ModelRefs / Tool Router — Tool Pattern
Tool Router — Tool Pattern
Pre-filter a large tool catalog down to a few candidates per turn using semantic routing, then expose only those to the model.
Overview
When you have dozens or hundreds of tools, exposing all of them inflates prompts and degrades selection accuracy. A router embeds the user query, retrieves the top-N matching tools, and exposes only those.
When to use it: You have a large tool catalog and need to keep prompts small and selection accurate.
Pattern details
| Pattern class | workflow |
|---|---|
| Difficulty | advanced |
| Invocation mode | synchronous |
| Also known as | tool retrieval, dynamic tool selection |
| Last reviewed | 2026-06-07 |
Known failure modes
- Miss-route — The right tool falls outside top-N. Mitigation: Raise N; add reranker; allow fallback to full catalog.
When not to use it
- Exposing 200 tools to the model in one prompt.
Continue your research
Use these connected ModelRefs sections to compare alternatives, inspect implementation paths, and review the evidence and governance boundaries relevant to Tool Router — Tool Pattern.
Frequently asked questions
When should I use the Tool Router tool pattern?
You have a large tool catalog and need to keep prompts small and selection accurate.
What are common failure modes of Tool Router?
Miss-route
Is Tool Router production-ready?
Yes when paired with the safety controls and observability hooks documented on the pattern page.