Swimlanes.io – generated editable sequence diagrams

I use https://sequencediagram.org/ quite frequently these days, I like how you can get a link with the actual diagram encoded in it, makes it trivial to store and share.

Sequence diagrams seem like the go--to format for displaying data flow in a microservice-type environment, but even though there is a plethora of implementations in various languages and technologies that generate diagrams of this kind, they all lack certain functionalities, number one being the support for threads. Some solutions do provide the "par" fragment, but this is inadequate when message ordering corresponds to cronological ordering. Numbering messages may help, but I find it easier to grasp what is going on visually with multiple activations per lifeline (the best implementation of this I've found to date is the Quick Sequence Diagram Editor [http://sdedit.sourceforge.net/], but that project doesn't seem to be active or maintained).

I've recently tried to find a suitable solution for this on StackOverflow, but I've been rejected under the "Opinionated question" remark (::sigh::), so I could just as well do it here.

Is there a (Java based) sequence diagram generating tool/library that has the following functionalities:

. supports multiple threads and thread referencing in messages (multiple activations per lifeline)

. supports delayed messages (message trasmission and message reception can occur at different times, i.e. sending a message does not imply immediate reception on the other side)

. no custom language/pseudocode as input, but builder-style approach (I use Java to generate a text description of the diagram and then pass it to the library for parsing - I could just call the methods the parser calls and remove the unneccesary middle man)

. highly customizable visual style (PlantUML, the most flexible I've found in this regard, is notoriously bad at styling, mostly due to a lack of a coherent styling paradigm)

If not, how many people would be interested in such a thing? I may start it as an open source project myself...

FWIW, https://diagrams.net/ also have a downloadable version. But it's a point and click WYSIWYG editor, not a text notation like swimlanes.io.

I would really like a sequence diagram that allow for diagonal arrows, not just horizontal ones. A message takes time to arrive to its destination and sometimes it's interesting what else could happen during this time, for example the backend sending another response to the requester. Also requests don't arrive to the destination in the exact order they where made. All of these are impossible to represent with horizontal arrows.

I've been using this for years. Is really good and the best feature is that diagrams don't look like crap by default, which is not the case for most code to diagram tools out there. Looking at your Plant UML.