I stumbled onto this pattern while building agents with Deep Agents, watching a tool registry grow past the point where sending every schema on every turn still made sense. What follows is the pattern itself, stripped down so it drops into any tool-calling agent loop today regardless of framework, backed by a benchmark against a synthetic 61-tool registry.The Problem: Tool Count Grows, Relevance Per Turn Doesn'tMost agent frameworks assemble the tool list once at construction time and send the whole thing to the model on every call, regardless of what that turn is about. Fine at 5-10 tools. Once you wire up a handful of MCP servers (Slack, GitHub, Linear, a calendar, a CRM, each contributing 3-6 schemas), every turn starts carrying 40-60 tool definitions whether the user asked about a Slack message or not.