[BUG] MCP - Cannot Read Properties Of Undefined (reading 'type')

by ADMIN 65 views

BUG: MCP - Cannot Read Properties of Undefined (Reading 'type')

Describe the Bug

The MCP tool is throwing a TypeError: Cannot read properties of undefined (reading 'type') error when trying to process the input schema of a tool. This error occurs when the type property is accessed on an object that is undefined.

Steps To Reproduce

To reproduce this issue, you can use the MCP tool with a tool description that contains an input schema with a type property that is set to array, but without a corresponding items key. Here is an example of a tool description that triggers this error:

{
  "tools": [
    {
      "description": "List all sheets in an Excel file",
      "inputSchema": {
        "properties": {
          "file_id": {
            "type": "string",
            "description": "The ID of the Excel file in OneDrive"
          }
        },
        "required": [
          "file_id"
        ],
        "type": "object"
      },
      "name": "list-sheets"
    }
  ]
}

In this example, the type property is set to object, but the properties object is missing the items key, which is required for an array type.

Expected Behavior

The MCP tool should not throw an exception when processing the input schema of a tool.

Environment Information

This issue was reported on a Mac OS system with a modern version of Node.js.

Component

Agents

Code Snippet

// No code snippet provided

Error Logs

// No error logs provided

Additional Context

No additional context was provided.

Verification

  • [x] I have searched the existing issues to make sure this is not a duplicate
  • [x] I have included sufficient information for the team to reproduce and understand the issue

Possible Causes

  1. Missing items key: The items key is required for an array type in the input schema. If this key is missing, the MCP tool will throw an exception when trying to access the type property.
  2. Incorrect type property: The type property is set to object, but the properties object is missing the items key. This can cause the MCP tool to throw an exception when trying to access the type property.

Solution

To fix this issue, you need to add the items key to the properties object in the input schema. Here is an example of the corrected input schema:

{
  "tools": [
    {
      "description": "List all sheets in an Excel file",
      "inputSchema": {
        "properties": {
          "file_id": {
            "type": "string",
            "description": "The ID of the Excel file in OneDrive"
          }
        },
        "required": [
          "file_id"
        ],
        "type": "object",
        "items": {
          "type": "string"
        }
      },
      "name": "list-sheets"
    }
  ]
}

In this example, the items key is added to the properties object, and the type property is set to string. This should the issue and prevent the MCP tool from throwing an exception.
Q&A: MCP - Cannot Read Properties of Undefined (Reading 'type')

Q: What is the MCP tool and what is its purpose?

A: The MCP tool is a software tool used for automating tasks and workflows. Its purpose is to provide a simple and intuitive way to create, manage, and execute tasks, making it easier to automate repetitive tasks and workflows.

Q: What is the error "Cannot read properties of undefined (reading 'type')" and how does it occur?

A: The error "Cannot read properties of undefined (reading 'type')" occurs when the MCP tool tries to access the type property of an object that is undefined. This can happen when the input schema of a tool is not properly formatted or when there is a mismatch between the expected and actual data types.

Q: What are the possible causes of this error?

A: The possible causes of this error are:

  1. Missing items key: The items key is required for an array type in the input schema. If this key is missing, the MCP tool will throw an exception when trying to access the type property.
  2. Incorrect type property: The type property is set to object, but the properties object is missing the items key. This can cause the MCP tool to throw an exception when trying to access the type property.

Q: How can I fix this error?

A: To fix this error, you need to add the items key to the properties object in the input schema. Here is an example of the corrected input schema:

{
  "tools": [
    {
      "description": "List all sheets in an Excel file",
      "inputSchema": {
        "properties": {
          "file_id": {
            "type": "string",
            "description": "The ID of the Excel file in OneDrive"
          }
        },
        "required": [
          "file_id"
        ],
        "type": "object",
        "items": {
          "type": "string"
        }
      },
      "name": "list-sheets"
    }
  ]
}

In this example, the items key is added to the properties object, and the type property is set to string. This should fix the issue and prevent the MCP tool from throwing an exception.

Q: What are some best practices for using the MCP tool?

A: Some best practices for using the MCP tool include:

  1. Use the correct data types: Make sure to use the correct data types for each property in the input schema.
  2. Add the items key: If you are using an array type, make sure to add the items key to the properties object.
  3. Test your tools: Test your tools thoroughly to ensure that they are working correctly and not throwing any errors.

Q: Where can I find more information about the MCP tool?

A: You can find more information about the MCP tool on the official documentation website. The documentation includes tutorials, guides, and reference materials to help you get started with using the MCP tool.

Q: How can I report a bug or issue with the MCP tool?

A: If you encounter a bug or issue with the MCP tool, you can it to the development team by submitting a bug report. The bug report should include a detailed description of the issue, including any error messages or stack traces.