Comment by jonahx

Prior art:

1. Plant UML: http://www.plantuml.com/plantuml/umla/SoWkIImgAStDuNBCoKnELT...

PlantUML supports many diagram types, and there's a nice VS Code plugin with side by side live preview.

2. https://www.websequencediagrams.com/

Has a hand-drawn style option which is nice:

https://i.imgur.com/lh4jaVL.png