Tool-Use on René Zander | AI Automation Consultant

Claude API Tool Use: Function Calling Guide for Production

Thu, 26 Mar 2026 07:00:00 +0100

Tool use is the default pattern for any Claude workload beyond chat. If you are building anything that reads from a database, hits an API, writes a file, or decides between branches of logic, you should be using tools. If you are not, you are probably over-prompting and under-engineering.

I run ten Claude-powered agents in production as bash scripts on a Debian VPS. Every one of them uses tool use, not prompt chaining, to decide what to do next. The model picks a tool, I execute it, I feed the result back, the model continues. That loop is boring, predictable, and debuggable. It beats “parse the JSON out of the model’s free-form answer” every time.

Claude API Structured Output: Three Patterns for Guaranteed JSON

Wed, 25 Mar 2026 09:00:00 +0100

If you come from the OpenAI SDK, you are used to response_format: { type: "json_object" } or strict JSON schema mode. You pass a schema, OpenAI enforces it at the decoder level, you get parseable JSON or an error. Simple.

Claude does not have that. There is no response_format flag, no strict schema decoder, no JSON mode toggle. If you ask Claude nicely for JSON in the prompt, it will usually comply. “Usually” is not a word I want in production. I run ten AI agents as cron scripts on a Debian VPS. Every one of them parses Claude output into typed objects downstream. One unescaped quote in a string field will take down the pipeline at 06:30 while I am asleep.