WebFonts is a technology for automatically downloading and temporarily installing fonts on demand over the Web, for the display of content (HTML/CSS, SVG, MathML ...) without requiring the reader to separately download and install fonts to their operating system. Two things are needed, firstly a way to describe the characteristics of the font (including, but not limited to, its location on the Web) and secondly an actual font which may be downloaded for temporary use in accordance with it's license.
The second part has been implemented with multiple formats - EOT (in Microsoft Internet Explorer), CFF (in Adobe SVG Viewer), SVG fonts (in multiple SVG implementations), TrueType/OpenType (in Safari, Mozilla Firefox, and PrinceXML). What was lacking was a single, interoperable format which all implementations would use.
Current work in CSS3 Fonts is refining the CSS2 description (and removing some options described in CSS2 but not implemented, such as font synthesis); XSL 2.0 is also expected to use a similar mechanism.
In March 2010, a Web Fonts Working group was chartered to complete the set of specifications needed for interoperable Fonts on the Web. The main task of this group is to standardize Web Open Font Format (WOFF), a way of packaging OpenType or TrueType fonts for delivery over the Web. On 27 July 2010, the First Public Working Draft of the WOFF specification was published. This includes some corrections and clarifications based on feedback. An appendix gives some real-world examples of WOFF metadata, as used by foundries today. The WOFF specification moved to Candidate Recommendation in August 2011 and is now undergoing implementation testing.
Numerous SVG 1.1 implementations and SVGT 1.2 implementations implement WebFonts, using either the CSS or the XML syntax. All support SVG font format, some support other formats as well including Adobe CFF, OpenType, and WOFF.
Firefox, Opera, Safari and Prince XML support WebFonts using OpenType/TrueType format. Many Libre fonts are available in this format and may be freely used within the terms of their license. Firefox implements same-origin restrictions for font linking.
Over the last year, there has been substantial developer interest in WOFF. In September 2009, Jonathan Kew produced open-source sample code for conversion between sfnt (OpenType/TrueType) and WOFF. In October 2009, Mozilla Firefox added experimental WOFF support to their CVS base; that code has now undergone security review and in January 2010, Firefox 3.6 became the first production browser to ship with WOFF support.
In December 2009, Prince XML (a CSS print formatter for XML and HTML documents) added WOFF support. In April 2010, the Google Chrome browser added WOFF support. In February 2009, the font editor fontforge added WOFF support, so fonts can be directly exported as WOFF. In June 2010, the third preview release of Microsoft Internet Explorer 9 added WOFF support and in July 2010, Webkit added WOFF support as well.
Also, wofftools provides various tools including a WOFF validator, a WOFF inspector, and a utility to auto create CSS @font-face rules for a given WOFF font.
The choices are to host fonts yourself along with your other content, or to use a third party font hosting service.
Fonts in WOFF may be licensed from several commercial foundries, including FontShop (WebFont end user license), FontFont, Monotype/Linotype/ITC fonts from Fonts.com Webfonts and the Adobe Webfonts type library, as well as fonts from many other foundries, from TypeKit.
Libre fonts are intended to be free in both the monetary sense and the usage sense. The license for a given font should however be consulted; for example some licenses allow use with attribution, but prohibit modification (including conversion to other font formats). One source of Libre fonts is the Open Font Library. Most fonts there are under the SIL Open Font License, which permits use with attribution, and also modification (if the 'reserved font name' is changed). The OFL was recently clarified, conversion of an OFL-licensed OpenType or TrueType font to WOFF, without subsetting, is not a 'modification' and thus does not require renaming.