Adding a Tool

1. Create the tool

Create src/RoslynLens/Tools/MyTool.cs:

using System.ComponentModel;
using ModelContextProtocol.Server;
using RoslynLens.Responses;

namespace RoslynLens.Tools;

[McpServerToolType]
public static class MyTool
{
    [McpServerTool("my_tool"), Description("Short description of what this tool does.")]
    public static async Task<string> Execute(
        WorkspaceManager workspace,
        [Description("Parameter description")] string paramName,
        [Description("Optional filter")] string? optionalParam = null,
        CancellationToken cancellationToken = default)
    {
        if (workspace.State != WorkspaceState.Ready)
            return "Workspace is still loading. Please try again shortly.";

        var solution = workspace.CurrentSolution;
        if (solution is null)
            return "No solution loaded.";

        // Your Roslyn logic here
        var results = new List<SymbolLocation>();

        // ... query the solution ...

        return results.Count == 0
            ? "No results found."
            : string.Join("\n", results);
    }
}

Conventions

• Tool name: snake_case (MCP convention)
• Description: One sentence, shown to Claude as tool documentation
• Check workspace state: Always return a helpful message if not Ready
• Token efficiency: Return minimal, structured text — not full file contents
• CancellationToken: Always accept it as last parameter

2. Registration

Tools are auto-discovered by WithToolsFromAssembly() via the [McpServerToolType] attribute. No manual registration needed.

3. Verify

dotnet build

Test the tool appears in the tool list:

claude mcp list

Then ask Claude to use it in a conversation.