We developed A-SPEC, a computational design tool that aims to be a partner for architectural designers, based on the concept of "thinking together about RESTROOMS.” For any specified space, the cloud-based A-SPEC program will run multiple simulations and propose some better restroom-layout plans from tens of thousands of ideas. The design know-how that we’ve proposed in the past is utilized throughout the program to evaluate both the automatic calculations and the layout of the automatic design results derived from those calculations. The design results are converted into a 3D model using Forge Viewer, with veracity confirmable by the human eye. Finally, the results can be linked to Revit software and AutoCAD software via the Design Automation API. In addition to reducing design work time, this tool enables generalization and uniformity of design accuracy without relying on the individual know-how of designers.