Module
Module 3 of 7Lesson 2 of 2~17 min

Specify tool errors and idempotency

Lesson 2 of the module "Design tools the model uses well" in the course "Design reliable agents and tool calling".

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Lesson objective

By the end of this lesson, you will be able to specify the error messages a tool returns to the agent, make tools with side effects idempotent and describe the expected behaviour on timeout or partial failure.

Where it fits

Design tools the model uses well

Which tools should the agent get, how should they be described, and what happens when they fail?

Lessons in this module

  1. Write tool cards the model uses well
  2. Specify tool errors and idempotency (this lesson)

What you will learn in the course

This lesson is part of the course Design reliable agents and tool calling

  • Decide, with explicit criteria, whether a use case calls for a single call, a workflow or an agent, and choose the right pattern.
  • Write tool cards the model uses well (name, description, parameters, return, errors, idempotency, risk level).
  • Specify an agent's loop (goal, context, stop conditions, budgets, error handling) and judge whether an orchestrator and subagents are warranted.
  • Place human approval points and an agent's permissions according to the blast radius of each action.
  • Identify prompt-injection paths through tool outputs and specify structural mitigations that do not rely on the prompt alone.
  • Specify the trace of a run and the evaluation of an agent (task success, trajectory, cost, latency, consistency over several trials).

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