Most advice about MCP server design says keep the tool count small. I read 91 sources: 38 say design fewer tools, 20 give a number (mostly 10–20), and only 10 measured tool count against accuracy at all. Then I measured it: 1,932 runs, three clients, 5 to 100 tools. On today's top models accuracy didn't move, not with 100 tools, not with look-alikes, not even with vague names. What moves is cost, and how much depends on how your client loads tools, not on the model. Since 2026 all three clients ...