Markdeep[0] from Casual Effects has a way of drawing diagrams using extended markdown.

I used it to write this document with two diagrams: https://loan-free-ed.neocities.org

Other tool I like are PlanetUML[1], BoUML[2] and Modellio[3](it is very heavy though on system resources!)

[0] https://casual-effects.com/markdeep

[1] https://plantuml.com

[2] https://bouml.fr

[3] https://www.modelio.org