Oh shit! Lock up your daughters it's ...

███████╗██╗     ██╗   ██╗███╗   ███╗██╗      ██████╗ ██████╗ ██████╗ 
██╔════╝██║     ██║   ██║████╗ ████║██║     ██╔═══██╗██╔══██╗██╔══██╗
███████╗██║     ██║   ██║██╔████╔██║██║     ██║   ██║██████╔╝██║  ██║
╚════██║██║     ██║   ██║██║╚██╔╝██║██║     ██║   ██║██╔══██╗██║  ██║
███████║███████╗╚██████╔╝██║ ╚═╝ ██║███████╗╚██████╔╝██║  ██║██████╔╝
╚══════╝╚══════╝ ╚═════╝ ╚═╝     ╚═╝╚══════╝ ╚═════╝ ╚═╝  ╚═╝╚═════╝ 

Slumlord is built atop the wang-hardeningly awesome plantuml. It gives you a "live preview" of your UML diagrams when you save.

First you need Java installed.

Then, install this plugin with your favourite vim plugin manager.

For vundle, just stick this in your vimrc and smoke it:

Plugin 'scrooloose/vim-slumlord'

Then run :Vundle install

I also recommend installing the plantuml-syntax plugin as Slumlord uses this for its syntax file.

Plugin 'aklt/plantuml-syntax'

Edit a .uml file and enter some plantuml code. When you save it, a preview will be forcefully inserted/updated at the top of your file!

Note: I have only used this for sequence diagrams - the ASCII output of plantuml seems to be less than stellar for other diagram types.