MCP
Tool Search
A Claude API tool that lets the model discover and load tool definitions on demand instead of having every tool's schema in its context window from the start.
In depth
A Claude API tool that lets the model discover and load tool definitions on demand instead of having every tool's schema in its context window from the start. You mark tools with defer_loading: true, and Claude searches the catalog by name and description, using either regex or BM25 variants, then loads only the few it needs. Anthropic reports this typically cuts tool-definition tokens by over 85 percent and keeps selection accuracy high, which otherwise degrades past 30 to 50 tools. It is especially useful for agents connected to many MCP servers.
Primary source: platform.claude.com
Example
In practice, developers reach for Tool Search when they need the capability described above as part of an AI feature or workflow.
Go deeper at Developers Digest
Hands-on guides, comparisons, and tutorials that cover MCP.
FAQ
Common questions
What is Tool Search?
A Claude API tool that lets the model discover and load tool definitions on demand instead of having every tool's schema in its context window from the start.
Why does Tool Search matter for AI developers?
Tool Search sits in the MCP part of the AI stack. Understanding it helps you make better decisions when building, debugging, and shipping AI features.
Where can I learn more about Tool Search?
Developers Digest publishes tutorials and videos that cover MCP topics including Tool Search. Check the blog and YouTube channel for hands-on walkthroughs.
Related
Related terms
MCP
MCP Tool Poisoning
MCP tool poisoning is an attack where a malicious MCP server hides instructions in a tool's description, which the model reads but the user usually never sees.
MCP
MCP Client
An application that connects to MCP servers to use the tools, resources, and prompts they expose.
MCP
MCP Tool
A function exposed by an MCP server that an AI agent can call to perform an action.
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