Key point
The one test
Use an agent when the model must choose the next step after seeing tool results. Use a script when the steps are known in advance.
A script is not a downgrade. For many hackathon features, it is safer, cheaper, and easier to debug.
When agents fit
An agent fits when the path changes based on messy input or tool results. Example: a support assistant that reads a complaint, checks order status, decides whether to ask a follow-up question, then drafts a reply.
The model is useful here because it makes judgments between steps. It decides whether to call a tool based on the user request and the tool description.