When a mechanical designer sends a revised STL to a client or print team, the most common response is, “It looks about the same.” But a smaller hole, a newly thin wall, or an added overhang can change assembly fit, print supports, and pricing. Those changes are difficult to spot by rotating two models separately. Users drop the before and after STL files into a browser and select the intended manufacturing method, such as FDM printing, resin printing, or machining. The page overlays the models, colors added and removed material, and groups differences into practical issues such as hole diameter, wall thickness, mating faces, and overhang areas. Selecting a difference shows its dimensions, a recommended viewing angle, and its potential manufacturing impact in a side panel. Users can mark key areas and generate a link with a fixed view and dimensional callouts, so clients can confirm changes in the browser without installing CAD software. Once the review is complete, the link summarizes what has been confirmed, what needs revision, and what remains disputed. By default, models are compared locally in the browser, which suits parts that have not yet been made public or are covered by an NDA. The first release focuses on STL geometry differences and print risks; it does not replace full CAD constraint checking or provide a factory’s final quote.