Add OpenAPI extensions support to HTTPRoute

- Add extensions field to HTTPRoute class to store x-* fields
- Extract extensions from operation's model_extra in parser
- Add test to verify extensions are properly parsed

src/fastmcp/utilities/openapi.py

@@ -84,6 +84,7 @@ class HTTPRoute(FastMCPBaseModel):
     schema_definitions: dict[str, JsonSchema] = Field(
         default_factory=dict
     )  # Store component schemas
+    extensions: dict[str, Any] = Field(default_factory=dict)
 
 
 # Export public symbols
@@ -591,6 +592,14 @@ class OpenAPIParser(
                             getattr(operation, "responses", None)
                         )
 
+                        extensions = {}
+                        if hasattr(operation, "model_extra") and operation.model_extra:
+                            extensions = {
+                                k: v
+                                for k, v in operation.model_extra.items()
+                                if k.startswith("x-")
+                            }
+
                         route = HTTPRoute(
                             path=path_str,
                             method=method_upper,  # type: ignore[arg-type]  # Known valid HTTP method
@@ -602,6 +611,7 @@ class OpenAPIParser(
                             request_body=request_body_info,
                             responses=responses,
                             schema_definitions=schema_definitions,
+                            extensions=extensions,
                         )
                         routes.append(route)
                         logger.info(

tests/utilities/openapi/test_openapi.py

@@ -687,6 +687,29 @@ def test_multiple_tags_preserved(bookstore_schema):
     assert len(get_books.tags) == 3
 
 
+def test_openapi_extensions(petstore_schema):
+    """Test that OpenAPI extensions (x-*) are correctly parsed from operations."""
+    # Add extensions to a route
+    petstore_schema["paths"]["/pets"]["get"]["x-rate-limit"] = 100
+    petstore_schema["paths"]["/pets"]["get"]["x-custom-auth"] = "bearer"
+    petstore_schema["paths"]["/pets"]["get"]["x-internal"] = True
+
+    # Parse the modified schema
+    routes = parse_openapi_to_http_routes(petstore_schema)
+
+    # Find the GET /pets route
+    get_pets = next(
+        (r for r in routes if r.method == "GET" and r.path == "/pets"), None
+    )
+    assert get_pets is not None
+
+    # Should have extensions
+    assert get_pets.extensions["x-rate-limit"] == 100
+    assert get_pets.extensions["x-custom-auth"] == "bearer"
+    assert get_pets.extensions["x-internal"] is True
+    assert len(get_pets.extensions) == 3
+
+
 # --- Tests for BookStore schema --- #