System prompt vs tool schema

Should the system prompt describe each tool?

No. The model already gets tools as their own field: name, description, JSON schema. Reprinting that list in the system prompt just costs tokens and goes stale.

Use the split:

• Tool description — what it does, how to call it, when this tool applies or must not.
• System prompt — who wins, what order, what never happens. Policy, not a catalog.
• Code / middleware — hard stops the model will skip if you only write them in prose.

If a tool never appears in the prompt and still gets called, that is working as designed.