# OpenRouter tool search keeps large function libraries out of the prompt

Functions marked defer_loading are searched for when a model needs them, rather than sending every definition on every turn. OpenRouter says tool search adds no extra charge.

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Source: OpenRouter · Published 9/24/2026, 09:28:35

OpenRouter’s [tool search](https://openrouter.ai/tool/tool-search) keeps large tool libraries out of the prompt. Marking functions defer_loading lets the model search for the ones it needs, instead of paying input tokens for every definition on every turn. OpenRouter says there is no extra charge.

Tags: OpenRouter, Tool search, Function calling

[View original post](https://x.com/OpenRouter/status/2103157620756668764)