Enable the Tool Search Tool to defer MCP schemas — 79.5%→88.1% selection accuracy on Opus 4.5 and ~85% fewer tokens

Anthropic Engineering·high signal

Instead of front-loading every MCP tool definition (a 'tools tax' Anthropic measures at 15k–60k tokens per turn, up to 134k before optimization), the Tool Search Tool exposes only a tool_search/tool_describe/tool_call bridge and loads each schema on demand. Anthropic's evals show selection accuracy rising from 79.5% to 88.1% on Opus 4.5 (and 49%→74% on Opus 4) while cutting tool-definition tokens ~85%. For builders running many MCP servers, flip this on before adding more tools — your bottleneck is schema bloat, not model capability.