I have used a tool that ran as a client application. It allowed for most UML Diagrams. It saved these diagrams as HTML/SVG. I cannot remember the name of the tool. So I am reaching out to the hive mind to see if anyone else remembers this tool (or is using it now).
Try digging for alternatives on draw.io her. It might be draw.io, i know it saves in either XML or HTML format, not necessarily sure about the .SVG though
I found a diagram that I had made with the tool. Looking at the source I was able to find the product name. It was referenced in a comment in the source. It is called violet and can be found here: https://sourceforge.net/projects/violet/ Unfortunately, it appears to be a dead project. Too bad I like the fact that it is lightweight and consumers of your diagrams need nothing beyond a fairly current browser.