Add JSON Schema 2020-12 conformance test (SEP-1613) (#45)

Add conformance test to validate that MCP servers correctly preserve
JSON Schema 2020-12 keywords ($schema, $defs, additionalProperties)
in tool definitions.

Changes:
- Add JsonSchema2020_12Scenario in src/scenarios/server/json-schema-2020-12.ts
- Add json_schema_2020_12_tool to everything-server with tools/list override
  to return raw JSON Schema instead of Zod-converted schema
- Register scenario in pendingClientScenariosList (requires SDK PR #1135)

The test is added to pending because the client SDK currently strips
the JSON Schema 2020-12 keywords. Once PR #1135 is merged into the SDK,
this scenario can be moved to the active list.

examples/servers/typescript/everything-server.ts

@@ -13,7 +13,13 @@ import {
   ResourceTemplate
 } from '@modelcontextprotocol/sdk/server/mcp.js';
 import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
-import { ElicitResultSchema } from '@modelcontextprotocol/sdk/types.js';
+import {
+  ElicitResultSchema,
+  ListToolsRequestSchema,
+  type ListToolsResult,
+  type Tool
+} from '@modelcontextprotocol/sdk/types.js';
+import { zodToJsonSchema } from 'zod-to-json-schema';
 import { z } from 'zod';
 import express from 'express';
 import cors from 'cors';
@@ -35,6 +41,28 @@ const TEST_IMAGE_BASE64 =
 const TEST_AUDIO_BASE64 =
   'UklGRiYAAABXQVZFZm10IBAAAAABAAEAQB8AAAB9AAACABAAZGF0YQIAAAA=';
 
+// SEP-1613: Raw JSON Schema 2020-12 definition for conformance testing
+// This schema includes $schema, $defs, and additionalProperties to test
+// that SDKs correctly preserve these fields
+const JSON_SCHEMA_2020_12_INPUT_SCHEMA = {
+  $schema: 'https://json-schema.org/draft/2020-12/schema',
+  type: 'object' as const,
+  $defs: {
+    address: {
+      type: 'object',
+      properties: {
+        street: { type: 'string' },
+        city: { type: 'string' }
+      }
+    }
+  },
+  properties: {
+    name: { type: 'string' },
+    address: { $ref: '#/$defs/address' }
+  },
+  additionalProperties: false
+};
+
 // Function to create a new MCP server instance (one per session)
 function createMcpServer() {
   const mcpServer = new McpServer(
@@ -566,6 +594,40 @@ function createMcpServer() {
     }
   );
 
+  // SEP-1613: JSON Schema 2020-12 conformance test tool
+  // This tool is registered with a Zod schema for tools/call validation,
+  // but the tools/list handler (below) returns the raw JSON Schema 2020-12
+  // definition to test that SDKs preserve $schema, $defs, additionalProperties
+  mcpServer.registerTool(
+    'json_schema_2020_12_tool',
+    {
+      description:
+        'Tool with JSON Schema 2020-12 features for conformance testing (SEP-1613)',
+      inputSchema: {
+        name: z.string().optional(),
+        address: z
+          .object({
+            street: z.string().optional(),
+            city: z.string().optional()
+          })
+          .optional()
+      }
+    },
+    async (args: {
+      name?: string;
+      address?: { street?: string; city?: string };
+    }) => {
+      return {
+        content: [
+          {
+            type: 'text',
+            text: `JSON Schema 2020-12 tool called with: ${JSON.stringify(args)}`
+          }
+        ]
+      };
+    }
+  );
+
   // Dynamic tool (registered later via timer)
 
   // ===== RESOURCES =====
@@ -829,6 +891,80 @@ function createMcpServer() {
     }
   );
 
+  // ===== SEP-1613: Override tools/list to return raw JSON Schema 2020-12 =====
+  // This override is necessary because registerTool converts Zod schemas to
+  // JSON Schema without preserving $schema, $defs, and additionalProperties.
+  // We need to return the raw JSON Schema for our test tool while using the
+  // SDK's conversion for other tools.
+  mcpServer.server.setRequestHandler(
+    ListToolsRequestSchema,
+    (): ListToolsResult => {
+      // Access internal registered tools (this is internal SDK API but stable)
+      const registeredTools = (mcpServer as any)._registeredTools as Record<
+        string,
+        {
+          enabled: boolean;
+          title?: string;
+          description?: string;
+          inputSchema?: any;
+          outputSchema?: any;
+          annotations?: any;
+          _meta?: any;
+        }
+      >;
+
+      return {
+        tools: Object.entries(registeredTools)
+          .filter(([, tool]) => tool.enabled)
+          .map(([name, tool]): Tool => {
+            // For our SEP-1613 test tool, return raw JSON Schema 2020-12
+            if (name === 'json_schema_2020_12_tool') {
+              return {
+                name,
+                description: tool.description,
+                inputSchema: JSON_SCHEMA_2020_12_INPUT_SCHEMA
+              };
+            }
+
+            // For other tools, convert Zod to JSON Schema
+            // Handle different inputSchema formats:
+            // - undefined/null: use empty object schema
+            // - Zod schema (has _def): convert directly
+            // - Raw shape (object with Zod values): wrap in z.object first
+            let inputSchema: Tool['inputSchema'];
+            if (!tool.inputSchema) {
+              inputSchema = { type: 'object' as const, properties: {} };
+            } else if ('_def' in tool.inputSchema) {
+              // Already a Zod schema
+              inputSchema = zodToJsonSchema(tool.inputSchema, {
+                strictUnions: true
+              }) as Tool['inputSchema'];
+            } else if (
+              typeof tool.inputSchema === 'object' &&
+              Object.keys(tool.inputSchema).length > 0
+            ) {
+              // Raw shape with Zod values
+              inputSchema = zodToJsonSchema(z.object(tool.inputSchema), {
+                strictUnions: true
+              }) as Tool['inputSchema'];
+            } else {
+              // Empty object or unknown format
+              inputSchema = { type: 'object' as const, properties: {} };
+            }
+
+            return {
+              name,
+              title: tool.title,
+              description: tool.description,
+              inputSchema,
+              annotations: tool.annotations,
+              _meta: tool._meta
+            };
+          })
+      };
+    }
+  );
+
   return mcpServer;
 }