Tools and Tool Use: The Contract Between Model and World

What a tool looks like from the model’s side of the glass, why the name–description–schema contract is the only documentation the model ever reads, and how tool and result design decide whether your agent works.

Content current as of 2026-09.

Lessons

  1. The tool contract
  2. Designing tools models can actually use
  3. Results the model can act on
  4. How many tools is too many?
  5. Diagnose the failure