Design tools the model can use correctly

Overview

A tool description is part of the model's operational interface. Narrow operations with typed inputs and bounded results are easier to select and validate than a generic “execute anything” function. Structured output gives application code an explicit result shape.

Descriptions help the model choose; validation protects execution

Describe when the lookup should be used, what a request ID looks like, and what a not-found result means. Keep the inputs limited to business values. Validate them in code, because descriptions influence model behavior but cannot enforce authorization, input length or identifier format. The illustrated middleware shows where tool-call behavior can be observed or constrained.

Return useful facts in a bounded shape

A result should expose the fields the assistant needs, such as identifier, status and summary, without dumping an entire database row or sensitive internal record. A structured result makes not-found and error cases distinguishable. A mutation such as closing a request should be a separate operation with separate validation, so “look up a request” cannot unexpectedly change it.

Design the lookup contract

Download the Operations Desk source. The README lists project setup, package prerequisites and local ports.

1. Describe what each function does, required identifiers, and side effects. Separate lookup, draft and commit operations.
2. Return typed records and explicit not-found/conflict results. Validate identifiers and authorization in trusted code before touching storage.
3. For mutations, pass an application request/idempotency key and record the outcome. Validate structured model output before using it as an instruction to a business service.

var agent = originalAgent
    .AsBuilder()
    .Use(async (agent, context, next, ct) =>
    {
        Console.WriteLine($"Calling: {context.Function.Name}");
        var result = await next(context, ct);
        Console.WriteLine($"Result: {result}");
        return result;
    })
    .Build();

Go deeper

Explore the related documentation.

• FabrCore Tools
• FabrCore Mcp
• FabrCore Agent Framework
• Function Calling Middleware