The code in the image did render alrright in the previous version of Joplin
Mermaid support is currently disabled unfortunately and is under review.
Now that you have added support for plugins, is it possible to add mermaid again? I kinda liked its functionality and with the new plugins option everyone could choose, whether he wants to activate it or not.
I’ve been trying to add it, but ran into a few issues. I believe I have to create custom rules to make it work and add the js to the viewer. I’ll try to work on it on the weekend again.
Note that while I’ll accept a PR for Mermaid, for now I won’t mention it to the doc or provide support for it (and I think support will be needed because it seems to be a bit buggy and it’s not clear if someone is still maintaining this lib).
Good to know, but I am not even sure, if I get it working...
This is actually a very good point. I think it should be mentioned in the FAQ and the README.md that you cannot maintain any of the plugins, because they are not your code (upstream) and that they are provided as is.
The issue is that although we can say we don’t maintain plugins, if they are buggy or cause problems in Joplin, it still looks that it is Joplin that doesn’t work properly. It basically gives the feeling of an unstable app.
So there’s a fine line here and Mermaid is a bit at the limit - a bit buggy but at the same time very popular. So I guess we can add it, and rather than not documenting it we’ll put a warning saying that integration is experimental, that we cannot support it, and certain things won’t work, etc.
Sounds good.
Ideally with a big, fat 
right where the plugin is turned on. (And make it off by default.)
Hi All,
Has there been any update on the position around Mermaid support?
I’m a heavy Mermaid user and am used to the level of support available in VS Code, but it is not suitable as a general purpose notetaking app. I’ve been using Joplin for a couple of months now and generally finding it a great replacement for Evernote and OneNote, but the lack of Mermaid diagram support is a sore point for me. Would really love to see this re-enabled in the product even if there were big warning signs next to it. This is one of the main points that keeps me looking at the Typora app to see how it is progressing.
Thanks, Matt
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Same here. I found mermaid very useful.
Thanks @tessus ! I can see you have started on this now.
Looks like progress has been paused on this since Nov 2019 (https://github.com/laurent22/joplin/issues/2001). Is there still interest in proceeding? If so, how can I help?
The problem is that the render code was moved out of the core code, so now it’s a bit more complicated to add it back. I did some changes locally and it was working fine, but now I have to figure out how to make it work again.