cached-mcp-tool-provider

Chapter 5 -- CachedMcpToolProvider (Critical-1 fix)

Companion code for Generative AI in .NET, Chapter 5 (~line 1384) and the Critical-1 fix from review-action-plan.md.

A small helper that caches the tool list returned by an McpClient and invalidates the cache when the server emits a notifications/tools/list_changed notification.

This sample exists primarily so readers can see the corrected class -- the original draft had a constructor chaining bug (public CachedMcpToolProvider(McpClient client) : this(client) -- recursive). The fixed version assigns the field directly from the parameter and subscribes to the change-notification stream.

Run it

The demo requires a real MCP server to connect to. Pass the spawn command as arguments:

dotnet run --project samples/ch05-mcp/cached-mcp-tool-provider -- dnx Microsoft.Azure.Mcp --yes

Or use any other stdio-based MCP server. Expected output:

First call -- fetches from server.
  N tool(s):
    - tool_a
    - tool_b
    ...

Second call -- served from cache.
  N tool(s) (cached=True)

Manuscript reference

• Manuscript/Chapter-05.md, section 5.4.2 (~line 1384).
• Manuscript/review-01.md, item C1.

Prerequisites

• .NET 9 SDK
• An MCP server you can spawn over stdio (Azure MCP, the 05.3.2-sse-transport sample's HTTP version, etc.)