https://sequencediagram.org/ is the best sequence diagram tool like that. It does diagram-to-text to if you draw a line etc with mouse. Can right click and have context options too.
That looks nice but it's a shame that it uses its own proprietary language (not PlatUML or MermaidJS) and the code isn't even available. So if you use it then you have to cross your fingers that the website continues to be available otherwise your diagrams will suddenly become unmaintainable.