Great paper from Microsoft Research and colleagues. If you auto-generate MCP tools from agent trajectories, this one is worth your time. AutoTailor turns web trajectories into parameterized browser-automation APIs and then filters them. A quality filter drops APIs with the wrong granularity or duplicate function, and a usage filter keeps the ones likely to be needed. That takes 1,283 candidates down to 87. Online, it watches task outcomes, adds APIs for recurring gaps and prunes ones that go unused, ending at 33. On 106 WebArena Postmill tasks, the 33 APIs with a ReAct fallback reach 90.6% correctness against 87.5% for ReAct alone. Request-token cost drops 57.8% and latency 29.4%. Without the fallback, accuracy matches the unfiltered set while using 94.9% fewer request tokens. Paper: