# Tool Search

> Tool search is an agent capability in which tool definitions are not all loaded into the model's context up front, and the model instead searches a tool catalog and loads only the definitions it needs for the current task.

- Identifier: PTL-0222
- Category: Retrieval & Tool Use
- Canonical URL: https://protologue.com/t/tool-search/
- Also known as: deferred tool loading, tool discovery
- Introduced: 2025

## Description

Large sets of tools, such as those from several MCP servers, can use tens of thousands of tokens in definitions before any work begins, and models choose tools less accurately as the number of available tools grows. With tool search, developers mark tools as deferred and the model retrieves matching definitions by keyword, pattern or natural-language query. Anthropic and OpenAI both offer it in their APIs.

## Broader terms

- [Function Calling](https://protologue.com/t/function-calling/)

## Related terms

- [Model Context Protocol](https://protologue.com/t/model-context-protocol/)
- [Context Engineering](https://protologue.com/t/context-engineering/)
- [Programmatic Tool Calling](https://protologue.com/t/programmatic-tool-calling/)
- [Agent Skills](https://protologue.com/t/agent-skills/)

## Sources

- Anthropic (2025). Tool search tool. https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-search-tool
- Anthropic (2025). Introducing advanced tool use on the Claude Developer Platform. https://www.anthropic.com/engineering/advanced-tool-use
- OpenAI (2026). Tool search. https://developers.openai.com/api/docs/guides/tools-tool-search

## Cite this entry

Protologue. (2026). Tool Search. In Protologue: A Taxonomy of Prompting and LLM Techniques (v1.4.0, PTL-0222). https://protologue.com/t/tool-search/

License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)