[Server] Describe tool inputs and outputs with their direction

Input schemas only list the properties a client can send (Direction::Input), and output schemas require the properties that are always present (Direction::Output). A dialect without schema URI makes stripping $schema unnecessary, and definitions keep the plain class name since each schema is a document of its own.

Author: nicolas-grekas

CHANGELOG.md

@@ -9,7 +9,7 @@ All notable changes to `mcp/sdk` will be documented in this file.
 
 * Discovery
   * [BC Break] Generate tool input and output schemas with `symfony/json-schema`. Unions are described with `anyOf`, `null` comes last in `type`, `default: null` is no longer emitted, array shapes are closed with `additionalProperties: false`, string-keyed maps get `additionalProperties`, and a class parameter is described by its properties.
-  * [BC Break] `SchemaGenerator` takes a `Symfony\Component\JsonSchema\SchemaGeneratorInterface`, a `TypeResolverInterface` and a `Configuration` instead of a `DocBlockParser`.
+  * [BC Break] `SchemaGenerator` takes a `Symfony\Component\JsonSchema\SchemaGeneratorInterface`, a `TypeResolverInterface` and the input and output `Configuration` instead of a `DocBlockParser`.
   * [BC Break] Remove `DocBlockParser::getParamTypeString()` and `DocBlockParser::getParamDescription()`.
   * Add the `outputSchemaFromReturnType` argument of `SchemaGenerator`, to describe the output of a tool that returns an object by its class.
 

src/Server/Capability/Discovery/SchemaGenerator.php

@@ -17,6 +17,9 @@
 use Mcp\Server\Exception\BadMethodCallException;
 use Mcp\Server\Exception\InvalidArgumentException;
 use Symfony\Component\JsonSchema\Configuration;
+use Symfony\Component\JsonSchema\Dialect;
+use Symfony\Component\JsonSchema\Direction;
+use Symfony\Component\JsonSchema\NullSyntax;
 use Symfony\Component\JsonSchema\Schema as JsonSchema;
 use Symfony\Component\JsonSchema\SchemaGenerator as JsonSchemaGenerator;
 use Symfony\Component\JsonSchema\SchemaGeneratorInterface as JsonSchemaGeneratorInterface;
@@ -35,11 +38,18 @@ final class SchemaGenerator implements SchemaGeneratorInterface
     private readonly JsonSchemaGeneratorInterface $generator;
     private readonly TypeResolverInterface $typeResolver;
 
+    /**
+     * Each schema is a document of its own, so definitions are named after their class only.
+     *
+     * @param Configuration $configuration       The configuration of input schemas
+     * @param Configuration $outputConfiguration The configuration of output schemas
+     */
     public function __construct(
         ?JsonSchemaGeneratorInterface $generator = null,
         ?TypeResolverInterface $typeResolver = null,
-        private readonly Configuration $configuration = new Configuration(),
+        private readonly Configuration $configuration = new Configuration(new Dialect('#/$defs/', NullSyntax::Union), definitionName: '', direction: Direction::Input),
         private readonly bool $outputSchemaFromReturnType = false,
+        private readonly Configuration $outputConfiguration = new Configuration(new Dialect('#/$defs/', NullSyntax::Union), definitionName: '', direction: Direction::Output),
     ) {
         $this->generator = $generator ?? JsonSchemaGenerator::create();
         $this->typeResolver = $typeResolver ?? TypeResolver::create();
@@ -72,7 +82,6 @@ public function generate(\Reflector $reflection): array
         }
 
         $schema = self::toArray($this->generator->generateForParameters(array_values($parameters), $this->configuration)->flatten());
-        unset($schema['$schema']);
 
         $methodProperties = $methodSchema['properties'] ?? [];
         $methodRequired = $methodSchema['required'] ?? [];
@@ -129,8 +138,7 @@ public function generateOutputSchema(\Reflector $reflection): ?array
             return null;
         }
 
-        $schema = self::toArray($this->generator->generate($type, $this->configuration)->flatten());
-        unset($schema['$schema']);
+        $schema = self::toArray($this->generator->generate($type, $this->outputConfiguration)->flatten());
 
         return $schema;
     }

tests/Unit/Server/Capability/Discovery/SchemaGeneratorTest.php

@@ -790,7 +790,7 @@ public function testOutputSchemaFromReturnTypeIsOptIn(): void
         $schema = (new SchemaGenerator(outputSchemaFromReturnType: true))->generateOutputSchema($method);
         $this->assertNotNull($schema);
         $this->assertSame('object', $schema['type']);
-        $this->assertSame(['email', 'age'], $schema['required']);
+        $this->assertSame(['email', 'age', 'address', 'tags', 'birthday'], $schema['required']);
     }
 
     public function testExplicitOutputSchemaWins(): void