The plugin lets you add tags by typing # and selecting a tag from the popup window.
It works but has some issues:
Demo
The repo is here: GitHub - roman-r-m/joplin-inline-tags-plugin
I'll publish it to npm later.
Just published a new version (0.0.2) to the repo.
There's one known issue - the list of tags will contain all available tags including those that the note already has. It's blocked by Plugin API: get notes/<id>/tags ignores the fields parameter · Issue #4407 · laurent22/joplin · GitHub
This is great! I've been wanting this for forever.
One thing I noticed is that if you tab to auto complete, it keeps the letters you already typed so #te--> [tab] --> #testte vs #test.
I'll take a look, thanks. Didn't realise tab also works for completing.
I've just published a new version 0.0.4 that has this issue fixed. Plus it will no longer suggest any tags the note already has.
Works great! Thanks!
Thanks for your work, @roman_r_m !
I have a suggestion to be able to keep the writing flow.
I find it a bit inconvenient to select this "Create new Tag" though, it disrupts the writing flow a bit. Is it possible to have the tags created automatically without asking? And if the tags are already assigned then just ignore them.
If a mistake is made by the user, like a spelling mistake or something like that, the user can take care of fixing it by himself.
(FR: Automatically create tags · Issue #1 · roman-r-m/joplin-inline-tags-plugin · GitHub)
I noticed that you can just hit tab once you are done writing and it will create the tag if it doesn't exist.
Is there a place to get the .jpl to install this, or do I need to install Webpack, Yoeman, etc. and build it myself?
Hmm, I thought the whole point of publishing to npm was to avoid the need to download and install jpl manually.
But sure, I can build you the jpl.
If you're on the latest version of Joplin (v1.6.8) you can install this (and any other published plugin) under Tools -> Options -> Plugins and using the search box. The only need for manual installation is to get plugins that haven't been published yet.
I've the latest Version (1.6.8) running and just installed the plugin.
Is it necessary to activate the plugin? I tried it in a new and existing note, but after typing # there is no popup or so...
Thank you!
This plugin requires v1.7.x and above. It's a bug in v1.6.8 that allows installing plugins that aren't supported. You'll need to update to a pre-release version if you want to use this plugin.
Thank you!
I haven't seen the requirements for this plugin, sorry 
It's not your fault, it's a bug in the current version. This won't be an issue in the future!
Now with 1.7.11 is available - I can use the Plugin 
Thank you!
Would it be possible to select the existing tags on top instead of "Create new tag:"? After some time I'll normally select the existing tags and will not create new ones.
Thank you!
I guess it makes sense. I'll do it in the next version.
And it's done.
Thank you @roman_r_m!
Have you pushed it to npm as well? Then I can try to use the internal update function of Joplin too 
I have, but it might take some time before it appears in Joplin.