Is openapi 3.0.x supported actually ?

[thedevd]

Hi @jlowin , Is openapi 3.0.x really supported with fastmcp 2.11.x version. As I just tried openapi 3.0.x api specification and I am still seeing input schema validation error.

Error- when calling tool
Input validation error: None is not of type 'string'

Schema example I am trying - (Note - I have verified my openapi 3.0.x schema using swagger online editor, and there things are ok)

{
  "openapi": "3.0.0",
  "info": {
      "title": "UAC",
      "description": "Manage users, roles etc",
      "version": "1"
  },
  "paths": {
  .....
  .....
   "/api/v1/users": {
          "get": {
              "operationId": "v1_users_list",
              "responses": {
                  "200": {
                      "description": "OK",
                      "content": {
                          "*/*": {
                              "schema": {
                                  "$ref": "#/components/schemas/UserSerializer"
                              }
                          }
                      }
                  },
                  "400": {
                      "description": "Bad Request"
                  },
                  "401": {
                      "description": "Authentication credentials were not provided"
                  },
                  "403": {
                      "description": "Forbidden"
                  }
              },
              "parameters": [
                  {
                      "name": "uuid",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "role",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "usergroup",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "tenant",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "current_logged_in",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "is_active",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "is_internal",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "is_locked",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "is_staff",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "email",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "email__startswith",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "email__contains",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "first_name",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "first_name__startswith",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "first_name__contains",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "last_name",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "last_name__startswith",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "last_name__contains",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "username",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "username__startswith",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "username__contains",
                      "required": false,
                      "in": "query",
                      "description": "",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "search",
                      "required": false,
                      "in": "query",
                      "description": "A search term.",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "ordering",
                      "required": false,
                      "in": "query",
                      "description": "Which field to use when ordering the results.",
                      "schema": {
                          "type": "string"
                      }
                  },
                  {
                      "name": "page",
                      "required": false,
                      "in": "query",
                      "description": "A page number within the paginated result set.",
                      "schema": {
                          "type": "integer"
                      }
                  },
                  {
                      "name": "limit",
                      "required": false,
                      "in": "query",
                      "description": "Number of results to return per page.",
                      "schema": {
                          "type": "integer"
                      }
                  }
              ],
              "description": "List of users.\n\nCustom Filter current_logged_in can be used to get currently logged in users,\nGET api/v1/users?current_logged_in=True",
              "summary": "List of users.",
              "tags": [
                  "v1_users"
              ]
          },

[jlowin]

That error means your API is returning null for a field that the schema says isn’t nullable, and is being evaluated in the low level SDK so we can’t improve the error message. If you can confirm that the schema says nullable and FastMCP is incorrectly changing to non-nullable, then we can address. We have a new test suite for this specific issue. Otherwise this is an issue with the API itself which we’ve also seen.

[thedevd]

I would say, my API schema says that input params are nullable as required is false for all of them. And also my API works fine without passing any params if tried directly using swagger

And forgot to mention that, with last version 2.10.6, I did not observe input schema validation error for same API which I am trying.
See this works-

But with 2.11.0, input schema validation is reported -

Anyway, how to verify if FastMCP is changing them to non-nullable or keeping them nullable when parsing the schema ?

[thedevd]

Hi @jlowin , I am really clueless about fastpmcp and openapi compatibility. Can you please help as this has just blocked something very important at my end. (If you see above it works with fastmcp 2.10.6)

I am trying 2.11.2 with other small set of APIs which works flawlessly when executed manually and without passing anything, but same failing with Input schema validation error.

{
    "openapi": "3.0.0",
...
....
"paths": {
....
....
"/products/count": {
            "get": {
                "tags": [
                    "products"
                ],
                "summary": "Count products in the market",
                "description": "",
                "operationId": "CountProducts",
                "parameters": [
                    {
                        "name": "includeInactive",
                        "in": "query",
                        "description": "If false, returns only products that are actively offered; if true, returns all products",
                        "required": false,
                        "schema": {
                            "type": "boolean",
                            "default": false
                        }
                    },
                    {
                        "name": "q",
                        "in": "query",
                        "description": "Optional query parameter to define a query filter using property:value syntax",
                        "required": false,
                        "schema": {
                            "type": "string",
                            "nullable": true
                        }
                    },
                    {
                        "name": "p",
                        "in": "query",
                        "description": "Optional query parameter to define a partial string match filter using property:value syntax",
                        "required": false,
                        "schema": {
                            "type": "string",
                            "nullable": true
                        }
                    },
                    {
                        "name": "limit",
                        "in": "query",
                        "description": "Optional parameter indicating maximum number to count. If the actual number is greater than the specified limit, the result will be shown as bounded.",
                        "required": false,
                        "schema": {
                            "type": "integer",
                            "nullable": true
                        }
                    }
                ],

[jlowin]

As I said, this is not being raised in FastMCP, it's being raised by the schema validation in the low-level SDK, which was bumped between FastMCP 2.10 and FastMCP 2.11. Keep in mind, required=False is not the same as nullable=True. If your API is returning a null for a field that is declared as a str, you will see that error. There is no way to disable this as far as I know in the low-level SDK other than modifying your schema so that it agrees with what your API is sending.

[thedevd]

Hi @jlowin Are you referring API output schema when you sau - If your API is returning a null for a field that is declared as a str, you will see that error.

Actually I am referring to input request API Schema defined as parameters and for input schema validation I am seeing this problem. Anyway, last time you said - If you can confirm that the schema says nullable and FastMCP is incorrectly changing to non-nullable, then we can address, so how can I check or print what schema FastMCP has parsed from openapi specs if I am running fastmcp using sse protocol (Sorry to ask this dumb question, may be I missed it from fastmcp python sdk)

[JustinGrote]

@jlowin I ran into the same thing. Is there any way to get any detail as to where the validation failed? I have a giant response with 40 properties

[JustinGrote]

Probably a dupe of #1385, I can confirm Tenable doesn't define nullable where null values might appear, so there needs to be a compatibility option.