I could create a URL that you could send an HTTP POST request to, with the PlantUML markup for your diagram in plain text (not deflated), and return to you the diagram image in the response. You would still need to know how to programatically send a POST request with the PlantUML markup text in the body of the request.
I am using MATLAB and it promises to be able to sent HTTP POST request according to the documentation.
If you are not a programmer, then this is probably too much for you to do on your side. This would be pretty simple for me to do my part on the server side. I will plan on doing it if you think it would be helpful.
Indeed, I am not a programmer. I do scientific computing, but have no background in web stuffs. As mentioned in my other post, I could make it work with installing graphviz and using the plantuml jar file. But my MATLAB code should work on Windows too and I want to avoid that the end user has to install additional programs. That is why I would like to solve the whole conversion (sending uml diagram in text file, perform the conversion through PlantText and download the SVG file) without installation.