When to use tools vs prompts — CCA-F Exam Prep

L2.09|When to use tools vs prompts

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You

A developer looking at two monitors. Left monitor: a tool implementation with 200 lines of code, an API endpoint, error handling, retry logic. Right monitor: a system prompt with 5 lines that does the same thing. The developer's expression: 'I overengineered this.' Cost comparison floating above: Tool = $0.12/call, Prompt = $0.002/call.

They spent two weeks building a classification tool. Five lines in the system prompt replaced it.

A support team wanted Claude to classify incoming tickets into five categories: billing, technical, account, shipping, other. A junior engineer built a custom tool -- it called an external ML API, parsed the response, mapped categories, handled errors.

Two weeks of work. The tool added 400ms latency per ticket. It cost $0.12 per classification. It broke when the ML API had downtime.

A senior engineer added five lines to the system prompt: the five categories with descriptions. Claude classified tickets at 97% accuracy. No API. No latency. $0.002 per classification. The tool was deleted.

The best tool is sometimes no tool at all.