriberInterface.php

@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Capability\Discovery;
+
+/**
+ * Translates a PHP class type into a JSON Schema fragment.
+ *
+ * The {@see SchemaGenerator} consults registered describers, in order, before
+ * falling back to generic class inspection. The first describer that returns
+ * a non-null schema wins. Implementations let callers teach the generator
+ * about value-object types (DateTime, Uuid, etc.) whose JSON Schema
+ * representation is more specific than a generic `{type: "object"}`.
+ */
+interface PropertyDescriberInterface
+{
+    /**
+     * @param class-string $className
+     *
+     * @return array<string, mixed>|null Schema fragment, or null to pass to the next describer
+     */
+    public function describe(string $className): ?array;
+}

src/Capability/Discovery/SchemaGenerator.php

@@ -60,8 +60,14 @@
  */
 final class SchemaGenerator implements SchemaGeneratorInterface
 {
+    /**
+     * @param iterable<PropertyDescriberInterface> $propertyDescribers Consulted, in order, before
+     *                                                                 generic class inspection;
+     *                                                                 first non-null result wins
+     */
     public function __construct(
         private readonly DocBlockParser $docBlockParser,
+        private readonly iterable $propertyDescribers = [],
     ) {
     }
 
@@ -253,13 +259,22 @@ private function buildParameterSchema(array $paramInfo, ?array $methodLevelParam
      */
     private function buildInferredParameterSchema(array $paramInfo): array
     {
-        $paramSchema = [];
-
         // Variadic parameters are handled separately
         if ($paramInfo['is_variadic']) {
             return [];
         }
 
+        // Consult property describers for class-typed parameters first; the
+        // first describer that claims the class (returns non-null) wins. This
+        // lets callers teach the generator about value-object types like
+        // DateTime, Uuid, Money, etc. without subclassing the generator.
+        $describedSchema = $this->describeClassType($paramInfo);
+        if (null !== $describedSchema) {
+            return $this->applyParameterMetadata($describedSchema, $paramInfo);
+        }
+
+        $paramSchema = [];
+
         // Infer JSON Schema types
         $jsonTypes = $this->inferParameterTypes($paramInfo);
 
@@ -349,6 +364,65 @@ private function inferParameterTypes(array $paramInfo): array
         return $jsonTypes;
     }
 
+    /**
+     * Looks for a matching describer when the parameter's PHP type is a
+     * concrete class. Returns the first non-null describer result, or null
+     * if no describer claimed the type. Union and intersection types are
+     * not dispatched — describers see only single named, non-builtin types.
+     *
+     * @param ParameterInfo $paramInfo
+     *
+     * @return array<string, mixed>|null
+     */
+    private function describeClassType(array $paramInfo): ?array
+    {
+        $reflectionType = $paramInfo['reflection_type_object'];
+        if (!$reflectionType instanceof \ReflectionNamedType || $reflectionType->isBuiltin()) {
+            return null;
+        }
+
+        $className = $reflectionType->getName();
+        foreach ($this->propertyDescribers as $describer) {
+            $described = $describer->describe($className);
+            if (null !== $described) {
+                return $described;
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Layers parameter-level metadata (description, default, nullable) onto
+     * a describer-provided schema fragment without overwriting fields the
+     * describer already set.
+     *
+     * @param array<string, mixed> $schema
+     * @param ParameterInfo        $paramInfo
+     *
+     * @return array<string, mixed>
+     */
+    private function applyParameterMetadata(array $schema, array $paramInfo): array
+    {
+        if ($paramInfo['description'] && !isset($schema['description'])) {
+            $schema['description'] = $paramInfo['description'];
+        }
+
+        if ($paramInfo['has_default'] && !isset($schema['default'])) {
+            $schema['default'] = $paramInfo['default_value'];
+        }
+
+        if ($paramInfo['allows_null'] && isset($schema['type'])) {
+            $types = \is_array($schema['type']) ? $schema['type'] : [$schema['type']];
+            if (!\in_array('null', $types, true)) {
+                array_unshift($types, 'null');
+            }
+            $schema['type'] = 1 === \count($types) ? $types[0] : $types;
+        }
+
+        return $schema;
+    }
+
     /**
      * Applies enum constraints to parameter schema.
      */

tests/Unit/Capability/Discovery/PropertyDescriber/DateTimePropertyDescriberTest.php

