MCPTool/server parsing error

[keiserS]

Bug Report

Overview

When in the list of tools, I added the MCP tool with the address: 'https://mcp.deepwiki.com/mcp'

 var tools = new List<Tool>
            {
                Tool.GetOrCreateTool(typeof(DateTimeUtility), nameof(DateTimeUtility.GetDateTime)),
                new MCPTool("deepwiki", "https://mcp.deepwiki.com/mcp")
                //new MCPTool("my_mcp_server", "https://localhost:7295/mcp")  
            };

I got this error on running that AI response (class Program already posted here: Bug report #486

Failed to parse Response -> {
  "id": "resp_68d00339b320819c983bba521592dd0700a1a74376246095",
  "object": "response",
  "created_at": 1758462777,
  "status": "completed",
  "background": false,
  "error": null,
  "incomplete_details": null,
  "instructions": null,
  "max_output_tokens": null,
  "max_tool_calls": null,
  "model": "gpt-4.1-nano-2025-04-14",
  "output": [
    {
      "id": "mcpl_68d00339d8bc819c9a24c51eabf42e5400a1a74376246095",
      "type": "mcp_list_tools",
      "server_label": "deepwiki",
      "tools": [
        {
          "annotations": {
            "read_only": false
          },
          "description": "Get a list of documentation topics for a GitHub repository",
          "input_schema": {
            "type": "object",
            "properties": {
              "repoName": {
                "type": "string",
                "description": "GitHub repository: owner/repo (e.g. \"facebook/react\")"
              }
            },
            "required": [
              "repoName"
            ],
            "additionalProperties": false,
            "$schema": "http://json-schema.org/draft-07/schema#"
          },
          "name": "read_wiki_structure"
        },
        {
          "annotations": {
            "read_only": false
          },
          "description": "View documentation about a GitHub repository",
          "input_schema": {
            "type": "object",
            "properties": {
              "repoName": {
                "type": "string",
                "description": "GitHub repository: owner/repo (e.g. \"facebook/react\")"
              }
            },
            "required": [
              "repoName"
            ],
            "additionalProperties": false,
            "$schema": "http://json-schema.org/draft-07/schema#"
          },
          "name": "read_wiki_contents"
        },
        {
          "annotations": {
            "read_only": false
          },
          "description": "Ask any question about a GitHub repository",
          "input_schema": {
            "type": "object",
            "properties": {
              "repoName": {
                "type": "string",
                "description": "GitHub repository: owner/repo (e.g. \"facebook/react\")"
              },
              "question": {
                "type": "string",
                "description": "The question to ask about the repository"
              }
            },
            "required": [
              "repoName",
              "question"
            ],
            "additionalProperties": false,
            "$schema": "http://json-schema.org/draft-07/schema#"
          },
          "name": "ask_question"
        }
      ]
    },
    {
      "id": "msg_68d0033cc450819cbcffdeb84c6166e100a1a74376246095",
      "type": "message",
      "status": "completed",
      "content": [
        {
          "type": "output_text",
          "annotations": [],
          "logprobs": [],
          "text": "Hello! How can I help you today?"
        }
      ],
      "role": "assistant"
    }
  ],
  "parallel_tool_calls": true,
  "previous_response_id": null,
  "prompt_cache_key": null,
  "reasoning": {
    "effort": null,
    "summary": null
  },
  "safety_identifier": null,
  "service_tier": "default",
  "store": true,
  "temperature": 1.0,
  "text": {
    "format": {
      "type": "text"
    },
    "verbosity": "medium"
  },
  "tool_choice": "auto",
  "tools": [
    {
      "type": "function",
      "description": null,
      "name": "GetDateTime_83c964258964c5b11c046b612a4beb40",
      "parameters": {
        "type": "object",
        "properties": {},
        "additionalProperties": false,
        "required": []
      },
      "strict": true
    },
    {
      "type": "mcp",
      "allowed_tools": null,
      "headers": null,
      "require_approval": "always",
      "server_description": null,
      "server_label": "deepwiki",
      "server_url": "https://mcp.deepwiki.com/<redacted>"
    }
  ],
  "top_logprobs": 0,
  "top_p": 1.0,
  "truncation": "auto",
  "usage": {
    "input_tokens": 219,
    "input_tokens_details": {
      "cached_tokens": 0
    },
    "output_tokens": 11,
    "output_tokens_details": {
      "reasoning_tokens": 0
    },
    "total_tokens": 230
  },
  "user": null,
  "metadata": {}
}
System.Text.Json.JsonException: The JSON value could not be converted to System.String. Path: $.tools[0].input_schema | LineNumber: 0 | BytePositionInLine: 247.
 ---> System.InvalidOperationException: Cannot get the value of a token type 'StartObject' as a string.
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_ExpectedString(JsonTokenType tokenType)
   at System.Text.Json.Utf8JsonReader.GetString()
   at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.JsonCollectionConverter`2.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, TCollection& value)
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, Utf8JsonReader& reader, Exception ex)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.Deserialize(Utf8JsonReader& reader, ReadStack& state)
   at System.Text.Json.JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 utf8Json, JsonTypeInfo`1 jsonTypeInfo, Nullable`1 actualByteCount)
   at System.Text.Json.JsonSerializer.Deserialize[TValue](JsonElement element, JsonSerializerOptions options)
   at OpenAI.Responses.ResponseItemConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) in F:\Downloads\OpenAI-DotNet-main\OpenAI-DotNet-main\OpenAI-DotNet\Extensions\ResponseItemConverter.cs:line 35
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.JsonCollectionConverter`2.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, TCollection& value)
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.Deserialize(Utf8JsonReader& reader, ReadStack& state)
   at System.Text.Json.JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 utf8Json, JsonTypeInfo`1 jsonTypeInfo, Nullable`1 actualByteCount)
   at System.Text.Json.JsonSerializer.ReadFromNode[TValue](JsonNode node, JsonTypeInfo`1 jsonTypeInfo)
   at OpenAI.Extensions.ResponseExtensions.Deserialize[T](HttpResponseMessage response, JsonNode jNode, OpenAIClient client) in F:\Downloads\OpenAI-DotNet-main\OpenAI-DotNet-main\OpenAI-DotNet\Extensions\ResponseExtensions.cs:line 338
*********************************************************************
>>>>> StreamCallback: error OpenAI.Error
------------------------------------------
>>> Message:The JSON value could not be converted to System.String. Path: $.tools[0].input_schema | LineNumber: 0 | BytePositionInLine: 247. ()

