AI agent tool calling: designing tools the model will actually use correctly

You give your agent a handful of tools, write a decent system prompt and try a few requests. It works. Then real users show up. The agent calls search when it should have called get_order. It passes a customer name where an ID was expected. It retries the same failing call five times in a row. It dumps a 40,000 token API response into its own context and forgets what the user asked. The usual reaction is to blame the model or pile more instructions into the system prompt. Most of the time the r