Implementation of Custom Tool in MCP #3048

souvikghosh04 · 2026-01-12T11:15:53Z

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)

List All Tools (also includes custom tool)

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

Get Books (no parameters)

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

Get Book by ID

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

Insert Book

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

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
}

Non-Existent Tool

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

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
}

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
}

Empty String

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

Invalid Type (string for int)

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

Negative ID

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

Maximum Integer

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

Case Sensitivity (should fail)

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

- Add EntityMcpOptions class with custom-tool and dml-tools properties - Add JSON converter supporting boolean and object formats - Add CLI support for --mcp.dml-tools and --mcp.custom-tool flags - Add schema validation restricting custom-tool to stored procedures - Entity.Mcp property is optional (default null) to avoid test cascade Only 9 files changed in this minimal implementation.

- Update EntityMcpOptions documentation to clarify custom-tool behavior in boolean mode - Replace if-else with switch-case in converter for better extensibility - Remove unnecessary null writes in serializer - Change CustomToolEnabled and DmlToolEnabled from nullable to non-nullable bool - Fix boolean shorthand deserialization to not mark custom-tool as user-provided - Add consistent else block in constructor for symmetry All 530 tests passing. Functionality verified with manual testing.

…/Azure/data-api-builder into Usr/sogh/entity-level-mcp-config

…ated updates

…c-10dec2025

souvikghosh04 · 2026-01-12T11:16:34Z

/azp run

azure-pipelines · 2026-01-12T11:17:03Z

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

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs

src/Azure.DataApiBuilder.Mcp/Core/McpServiceCollectionExtensions.cs

src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs

src/Azure.DataApiBuilder.Mcp/Core/CustomMcpToolFactory.cs

src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs

src/Azure.DataApiBuilder.Mcp/Core/McpServiceCollectionExtensions.cs

src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs

souvikghosh04 · 2026-01-13T12:37:07Z

/azp run

azure-pipelines · 2026-01-13T12:37:34Z

Azure Pipelines successfully started running 6 pipeline(s).

souvikghosh04 · 2026-01-13T12:45:47Z

/azp run

azure-pipelines · 2026-01-13T12:46:12Z

Azure Pipelines successfully started running 6 pipeline(s).

JerryNixon · 2026-01-13T21:57:49Z

src/Azure.DataApiBuilder.Mcp/Core/DynamicCustomTool.cs

+        /// <summary>
+        /// Executes the stored procedure represented by this custom tool.
+        /// </summary>
+        public async Task<CallToolResult> ExecuteAsync(


Important

Please add explicit OpenTelemetry tracing for custom stored-procedure MCP tools.

Scope: DynamicCustomTool.ExecuteAsync(...)

Requirements:

Create an Activity/span around each tool invocation (e.g., span name mcp.tool.call or dab.mcp.custom_tool.execute).

Add span attributes/tags at minimum:

mcp.tool.name = tool name

dab.entity = entity alias/name

dab.operation = execute

db.procedure (or equivalent) = stored procedure name / db object (schema-qualified if available)

Record outcome on the span:

mark success vs failure (ActivityStatusCode.Ok / Error)

on exceptions, record the exception on the span and include an error message/code where available.

Notes:

Logging via ILogger is not sufficient; the tool should emit tracing spans directly.

Ensure spans are created for both success and failure paths (including auth/validation failures).

PLEASE TREAT TELEMETRY AS A BASE REQUIREMENT

Please implement OpenTelemetry tracing for MCP tool execution centrally to avoid duplicating instrumentation in every tool.

Goal: Every MCP tools/call invocation (built-in DML tools and dynamic custom stored-proc tools) emits a consistent span.

General idea:

Add instrumentation in the MCP dispatcher / tool execution entry point (the code path that resolves the tool by name and invokes IMcpTool.ExecuteAsync).

Start an Activity span for each tool call (e.g., mcp.tool.call / dab.mcp.tool.execute) and ensure it wraps the entire execution including auth/validation and query execution.

