Fix typo in McpPromptRegistry and improve JSON safety

[Vagabond-K]

Description

• Fixed a typo from promtps to prompts in McpPromptRegistry.cs.
• Added a Count > 0 check to prevent exceptions when converting prompts and tools to JSON strings if no items exist. Applied the same safety improvements to McpToolRegistry.cs.

Motivation and Context

• Found that adding an MCP server fails in Visual Studio when registering MCP tools without prompts, as the absence of prompts causes the '[' character to be omitted from the resulting JSON.
• Note that in Visual Studio Code, the MCP server was still functional; unlike Visual Studio 2026, it proceeds to fetch the tool list even if the prompt list retrieval fails.

How Has This Been Tested?

nanoFramework.WebServer/tests/McpEndToEndTest/Program.cs

McpToolRegistry.DiscoverTools(new Type[] { typeof(McpServerTests.McpTools) });
Debug.WriteLine("MCP Tools discovered and registered.");

//McpPromptRegistry.DiscoverPrompts(new Type[] { typeof(McpServerTests.McpPrompts) });
//Debug.WriteLine("MCP Prompts discovered and registered.");

Screenshots

• Visual Studio 2026
  
• Visual Studio Code
  

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue with code or algorithm)
• New feature (non-breaking change which adds functionality to code)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Unit Tests (add new Unit Test(s) or improved existing one(s), has no impact on code or features)
• Documentation (changes or updates in the documentation, has no impact on code or features)

Checklist:

• My code follows the code style of this project (only if there are changes in source code).
• My changes require an update to the documentation (there are changes that require the docs website to be updated).
• I have updated the documentation accordingly (the changes require an update on the docs in this repo).
• I have read the CONTRIBUTING document.
• I have tested everything locally and all new and existing tests passed (only if there are changes in source code).
• I have added new tests to cover my changes.

[coderabbitai]

Important

Review skipped

Review was skipped due to path filters

⛔ Files ignored due to path filters (2)

• nanoFramework.WebServer.Mcp/McpPromptRegistry.cs is excluded by none and included by none
• nanoFramework.WebServer.Mcp/McpToolRegistry.cs is excluded by none and included by none

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[josesimoes]

Nice catch. The typo is on me... 😅

[Vagabond-K]

Nice catch. The typo is on me... 😅

😅
Thanks once more for all the work on this project. I think .NET nanoFramework is a fantastic project, and it's been a pleasure to contribute.