Fast Fonts responds to the fast-font-selector: URL scheme, with the following options:

Option	Abbreviation	Parameters	Explanation
callback	cb	<URL>	URL scheme to call in order to return chosen font
magic		<text>	Arbitrary characters to pass back to caller with result
welcomeTitle	wt	<title>	Title to display in AlertView on launch
welcomeMessage	wm	<text>	Text to display in AlertView on launch
welcomeDismiss	wd	<label>	Button text used to dismiss AlertView
confirmChoiceText	ct	<label>	Text for confirmation button
fontFamilies	f	<family>[,family]*	Comma-separated list of font families to offer
fontNames	n	<name>[,name]*	Comma-separated list of font names to offer
fontSizes	sz	<size>[,size]*	Comma-separated list of font sizes to offer
fontVariants	var	<name>[,name]*	Comma-separated list of variants (e.g. Bold, Italic, BoldItalic) to offer
defaultFont	df	<font>	Font to initially select
defaultSize	ds	<size>	Size to initially select
displayText	txt	<text>	Text to display in lower screen area
readonly	ro	[boolean¦(readonly¦read)¦(readwrite¦write¦writable)]	Whether displayText can be modified
debug		[boolean¦(save¦keep)¦(clear¦unset)]	Whether to enable debug code and options

... where boolean is a value matching <(0¦off¦false)¦(1¦on¦true)>.

e.g. fast-font-selector:callback=<private scheme: or URL>;magic=test;welcomeTitle=Fast%20Fonts%20Test;welcomeMessage=API%20Test;welcomeDismiss=Continue;confirmChoiceText=Select%20This%20Font;displayText=Example%20text

When the button with title 'confirmChoiceText' is tapped in Fast Fonts, the calling application is called by the specified scheme with parameters 'font=' followed by the Font Name, 'size=' followed by the Font Size, 'text=' followed by the contents of the lower text-area (if not read-only), and 'magic' (if passed in originally).