To Reproduce

Use Program.cs from the linked report and change the list of tools.

[StephenHodgson]

Is this not a duplicate of #486 ?

[keiserS]

Is this not a duplicate of #486 ?

No, this one is a new bug reproduced with the defined MCP tool (known MCP that doesn't require authentication), but based on the same code. I think there are multiple problems in #486 and this one:

1. When "EnabledDebugging = false" there is no exception about "closed stream" (#486)
2. Error might not be propagated correctly: when @event = "error", Exception property is empty; and the next response actually has real error message. (I was testing with my MCP server implementation - might be something is wrong with my code, which I'm rewriting)
3. #487 to me seems to be a new problem with parsing the correct JSON response to objects of the library

I hope this clarifies why I reported two different bugs (although they are connected to the same code, but rather different MCP URLs).

[keiserS]

@StephenHodgson - resolution of this MCP bug
I found the issue and resolution: MCPServerTool needs a bit of adjustment in terms of properties (I didn't investigate if this was like that before!) but this is the proper class definition.
Problem was "string InputSchema { get; private set; }" property know define differently for Deserialization.

public sealed class MCPServerTool
{
    [JsonInclude]
    [JsonPropertyName("name")]
    public string Name { get; private set; }

    [JsonInclude]
    [JsonPropertyName("description")]
    public string Description { get; private set; }

    //[JsonInclude]
    //[JsonPropertyName("input_schema")]
    //public string InputSchema { get; private set; }

    [JsonInclude]
    [JsonPropertyName("input_schema")]
    public InputSchema InputSchema { get; set; }

    [JsonInclude]
    [JsonPropertyName("annotations")]
    public object Annotations { get; private set; }
}


public sealed class InputSchema
{
    [JsonPropertyName("type")]
    public string Type { get; set; }

    [JsonPropertyName("properties")]
    public Dictionary<string, JsonElement> Properties { get; set; }

    [JsonPropertyName("required")]
    public List<string> Required { get; set; }
}

So, could you check and solve this?

Regards,
K.

[StephenHodgson]

Yeah I think so. I'll try to sort it out before the next release. I plan to allocate some time to bug fixes and updates this week.

[keiserS]

Two more improvements with the classes around MCP tools (please check the code comments):

public sealed class MCPToolCall : BaseResponse, IResponseItem
{
    // ... other properties ...

    [JsonInclude]
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    [JsonPropertyName("error")]
    public MCPError? Error { get; private set; }    **// string property is not correct; it should be class property as presented**
}

public sealed class MCPError
{
    [JsonInclude]
    [JsonPropertyName("type")]
    public string? Type { get; private set; }

    [JsonInclude]
    [JsonPropertyName("code")]
    public int? Code { get; private set; }

    [JsonInclude]
    [JsonPropertyName("message")]
    public string? Message { get; private set; }
}

The next is more of an improvement, in the code:

            var tools = new List<Tool>
            {
                new MCPTool("deepwiki", "https://mcp.deepwiki.com/mcp", requireApproval: MCPRequireApproval.Never)
            }

I would add strict string value in hand as class constants:

public sealed class MCPRequireApproval
{
    public const string Never = "never";
    public const string Always = "always";
}

to avoid string typos, or just to have a list of possible values (although it's available in the comment). The last one is just the proposition to the library.