Tools - Online XSLT debugger AKA jsfiddle for xslt

If you need a quick way to write/debug XSLT online I recommend this tool:

http://www.xsltcake.com/

Basically it's http://jsfiddle.net but for XSL. You get a similar layout with four tiled windows so that you can view everything on a single page. There is a pane for XML, a pane for XSLT and a pane for results (and one for parser errors).

This tool comes in handy to quickly query information in an XML document. Especially when you don't have access to any desktop tools for debugging XSLT.

For example you could use this generic XSLT to count the occurrences of each XML element in a given XML document: