Implementation of Custom Tool in MCP by souvikghosh04 · Pull Request #3048 · Azure/data-api-builder

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).

…/Azure/data-api-builder into Usr/sogh/customtoolpoc-10dec2025

anushakolan

LGTM!

Aniruddh25 · 2026-01-16T21:06:20Z

/azp run

azure-pipelines · 2026-01-16T21:06:49Z

Azure Pipelines successfully started running 6 pipeline(s).

Aniruddh25

Nullability of the config parameter type has inconsistent expectations.

Co-authored-by: Aniruddh Munde <anmunde@microsoft.com>

souvikghosh04 · 2026-01-17T14:25:09Z

/azp run

azure-pipelines · 2026-01-17T14:25:33Z

Azure Pipelines successfully started running 6 pipeline(s).

souvikghosh04 · 2026-01-17T14:25:48Z

/azp run

azure-pipelines · 2026-01-17T14:26:12Z

Azure Pipelines successfully started running 6 pipeline(s).

…/Azure/data-api-builder into Usr/sogh/customtoolpoc-10dec2025

souvikghosh04 · 2026-01-20T05:05:43Z

/azp run

azure-pipelines · 2026-01-20T05:06:08Z

Azure Pipelines successfully started running 6 pipeline(s).

…l since config cannot be null and as suggested in PR review comment

souvikghosh04 · 2026-01-20T15:35:29Z

/azp run

azure-pipelines · 2026-01-20T15:35:56Z

Azure Pipelines successfully started running 6 pipeline(s).

Ani has already reviewed it twice. Since he is OOF and all comments are addressed dismissing this to unblock the PR.

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

Closed

souvikghosh04 added 3 commits January 16, 2026 14:56

Fix tests, nits and minor changes

7372fb3

Merge branch 'Usr/sogh/customtoolpoc-10dec2025' of https://github.com…

3b16969

…/Azure/data-api-builder into Usr/sogh/customtoolpoc-10dec2025

Merge branch 'main' into Usr/sogh/customtoolpoc-10dec2025

ad4ebaa

souvikghosh04 requested a review from Aniruddh25 January 16, 2026 09:32

anushakolan reviewed Jan 16, 2026

View reviewed changes

anushakolan approved these changes Jan 16, 2026

View reviewed changes

Aniruddh25 previously requested changes Jan 16, 2026

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Apply suggestion from @Aniruddh25

e144129

Co-authored-by: Aniruddh Munde <anmunde@microsoft.com>

Merge branch 'main' into Usr/sogh/customtoolpoc-10dec2025

5cd8593

souvikghosh04 requested a review from Aniruddh25 January 17, 2026 14:25

souvikghosh04 added 2 commits January 20, 2026 10:33

Fix Unit test

f5b48bb

Merge branch 'Usr/sogh/customtoolpoc-10dec2025' of https://github.com…

a08b84b

…/Azure/data-api-builder into Usr/sogh/customtoolpoc-10dec2025

removed test CreateCustomTools_ReturnsEmptyCollection_WhenConfigIsNul…

96cd240

…l since config cannot be null and as suggested in PR review comment

souvikghosh04 enabled auto-merge (squash) January 20, 2026 16:37

anushakolan approved these changes Jan 21, 2026

View reviewed changes

souvikghosh04 merged commit 3cf09f9 into main Jan 22, 2026
11 checks passed

souvikghosh04 deleted the Usr/sogh/customtoolpoc-10dec2025 branch January 22, 2026 05:14

github-project-automation bot moved this from Review In Progress to Done in Data API builder Jan 22, 2026

Copilot AI mentioned this pull request Feb 6, 2026

Add centralized OpenTelemetry tracing for MCP tool execution #3111

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