All diagrams' sources are stored in .drawio.svg files — SVG files with embedded Diagrams.net content. They are made using Diagrams.net (formerly Draw.io).
The recommended way to edit these files locally is with Visual Studio Code's Draw.io integration.
If you want to use Diagram.net's web app instead of the Visual Studio Code integration, then be sure to save it by exporting the diagram as SVG, using the following settings:
- Zoom: 110%
- Border width: 12
- Check: Transparent Background
- Uncheck: Include a copy of my diagram