Level 3 · 40 min

Agents & Tool Use: Loops, Plans, Failures

An agent is a control loop around a model: observe, plan, call tools, inspect results, and stop. The model is not the whole system; tool schemas, permissions, budgets, and termination conditions decide reliability.

Mental model for agents and tool use

Agents & Tool Use: Loops, Plans, Failures is useful only when you can explain the abstraction and its failure boundary. Start by naming inputs, outputs, guarantees, and what the component refuses to guarantee. That framing prevents cargo-cult use of a technique that happens to be popular.

Production design questions

For a senior interview, connect the concept to reliability, latency, cost, security, and observability. Explain what you would measure, what assumption could break first, and how you would roll out a change safely.

Common failure mode

The common mistake is treating agents and tool use as a black box. When the system fails, you need enough internal model to inspect inputs, intermediate state, and outputs without guessing.

Key Takeaways

Define the exact guarantee provided by agents and tool use.
Tie the concept to measurable production behavior, not only textbook definitions.
Name the failure mode and the signal you would monitor before shipping.

Code example

Checklist:
1. Define the user-facing goal
2. State the system guarantee
3. Identify assumptions
4. Add measurement
5. Test the most likely failure mode