Why should you care?

This is how agents fetch orders, create tickets, or search docs without inventing data.

See it live — copy this example

Use .NET 8+. Run Semantic Kernel samples in a console or Web API. Keep API keys in user secrets or environment variables — never in source.

using System.ComponentModel;
using Microsoft.SemanticKernel;

public class OrdersPlugin
{
    [KernelFunction, Description("Get order status by id")]
    public string GetStatus([Description("Order id")] string orderId)
        => $"Order {orderId}: Shipped"; // replace with real service
}

// builder.Plugins.AddFromType<OrdersPlugin>();

What happened?

• KernelFunction marks a tool.
• Description helps the model choose it.
• You still enforce auth in the method body.

Practice next

1. Add OrdersPlugin to a kernel.
2. Invoke the function directly from C# first.
3. Then let a prompt request the status.
4. Add GetCustomerOrders(customerId).
5. Return a short summary string only.

Remember

Native functions = real C# tools. Descriptions guide tool choice. Validate inputs in code.

Order tool

Support agent must not invent shipment status.

Outcome: Status comes from GetStatus only.