@@ -0,0 +1,51 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Unit\Capability\Discovery\PropertyDescriber;
+
+use Mcp\Capability\Discovery\PropertyDescriber\DateTimePropertyDescriber;
+use PHPUnit\Framework\TestCase;
+
+final class DateTimePropertyDescriberTest extends TestCase
+{
+    private DateTimePropertyDescriber $describer;
+
+    protected function setUp(): void
+    {
+        $this->describer = new DateTimePropertyDescriber();
+    }
+
+    public function testDescribesDateTimeInterfaceAsIsoDateTimeString(): void
+    {
+        $this->assertSame(
+            ['type' => 'string', 'format' => 'date-time'],
+            $this->describer->describe(\DateTimeInterface::class),
+        );
+    }
+
+    public function testDescribesDateTimeImplementations(): void
+    {
+        $this->assertSame(
+            ['type' => 'string', 'format' => 'date-time'],
+            $this->describer->describe(\DateTime::class),
+        );
+        $this->assertSame(
+            ['type' => 'string', 'format' => 'date-time'],
+            $this->describer->describe(\DateTimeImmutable::class),
+        );
+    }
+
+    public function testPassesOnUnrelatedClass(): void
+    {
+        $this->assertNull($this->describer->describe(\stdClass::class));
+        $this->assertNull($this->describer->describe(\Exception::class));
+    }
+}

tests/Unit/Capability/Discovery/PropertyDescriber/UuidPropertyDescriberTest.php

@@ -0,0 +1,54 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Unit\Capability\Discovery\PropertyDescriber;
+
+use Mcp\Capability\Discovery\PropertyDescriber\UuidPropertyDescriber;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Uid\Uuid;
+use Symfony\Component\Uid\UuidV4;
+use Symfony\Component\Uid\UuidV6;
+
+final class UuidPropertyDescriberTest extends TestCase
+{
+    private UuidPropertyDescriber $describer;
+
+    protected function setUp(): void
+    {
+        $this->describer = new UuidPropertyDescriber();
+    }
+
+    public function testDescribesUuidAsUuidFormatString(): void
+    {
+        $this->assertSame(
+            ['type' => 'string', 'format' => 'uuid'],
+            $this->describer->describe(Uuid::class),
+        );
+    }
+
+    public function testDescribesUuidSubclasses(): void
+    {
+        $this->assertSame(
+            ['type' => 'string', 'format' => 'uuid'],
+            $this->describer->describe(UuidV4::class),
+        );
+        $this->assertSame(
+            ['type' => 'string', 'format' => 'uuid'],
+            $this->describer->describe(UuidV6::class),
+        );
+    }
+
+    public function testPassesOnUnrelatedClass(): void
+    {
+        $this->assertNull($this->describer->describe(\stdClass::class));
+        $this->assertNull($this->describer->describe(\DateTime::class));
+    }
+}

tests/Unit/Capability/Discovery/SchemaGeneratorFixture.php

@@ -438,6 +438,37 @@ public function withParameterNamedRequest(string $_request): void
     {
     }
 
+    // ===== PROPERTY DESCRIBER FIXTURES =====
+
+    public function dateTimeParam(\DateTimeImmutable $createdAt): void
+    {
+    }
+
+    /**
+     * @param \DateTimeInterface $until The cutoff timestamp
+     */
+    public function dateTimeWithDescription(\DateTimeInterface $until): void
+    {
+    }
+
+    public function nullableDateTimeParam(?\DateTimeImmutable $finishedAt = null): void
+    {
+    }
+
+    public function uuidParam(\Symfony\Component\Uid\Uuid $bookingId): void
+    {
+    }
+
+    public function unrelatedObjectParam(\stdClass $config): void
+    {
+    }
+
+    public function dateTimeWithSchemaAttributeOverride(
+        #[Schema(description: 'explicit attribute description')]
+        \DateTimeImmutable $deadline,
+    ): void {
+    }
+
     // ===== OUTPUT SCHEMA FIXTURES =====
     #[McpTool(
         outputSchema: [