Add configurable JSON Schema target specification for OpenAI

README.md

@@ -117,6 +117,27 @@ const server = new McpServer({
 });
 ```
 
+#### JSON Schema Specification
+
+You can configure the JSON Schema target specification for better compatibility with different systems, particularly OpenAI endpoints:
+
+```typescript
+const server = new McpServer({
+  name: "my-app",
+  version: "1.0.0"
+}, {
+  jsonSchemaSpec: 'openApi3'  // For OpenAI compatibility
+});
+```
+
+Supported values include:
+- `'jsonSchema7'` (default) - JSON Schema Draft 7
+- `'openApi3'` - OpenAPI 3.0 specification (recommended for OpenAI compatibility)
+- `'jsonSchema4'` - JSON Schema Draft 4
+- `'jsonSchema2019-09'` - JSON Schema Draft 2019-09
+
+This setting affects how tool input schemas are generated from Zod schemas, ensuring they match the expected format for your target system.
+
 ### Resources
 
 Resources are how you expose data to LLMs. They're similar to GET endpoints in a REST API - they provide data but shouldn't perform significant computation or have side effects:

src/server/index.ts

@@ -37,6 +37,7 @@ import {
   LoggingLevelSchema
 } from "../types.js";
 import Ajv from "ajv";
+import type { Targets } from "zod-to-json-schema";
 
 export type ServerOptions = ProtocolOptions & {
   /**
@@ -48,6 +49,11 @@ export type ServerOptions = ProtocolOptions & {
    * Optional instructions describing how to use the server and its features.
    */
   instructions?: string;
+
+  /**
+   * Optional spec for JSON Schema to allow fully compatible use with OpenAI endpoints.
+   */
+  jsonSchemaSpec?: Targets;
 };
 
 /**
@@ -88,6 +94,7 @@ export class Server<
   private _clientVersion?: Implementation;
   private _capabilities: ServerCapabilities;
   private _instructions?: string;
+  public _jsonSchemaSpec?: Targets = 'jsonSchema7';
 
   /**
    * Callback for when initialization has fully completed (i.e., the client has sent an `initialized` notification).
@@ -104,6 +111,7 @@ export class Server<
     super(options);
     this._capabilities = options?.capabilities ?? {};
     this._instructions = options?.instructions;
+    this._jsonSchemaSpec = options?.jsonSchemaSpec;
 
     this.setRequestHandler(InitializeRequestSchema, (request) =>
       this._oninitialize(request),

src/server/mcp.ts

@@ -119,6 +119,7 @@ export class McpServer {
               description: tool.description,
               inputSchema: tool.inputSchema
                 ? (zodToJsonSchema(tool.inputSchema, {
+                  target: this.server._jsonSchemaSpec,
                   strictUnions: true,
                 }) as Tool["inputSchema"])
                 : EMPTY_OBJECT_JSON_SCHEMA,