Apply standard tags (e.g., mcp.tool.name, dab.entity when applicable, dab.operation, db.procedure when applicable).

Set span status to Ok/Error and record exceptions.

Agree on this - but we can add it in a separate subsequent PR - for easier PR review and merge process.

souvikghosh04 added 19 commits December 4, 2025 16:15

Validate MCP options if provided

c186dc2

Merge branch 'main' into Usr/sogh/entity-level-mcp-config

aebe80e

Copilot review fixes

0514f58

Merge branch 'Usr/sogh/entity-level-mcp-config' of https://github.com…

4446274

…/Azure/data-api-builder into Usr/sogh/entity-level-mcp-config

Added tests for Entity MCP config

ac12ece

Merge branch 'main' into Usr/sogh/entity-level-mcp-config

271f896

Added additional tests and fixes

f30ef6f

Merge branch 'Usr/sogh/entity-level-mcp-config' of https://github.com…

372595b

…/Azure/data-api-builder into Usr/sogh/entity-level-mcp-config

Fix formattings

f032963

POC for custom tool

78d76d6

Merge latest changes from main branch - MCP dml-tools support and rel…

b56e748

…ated updates

POC tests and artifacts

a3e3dc1

Merge remote-tracking branch 'origin/main' into Usr/sogh/customtoolpo…

c78d102

…c-10dec2025

Refactorings

7f7b431

Remove temp test artifacts

c2c90e7

Remove temp/duplicate test snapshot files

7dc5c65

Revert temp changes from dab config

b9fb4d0

souvikghosh04 requested a review from Copilot January 12, 2026 11:16

souvikghosh04 self-assigned this Jan 12, 2026

Copilot started reviewing on behalf of souvikghosh04 January 12, 2026 11:16 View session

souvikghosh04 added mcp-server mssql an issue thats specific to mssql labels Jan 12, 2026

souvikghosh04 added this to the Jan 2026 milestone Jan 12, 2026

souvikghosh04 added this to Data API builder Jan 12, 2026

github-project-automation bot moved this to Todo in Data API builder Jan 12, 2026

souvikghosh04 linked an issue Jan 12, 2026 that may be closed by this pull request

Implement functionality for Custom Tool in MCP #2877

Open

Copilot AI reviewed Jan 12, 2026

View reviewed changes

souvikghosh04 changed the title ~~Usr/sogh/customtoolpoc 10dec2025~~ Implementation of Custom Tool in MCP Jan 12, 2026

souvikghosh04 added 2 commits January 12, 2026 21:42

Formatting

6304421

Added GHCP review changes

0b2e517

Fix formatting

d4e6549

souvikghosh04 moved this from Todo to In Progress in Data API builder Jan 13, 2026

souvikghosh04 marked this pull request as ready for review January 13, 2026 15:10

souvikghosh04 requested review from Alekhya-Polavarapu, Aniruddh25, RubenCerna2079, aaronburtle, anushakolan, neeraj-sharma2592, rusamant, sourabh1007 and vadeveka as code owners January 13, 2026 15:10

JerryNixon requested changes Jan 13, 2026

View reviewed changes

github-project-automation bot moved this from In Progress to Review In Progress in Data API builder Jan 13, 2026

souvikghosh04 mentioned this pull request Jan 14, 2026

MCP Custom Tool Telemetry #3060

Open

Implementation of Custom Tool in MCP #3048

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Implementation of Custom Tool in MCP #3048

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souvikghosh04 commented Jan 12, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Why make this change?

What is this change?

How was this tested?

Sample Request(s)

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souvikghosh04 commented Jan 12, 2026

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Pull request overview

Reviewed changes

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souvikghosh04 commented Jan 13, 2026

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Important

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JerryNixon Jan 13, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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PLEASE TREAT TELEMETRY AS A BASE REQUIREMENT

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JerryNixon Jan 13, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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souvikghosh04 commented Jan 12, 2026 •

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