new-mcp-tool— agent skill

Create a new MCP tool following project conventions. Use $ARGUMENTS for the tool name and description.

Steps

1. Create tool class in the appropriate tools directory

• Static class with [McpServerToolType] attribute
• Static method with [McpServerTool(Name = "snake_case_name")] attribute
• Add [Description("...")] on EVERY parameter
• Use flat parameters (no complex objects)
• Nullable optional service injection for wallet services
• Include IsConfigured check — return error result if required service not configured

1. Add models to the appropriate models file if needed

• Request/response records

1. Add service interface method in the service interface if the tool needs business logic beyond direct API calls

1. Implement service method in the implementation class

1. Update DI registration in Program.cs if new services are needed

1. Write tests following existing test patterns

Patterns to Follow

[McpServerToolType]
public static class MyNewTool
{
    [McpServerTool(Name = "my_new_tool")]
    [Description("What this tool does")]
    public static async Task<string> Execute(
        [Description("Parameter description")] string requiredParam,
        [Description("Optional parameter")] string? optionalParam = null,
        IMyService? myService = null)
    {
        if (myService is null || !myService.IsConfigured)
            return "Error: MyService is not configured. Set MY_ENV_VAR environment variable.";

        // Implementation
        return JsonSerializer.Serialize(result, new JsonSerializerOptions { WriteIndented = true });
    }
}

Key Conventions

• Tool name: snake_case (e.g., get_btc_price, check_wallet_balance)
• Class name: PascalCase + "Tool" suffix
• Return JSON-serialized results for structured data
• Use [Description] on every parameter — MCP clients use these for documentation
• Wallet priority: LND > NWC > Strike > OpenNode
• L402 requires preimage — only works with LND, Strike, CoinOS NWC, CLINK NWC, Alby Hub NWC

Free vs Paid

• 15 free tools (no license needed)
• 2 producer tools require Agentic Commerce subscription ($99/mo+): create_l402_challenge, verify_l402_payment
• If the new tool should be paid, add license check logic

Suggested follow-up: /mcp-publish-prep when ready to publish