Stage 2 · Lesson 1 of 7
Defining tools
A has three parts: a name, a description and a for its arguments. JSON Schema is a standard way to describe the shape of JSON, listing each field, its type and which fields are required. You send the definitions with every request, and they are all the model knows about your tools.
Anthropic calls the schema input_schema and OpenAI calls it parameters, but the idea is the same. Give each tool one clear job, a name that says the action, such as search_orders, and a few typed arguments. Use enums (fixed lists of allowed values) for choices such as order status.
Common trapone vague tool such as query(text) that does five jobs, which the model will call at the wrong time with the wrong arguments.
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Resources for this stage
Start with· follow one of these
- GuideFreeClaude Tool Use Documentation
Anthropic · Intermediate
Read Overview, Define tools and Handle tool calls, then follow the tutorial that grows one call into a full loop
- GuideFreeOpenAI Function Calling Guide
OpenAI · Intermediate
The same loop on the Responses API: read it after your first provider to see what is universal