Perhaps I did an overall mistake in setting up the embed mode. I did follwing steps:
1) Downloading the complete
draw.io Project with all folders
2) loading it on a Server
3) setting up an url to the index.html in the war-file.
I did not build up anything or...? Is that right?
What i tried for testing a plugIn is this:
The file p1.js is placed in war/plugins (as it is in the github Project). The url i called from my application ist following one: '
http://192.168.(rest of my Ip-Adress)/drawio/index.html?https=0&proto=json&embed=1&splash=0&spin=1&local=1&plugins=1&p=p1';
If i call:
https://www.draw.io/?proto=json&splash=0&spin=1&local=1&plugins=1&p=p1 (Its same after ?, i just left embed=1 and https=0 away) the plugin is loaded properly.
I observed with the firefox developertool the debugging-Process and follwing parameters have been loaded.

Hope this helps. I got the feeling that i did something wrong in my overall way to set it up. If so, please let me know, than i will try to do it again.
Do you mean this documentation:
https://desk.draw.io/support/solutions/16000042316Thanks
Am Mittwoch, 8. März 2017 12:36:47 UTC+1 schrieb Gaudenz Alder:
Plugins work for me in embed-mode, you'd have to show us what you've tried in order to debug it. Does it work if you
www.draw.io? The documentation is constantly updated.