+## Setting `fstl` as the Default STL Viewer
+
+### Windows
+
+1. Right-click an STL file
+2. Select `Open With` >>> `Choose another app`
+3. Select `More Apps` and `Look for another app on this PC`
+4. Enter the path to the `fstl` EXE file
+
+### MacOS
+
+1. Ctrl+click an STL file
+2. Select `Get Info`
+3. Navigate to the `Open with` section
+4. Select `fstl` in the dropdown
+5. Click `Change All`
+
+### Linux
+
+If `mimeopen` is available on your system, it can be used to set `fstl` as the default viewer for STL files.
+Run the following in your terminal:
+
+```bash
+# replace example.stl with an actual file
+mimeopen -d example.stl
+```
+
+The following output will result:
+
+```
+Please choose a default application for files of type model/stl
+
+ 1) Other...
+
+use application #
+```
+
+Select the `Other` option and type `fstl` as the desired command to open STL files.
+This will now become the system default, even when opening files from the file manager.
+