STL-Viewer STL Files: STL (an abbreviation of “stereolithography”) is a file format native to the stereolithography CAD software. Nowadays STL files are widley used within 3D-Printing technology. Please note: This project is currently flagged as experimental. The viewer is implemented as a web-application which emulates a local web-server. Known Problem so far: The application has a memory limit, which might be reached quite soon. In other words: when trying to view STL-files bigger than appr.