docs: Add documentation for jsonSchemaSpec configuration option

- Add section explaining jsonSchemaSpec option in Server documentation
- Document supported values (jsonSchema7, openApi3, etc.)
- Explain use case for OpenAI compatibility
- Provide usage examples

Author: ashburnham

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: