The @font-face CSS at-rule allows you to define and use your own custom fonts, thus allowing you to extend the limited set of standard system fonts that are installed by default on a computer, and that browsers can access and use.

The @font-face rule allows for linking to fonts that are automatically fetched and activated when needed. This allows you to select a font that closely matches the design goals for a given page rather than limiting the font choice to a set of fonts available on a given platform.

The @font-face rule consists of the @font-face at-keyword followed by a block of font descriptor declarations.

@font-face {
    /* font-descriptor declarations */
}
                

The font descriptor declarations include information in a form similar to the property:value pair form, and that provide a description of the font face being defined. You can describe the font face’s font-family, font-variant, font-weight, font-stretch, font-style, source (src, which indicates the source of the font face that you’re fetching into the page), and unicode range.

An example of a @font-face declaration may look like this:

@font-face {
  font-family: "Graublau Web";
  src:  url("GraublauWeb.eot?") format("eot"), 
        url("GraublauWeb.woff") format("woff"), 
        url("GraublauWeb.ttf") format("truetype");
}
                

The font-family property specifies the font family name that you will be able to use throughout the document. For example:

body {
    font-family: "Grablau Web", sans-serif;
}
                

The src property specifies the source of the font that the browser will use to fetch the font from. It takes a list of comma-separated url() functions, each containing a URI of the font. This is usually a local set of file formats (see notes section below for more information), or a URI to a location that allows you to download the font from.

@font-face {
  font-family: Gentium;
  src: url(http://example.com/fonts/Gentium.woff);
}
                

Inside an @font-face, and in addition to the two main font descriptors font-family and src, you can specify more information about the font face in use. For example, if you want to define and use a font family that has different font variations and weights, you would define the different font faces like this:

@font-face {
  font-family: "Open Sans";
  font-style: normal;
  font-weight: 400;
  src: local("Open Sans"), local("OpenSans"), url(http://themes.googleusercontent.com/static/fonts/opensans/v8/cJZKeOuBrn4kERxqtaUH3T8E0i7KZn-EPnyo3HZu7kw.woff) format("woff");
}

@font-face {
  font-family: "Open Sans";
  font-style: normal;
  font-weight: 700;
  src: local("Open Sans Bold"), local("OpenSans-Bold"), url(http://themes.googleusercontent.com/static/fonts/opensans/v8/k3k702ZOKiLJc3WVjuplzHhCUOGz7vYGh680lGh-uXM.woff) format("woff");
}

@font-face {
  font-family: "Open Sans";
  font-style: italic;
  font-weight: 400;
  src: local("Open Sans Italic"), local("OpenSans-Italic"), url(http://themes.googleusercontent.com/static/fonts/opensans/v8/xjAJXh38I15wypJXxuGMBobN6UDyHWBl620a-IRfuBk.woff) format("woff");
}

@font-face {
  font-family: "Open Sans";
  font-style: italic;
  font-weight: 700;
  src: local("Open Sans Bold Italic"), local("OpenSans-BoldItalic"), url(http://themes.googleusercontent.com/static/fonts/opensans/v8/PRmiXeptR36kaC0GEAetxjqR_3kx9_hJXbbyU8S6IN0.woff) format("woff");
}
                

The above example sets the font style and weight for every individual face; this makes it possible to use the font in its different styles and weight throughout the page:

h1 {
    font: 700 italic "Open Sans", sans-serif;
}

p {
    font-family: "Open Sans", sans-serif;
}

p .note {
    font-style: italic;
}
                

Also, the local function indicates that the user’s local copy of “Open Sans” is used; if the user does not have that font installed (two different names are tried), then the downloadable font (http://themes.googleusercontent.com/static/fonts/opensans/v8/cJZKeOuBrn4kERxqtaUH3T8E0i7KZn-EPnyo3HZu7kw.woff) is used instead.

All the font faces will load and be displayed because they are defined in the @font-face rules above. If you use a font face weight or style that is not defined in the @font-face, the browser will create its own version, which is almost always not desirable.

A given set of @font-face rules define a set of fonts available for use within the documents that contain these rules. Defined fonts are only available to documents that reference them. When font matching is done, fonts defined using these rules are considered before other available fonts on a system.

Trivia & Notes

Font Face Formats

The @font-face rule has good browser support, but different browsers want you to use different font file types. There are four main font formats used:

• WOFF (the Web Open Font Format): A web font format developed by Mozilla. According to the spec this format was designed to provide lightweight, easy-to-implement compression of font data, suitable for use with CSS @font-face rules. Any properly licensed TrueType/OpenType/Open Font Format file can be packaged in WOFF format for Web use. The WOFF format is not intended to replace other formats such as TrueType/OpenType/Open Font Format or SVG fonts, but provides an alternative solution for use cases where these formats may be less optimal, or where licensing considerations make their use less acceptable. The WOFF format also allows additional metadata to be attached to the file; this can be used by font designers or vendors to include licensing or other information, beyond that present in the original font. Such metadata does not affect the rendering of the font in any way, but may be displayed to the user on request. This format seems to be the best of all formats and seems to be the one all browsers are headed towards.
• EOT (the Embedded Open Type): It was developed by Microsoft. According to the spec: it was developed to enable TrueType and OpenType fonts to be linked to web pages for download to render the web page with the font the author desired. It’s the only format that IE8 and below will recognize when using @font-face.
• OTF/TTF (OpenType Font and TrueType Font): OpenType is a cross-platform type format that includes expert layout features to provide richer linguistic support and advanced typographic control. OTF is a more recent format than TTF, so OTF has some features that TTF doesn’t. These two formats can easily be copied and used illegally. The WOFF format is intended to be used as an alternative solution for use cases where these formats may be less optimal, or where licensing considerations make their use less acceptable, as mentioned above.
• SVG/SVGZ (Scalable Vector Graphics): SVG is a vector re-creation of the font. It was not meant to concur with other formats like PostScript or OTF, but as a simple means of embedding glyph information for rendering engines. SVG fonts usually have smaller file sizes, thus allowing for better performance on mobile devices.

Browser support for the different format differs, so you will most likely find all font formats linked inside an @font-face rule in the src descriptor. However, there is no need to do that anymore. Paul Irish has written an excellent article about a bulletproof @font-face syntax that is sure to work cross-browser, and that syntax is the one we will be using throughout the examples in the entry. You can read more about the why’s of the syntax in his detailed article.

You can also always refer to a font face kit generator to generate the @font-face rules for you. Read the “Tools” section below for more information.

Font Services

There are several web font services online that provide a long list of web fonts that are so versatile that you’ll definitely find a great font to match your design needs. These services provide access to legal fonts, and deal with the font delivery for you. Among these services we mention the following popular ones:

• Google Web Fonts
• Adobe’s Typekit
• FontSquirrel
• Fonts.com
• Font Deck
• Cloud Typography

If you want a quick overview of these font embedding services and a comparison between them, this comparative article on Smashing Magazine is an excellent starting point.

@font-face Generator

FontSquirrel’s generator is an indispensable tool when implementing @font-face.

Some of the font services above allow you to download a font as one format, not as a complete font kit. A font kit would contain all font formats you need including woff, eot, svg, and ttf. For example, you can download a free font from FontSquirrel itself, but the downloaded font usually only comes in one format (mostly ttf or otf).

Using the FontSquirrel’s generator you can upload that one font format and, as long as the font is legally eligible for web embedding, it will generate a complete font face kit for you to download, with a demo page and a style sheet that allows you to copy-paste the @font-face rules into your own style sheet and start using them directly.

You can learn more about creating a complete @font-face kit in one of these resources:

• @font-face embedding made simple with Font Squirrel
• Make Your Own @font-face Web Font Kits

@font-face Performance and Bugs

Rendering fonts on a web page differs from one browser to another. As mentioned on MDN, When Gecko displays a page that uses web fonts, it initially displays text using the best CSS fallback font available on the user’s computer while it waits for the web font to finish downloading. As each web font finishes downloading, Gecko updates the text that uses that font. This allows the user to read the text on the page more quickly.

There are also some performance issues resulting from loading custom fonts using @font-face because, after all, you will be loading additional large resources to your page, and that usually comes with a cost. Steve Souders has written a long and extensive article about the performance issues. There are also some useful tips for optimizing web font rendering, that you may be interested in checking out.