Tool Design & MCP

Key idea: A model chooses a tool only from its name and description, and every tool you connect is sent with every request. Clear descriptions get the right tool called; extra tools cost tokens even when they don't help.

Right tool vs. tokens per request

Clear · 4 toolsClear · 20 toolsVague · 4 toolsVague · 20 tools
0/124/128/1212/1207671,5332,300Input tokens per requestRun a setup to plot it here
  1. Run Clear with 4 tools. Does the model ever pick the wrong one?
  2. Switch to Vague. The tools do exactly the same jobs. Which ones does the model now pile onto, and why?
  3. Run Clear with 20 tools. Accuracy holds, but look at the input tokens per request. What are you paying for?
  4. Run Vague with 20 tools. What happens when names are vague and there are look-alikes to choose from?
  5. If you were connecting three MCP servers to your product, what would you check before shipping?
Tool listnames + descriptionsRequest12 support questionsModelpicks one toolministral-8bTool callwhich tool it choseCheckerthe right tool?Scorecardright picks, tokens
Press Run to watch it run

Results

Run the requests to see which tool each one went to.

Behind the scenes

Run it and every request, the tool the model picked, and its token cost will show up here.