Tools to help with CSS coding

CSS tools to check the validity, integrity, quality of CSS code and to make CSS tasks easier.

validation
optimization
layout tools
development tools

css validation
Jigsaw.w3.org - W3C CSS Validation Service
An essential tool for all web developers. Validate your web pages using the W3C CSS Validation tool.
Websitedev.de - W3C CSS Validation FAQ
An FAQ for the W3C CSS Validation Service
Htmlhelp.com - CSS check
Enter a URL or some CSS code to have the code checked.
css optimizing
Immike.net - CSS redundancy checker
Online tool to search through your CSS and find CSS selectors that aren't used by any of your HTML files and may be redundant.
Cleancss.com - CSS Cleanup Service
CSS formatter and optimizer. This online application which will clean up your CSS.
No-ip.org - CSS Compressor
CSS formatter and optimizer. Another online application which will clean up your CSS.
Lonniebest.com - Format CSS online
Add valid CSS into an online form and choose from a number of formatting options.
css layout tools
Positioniseverything.net - ClevaTreva pagemaker
ClevaTreva and the folks at Positioningiseverything have created a CSS layout generation tool. CSS Source Ordered 1-3 Columned Page Maker. It lets people customize a cross-browser layout and has features for experienced CSS designers.
Theboxoffice.be - text around images
The Box Office lets you wrap/float/contour text around freeform images using CSS for usage in (X)HTML pages.
css development tools
SelectORacle - CSS to english translator
Can elucidate on some CSS script by translating the commands into an English description.
Themaninblue.com - EM widths
A page to show how EM widths change depending on font size.