While this is pretty cool, I like these alternative web-based services listed below a lot better because they are easier to use:

http://www.gliffy.com

http://www.lovelycharts.com

*i'm not affiliated with them in any way.

Or -ahem- http://www.dabbleboard.com

*am affiliated

I am also a big fan of gliffy. I'll give dabbleboard a shot, though.

No WYSIWYG editor? I'm not about to learn another markup language to write UML, which is itself a markup language.

As someone who creates a lot of diagrams, I disagree. Most diagramming tools require me to spend 80% of my effort on layout issues to make diagrams look good. I would much rather have a mini language in which I can express my diagram than fumble around with pixels.

Doing things in text also keeps the diagrams Wiki friendly, which might be a consideration (it sure is for me), allows easy auto-generation, and so on.

I've been looking for a good tool in this area. Groff has PIC, which was created by Kernighan and sort of does this (this is what W. Richard Stevens used in his books, for example), but I want pretty colors and gradients and rainbows. I'd love to hear suggestions for tools in this area.

I am thinking about writing my own tool, maybe in JavaScript to use a familiar syntax and allow a sort of eval loop on the browser.

The idea is that you can do things like this:

    <img src="http://yuml.me/diagram/class/[User|+Forename+;Surname;+HashedPassword;-Salt|+Login();+Logout()]"/>

There is some advantage to having a text-based markup language. That way you can emit it from tools.

If you are modeling in text (which is a good thing) why not use something like alloy (http://alloy.mit.edu/) which is far more expressive and can be analyzed and checked automatically.

Very cool! But don't make me WRITE code to create something visual. Let me draw it, then give me the code to make it easy to embed.

While I haven't really used this particular service, I disagree with your general premise.

I love graphviz, for example. Graphviz is actually quite awesome. I can draw dependency graphs, or any other kind of graph, without touching the mouse. I don't have to care about the layout, and I don't want to, since I'm no designer. Actually I'm quite bad at layouting stuff - and the algorithm gets it right most of the time.

I can quickly change things, insert or delete an element, without having to worry about re-layouting everything myself. So, cut a long story short: doing visual tasks text-based is not a bad thing per se.

Again, I haven't really given this thing a try for long enough, but right now, the text-based interface seems OK for me. But maybe that's just me, being a very text-driven person.

For online uml sequence diagrams : http://www.websequencediagrams.com/ . Too bad that's not open source and no vector export format.

The "Draw Diagram" tools need drawing tools...

I guess it should be called "Render Diagram".

Not if you view it as an API.

I find it non-obvious that a newline isn't an acceptable delimiter between relationships, and I need to also include a comma at EOL.

Can you include url links in the diagrams?

This is pretty cool. Good job.