A plan-check letter is the city telling you, four to eight weeks after you applied, what it would have told you on day one had anyone looked. This tool looks on day one.
Upload the set you are about to submit — drawings, calcs, reports, forms. It reads them the way the plans examiner will: against the jurisdiction's own submittal requirements, its municipal amendments and the code edition it has actually adopted. What comes back is a report in the shape you already know from a correction letter, one finding per row, each pointing at the sheet and the section behind it — before a reviewer has written a single comment.
It is in build now. Leave an email and you will have it the day it opens.