{
  "id": "tool-search",
  "code": "PTL-0222",
  "term": "Tool Search",
  "aliases": [
    "deferred tool loading",
    "tool discovery"
  ],
  "category": "retrieval-tools",
  "definition": "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.",
  "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.",
  "example": null,
  "broader": [
    "function-calling"
  ],
  "narrower": [],
  "related": [
    "model-context-protocol",
    "context-engineering",
    "programmatic-tool-calling",
    "agent-skills"
  ],
  "introduced": 2025,
  "added": "2026-10-20",
  "sources": [
    {
      "title": "Tool search tool",
      "authors": "Anthropic",
      "year": 2025,
      "url": "https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-search-tool"
    },
    {
      "title": "Introducing advanced tool use on the Claude Developer Platform",
      "authors": "Anthropic",
      "year": 2025,
      "url": "https://www.anthropic.com/engineering/advanced-tool-use"
    },
    {
      "title": "Tool search",
      "authors": "OpenAI",
      "year": 2026,
      "url": "https://developers.openai.com/api/docs/guides/tools-tool-search"
    }
  ],
  "url": "https://protologue.com/t/tool-search/",
  "citation": "Protologue. (2026). Tool Search. In Protologue: A Taxonomy of Prompting and LLM Techniques (v1.4.0, PTL-0222). https://protologue.com/t/tool-search/"
}