Embedded OpenType (.eot)

The EOT file extension, Embedded OpenType, is a font format developed by Microsoft for embedding fonts in web pages. Introduced in the late 1990s, EOT addresses the need for a compact and efficient way to include custom fonts in web content while protecting font copyrights. EOT files are compressed versions of OpenType fonts, which can include both TrueType and PostScript outlines. Compression is achieved through subsetting, which includes only the characters needed for the web page, and LZ compression, developed by Agfa's MicroType Express. This results in smaller file sizes, crucial for faster web page loading times. EOT files are created using Microsoft's Web Embedding Fonts Tool (WEFT), which scans HTML documents and TrueType font files to generate the necessary EOT files. These files are then linked to web pages, ensuring that users see the intended fonts when viewing the page in Internet Explorer.

A key feature of EOT is its ability to protect font copyrights. By embedding fonts directly into web pages, EOT prevents unauthorized copying and distribution of font files. This is achieved through several mechanisms, including encryption and the use of a "trusted roots" list, which ensures that only authorized web pages can use the embedded fonts. Additionally, EOT files can include a root string specifying the domains allowed to use the font. If a web page tries to use an EOT file without the correct root string, the font will not be displayed. Despite its advantages, EOT has limitations. It is primarily supported by Internet Explorer and is not widely adopted by other browsers. As a result, the Web Open Font Format (WOFF) has become the preferred choice for web fonts in recent years. However, EOT remains an important part of web font history and is still used in some legacy systems.