How to build your first Claude agent. The part most tutorials leave out.

Building a basic Claude agent is simpler than most tutorials make it look. The pattern: write Python functions for the things you want the agent to be able to do (search the web, read a file, call an API), register them as tools, give the agent a task, run it. The agent reasons about which tools to call and in what order to complete the task. The part that most beginner tutorials skip: what happens when a tool fails. If your "search" function returns no results, what should the agent do? Try a different query? Tell the user it couldn't find anything? The agent can only make that decision if your tool communicates failure in a way the agent can understand. Raising an exception usually stops the whole thing. Returning structured output with an error flag gives the agent something to work with. Getting comfortable with the failure cases is what takes a toy agent to a useful one. The happy path is easy. The edge cases are where you learn. What failure cases have you hit in early agent projects that you wish you'd been warned about?