This month’s Cool Tool post goes to FFFFallback, a handy little bookmarklet that lets web designers easily test different fallback fonts for their web-based creations.

To install, simply drag the bookmarklet to your browser’s toolbar (only works for browsers that use WebKit such as Chrome, Safari, and FireFox). To use, simply click the bookmarklet and it will scan the current web page’s CSS for existing Web Fonts and list them on the right side of your browser along with input fields for changing the fonts and font styles (e.g. font-size, color, line-spacing).

FFFFallback was created by two self-proclaimed “professional nerds” Josh Brewer and Mark Christian who eke out a living at a little known company called Twitter. You can download the source code on github.

Looking for Web Fonts to fill out your @font-face tag, start with Google’s open-source fonts (with over 400 fonts). If you don’t mind paying a monthly fee for fonts then try Adobe’s Typekit (with over 700 fonts). There is a free plan under Typekit but you only have access to a “trial library”  (at last count 192 fonts) and requires you to display the Typekit badge.