UTF-16

UTF-16 (<a href="/facts/16-bit_computing/bTGS44Ne">16-bit</a> <a href="/facts/Unicode/DDu3MfPV">Unicode</a> Transformation Format) is a <a href="/facts/Character_encoding/ShJHIMoA">character encoding</a> that supports all 1,112,064 valid <a href="/facts/Code_point/R184ugJX">code points</a> of Unicode. The encoding is <a href="/facts/Variable-width_encoding/2LygbAV6">variable-length</a> as code points are encoded with one or two 16-bit code units. UTF-16 arose from an earlier obsolete fixed-width 16-bit encoding now known as UCS-2 (for 2-byte Universal Character Set), once it became clear that more than 216 (65,536) code points were needed, including most emoji and important <a href="/facts/CJK_characters/TGz9tR4C">CJK characters</a> such as for personal and place names.
UTF-16 is used by the <a href="/facts/Windows_API/RRw4RtTu">Windows API</a>, and by many programming environments such as <a href="/facts/Java_programming_language/9ScgFyAL">Java</a> and <a href="/facts/Qt_(software)/gVhwlQnJ">Qt</a>. The variable length character of UTF-16, combined with the fact that most characters are not variable length (so variable length is rarely tested), has led to many bugs in software, including in Windows itself.
UTF-16 is the only encoding (still) allowed on the web that is incompatible with 8-bit <a href="/facts/ASCII/vGUI33Qu">ASCII</a>. However it has never gained popularity on the web, where it is declared by under 0.004% of public web pages (and even then, the web pages are most likely also using <a href="/facts/UTF-8/xlaVHSyf">UTF-8</a>). UTF-8, by comparison, gained dominance years ago and accounted for 99% of all web pages by 2025. The <a href="/facts/WHATWG/WoyKwRJR">Web Hypertext Application Technology Working Group (WHATWG)</a> considers UTF-8 "the mandatory encoding for all [text]" and that for security reasons browser applications should not use UTF-16.

UTF-16 open-in-new

UTF-16