Implementation of Custom Tool in MCP

[souvikghosh04]

Why make this change?

• Closes on - Implement functionality for Custom Tool in MCP #2877

What is this change?

This pull request introduces a new system for dynamically generating and registering custom MCP tools based on stored procedure entity configurations in the runtime configuration. The main changes are the implementation of the DynamicCustomTool class, a factory to create these tools from configuration, and the necessary service registration logic to ensure these custom tools are available at runtime.

Dynamic custom MCP tool support:

• Added the DynamicCustomTool class, which implements IMcpTool and provides logic for generating tool metadata, validating configuration, handling authorization, executing the underlying stored procedure, and formatting the response. This enables each stored procedure entity with custom-tool enabled to be exposed as a dedicated MCP tool.
• Introduced the CustomMcpToolFactory class, which scans the runtime configuration for stored procedure entities marked with custom-tool enabled and creates corresponding DynamicCustomTool instances.

Dependency injection and service registration:

• Updated the MCP server startup (AddDabMcpServer) to register custom tools generated from configuration by calling a new RegisterCustomTools method after auto-discovering static tools.
• Modified the RegisterAllMcpTools method to exclude DynamicCustomTool from auto-discovery (since these are created dynamically per configuration) and added the RegisterCustomTools method to register each generated custom tool as a singleton service.

How was this tested?

• Unit Tests
• Manual Tests using Insomnia and VS code GHCP chat

Sample Request(s)

1. List All Tools (also includes custom tool)

{
  "jsonrpc": "2.0",
  "method": "tools/list",
  "params": {},
  "id": 1
}

2. Get Books (no parameters)

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_books"
  },
  "id": 2
}

3. Get Book by ID

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_book",
    "arguments": {
      "id": 1
    }
  },
  "id": 3
}

4. Insert Book

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "insert_book",
    "arguments": {
      "title": "Test Book from MCP",
      "publisher_id": "1234"
    }
  },
  "id": 4
}

5. Count Books (no parameters)

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "count_books"
  },
  "id": 5
}

Error Scenarios
6. Missing Required Parameter

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_book"
  },
  "id": 6
}

7. Non-Existent Tool

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "non_existent_tool"
  },
  "id": 7
}

8. Invalid Foreign Key

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "insert_book",
    "arguments": {
      "title": "Test Book",
      "publisher_id": "999999"
    }
  },
  "id": 8
}

Edge Cases
9. SQL Injection Attempt

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_book",
    "arguments": {
      "id": "1; DROP TABLE books; --"
    }
  },
  "id": 9
}

11. Special Characters

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "insert_book",
    "arguments": {
      "title": "Test Book with 'quotes' and \"double quotes\" and <tags>",
      "publisher_id": "1234"
    }
  },
  "id": 10
}

12. Empty String

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "insert_book",
    "arguments": {
      "title": "",
      "publisher_id": "1234"
    }
  },
  "id": 11
}

13. Invalid Type (string for int)

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_book",
    "arguments": {
      "id": "not_a_number"
    }
  },
  "id": 12
}

14. Negative ID

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_book",
    "arguments": {
      "id": -1
    }
  },
  "id": 13
}

15. Maximum Integer

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_book",
    "arguments": {
      "id": 2147483647
    }
  },
  "id": 14
}

16. Case Sensitivity (should fail)

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "GET_BOOKS"
  },
  "id": 15
}

[souvikghosh04]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).

[Copilot]

Pull request overview

This PR introduces dynamic custom MCP tool support, allowing stored procedures configured with "custom-tool" enabled to be automatically exposed as dedicated MCP tools. The implementation adds a factory pattern for generating tools from configuration and integrates them into the service registration pipeline.

Changes:

• Added DynamicCustomTool class to dynamically generate MCP tools from stored procedure configurations
• Implemented CustomMcpToolFactory to scan runtime configuration and create custom tools
• Updated service registration in McpServiceCollectionExtensions to exclude dynamic tools from auto-discovery and register custom tools from configuration

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 14 comments.

File	Description
src/Azure.DataApiBuilder.Mcp/Core/McpServiceCollectionExtensions.cs	Added RegisterCustomTools method and modified auto-discovery to exclude DynamicCustomTool
src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs	New class implementing IMcpTool for dynamically generated stored procedure tools
src/Azure.DataApiBuilder.Mcp/Core/CustomMcpToolFactory.cs	New factory class for creating custom tools from runtime configuration

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[souvikghosh04]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).

[souvikghosh04]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).