I write in LESS to start with. So I took the compiled CSS from less, then tried to run it through the css2less convertor, then recompile what it generates.
Few things I noticed.
 Selectors get rearranged
 Cannot correctly handle base64 images
 Cannot handle child selectors. ie :child / n-th child.
 Comments get mangled (confirmed from another commentor below)
 Generates duplicate properties (where the duplicates didn't exist in precompiled). Creating duplication properties is actually correct, such is the case where you would want duplicate background properties (to support IE/FF/Chrome gracefully etc). However, you don't want it to generate identical properties where the values are also the same.
 font-faces wrong. (To be fair, this is hard to get right even in normal LESS).
All constructive feedback. I'm still impressed that it did a fairly decent job.
* Correctly extract sets of compatibility (prefixed) properties into a mixin
* Extract and fix prefixed properties missing the unprefixed version and/or other prefixes
First thing, Css2less is hosted on our small server by home, so it's kind of hard to handle the amount of today visits :)
Please be patient if server goes down for a few minutes...!
Second thing, I see a lot of good ideas here ! You should definitely propose them on the Github page so it's not lost :
There's still a lot of work to accomplish as you expected it, so it's also the occasion for me to make a call for ruby gurus who could helps us to add this awesome features :
Thanks all guys for your feedback, much appreciated.
After that you can run for example :
css2less style.css > style.less
I've used that and it's quite a nice start, but you shouldn't really expect it to be as good as hand-written LESS or SASS. Lots of the wins of using a preprocessor is in defining good re-usable mixins and hierarchies, and a conversion tool simply can't give you all of that.
IMHO if you want to use SASS/LESS, write all of it from scratch.
Even without that, I'd have expected it to at least extract repeated color values into variables, and maybe repeated propsets into mixins.
Because really, from a short test it does little more than me changing my file's extension to .less/.scss
submitted 6 days ago
i also liked the linked one in this thread as well: http://css2sass.heroku.com/
Oh and if it declared variables for repeated values, I'd use it for sure.
edit: Just noticed it doesn't format prefixed properties neatly, lists properties in a weird order, and for whatever reason, the order of elements gets rearranged. That's a major issue... for some reason, my .container ended up at the very bottom.