Function calling guides

The recipe

Six steps for shipping reliable tool calling. Try each one in the workspace as you go.

1. 1Understand the loop
   What is function calling

   How the model, your tools and the tool-result turn fit together.

2. 2Design your tools
   Schema best practices

   Names, descriptions, types, enums and distractor tools that models get right.

   Paste them in the Tools editor
3. 3Write the system instruction
   System instruction

   Policies, defaults and scope: when to call, when to ask, when to answer directly.

4. 4Shape tool outputs
   Tool output

   Return success, errors, timeouts and large results in a way the model can use.

   Add a Tool result turn
5. 5Cover the call patterns
   Function call patterns

   Single, parallel, sequential and no-call cases, plus the tricky ones.

   Try them in the Arena
6. 6Pick a model and measure
   Evaluation

   Metrics and per-slice evaluation on held-out tools, before you commit to a model.

   Compare models blind