UTF-8

{{Short description|ASCII-compatible variable-width encoding of Unicode}} {{Infobox character encoding | name = UTF-8 | mime = | alias = | image = | caption = | standard = [https://www.unicode.org/versions/latest/ Unicode Standard] | status = | classification = Unicode Transformation Format, extended ASCII, variable-length encoding | encodes = ISO/IEC 10646 (Unicode) | extends = ASCII | prev = UTF-1 | next = }}

'''UTF-8''' is a character encoding standard used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode Transformation Format{{snd}} 8-bit''.<ref name=":1">{{Cite book | title = Unicode® 6.0.0: Released: 2010 October 11 (Announcement) | url = https://www.unicode.org/versions/Unicode6.0.0/

| edition = 6.0.0 | publisher = The Unicode Consortium | isbn = 978-1-936213-01-6 | location = Mountain View, California, US | access-date = 2025-08-23 | url-status = live | archive-url = https://web.archive.org/web/20250728233736/https://www.unicode.org/versions/Unicode6.0.0/ | archive-date = 2025-07-28 }}</ref> As of 2026, almost every webpage (99%) is transmitted as UTF-8.<ref name="W3TechsWebEncoding" />

UTF-8 supports all 1,112,064<ref>{{cite book | title = Unicode 16.0.0: Core Spec / Chapter 3 | chapter-url = https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-3/#G7404 | edition = 6.0.0 | at = 3.9 Unicode Encoding Forms | chapter = Conformance | quote = Each encoding form maps the Unicode code points U+0000..U+D7FF and U+E000..U+10FFFF | publisher = The Unicode Consortium | isbn = 978-1-936213-34-4 | location = Mountain View, California, US | url-status = live | archive-url = https://web.archive.org/web/20250701110809/https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-3/#G7404 | archive-date = 2025-07-01 | access-date = 2025-08-23 }}</ref> valid Unicode code points using a variable-width encoding of one to four one-byte (8-bit) code units.

Code points with lower numerical values, which tend to occur more frequently, are encoded using fewer bytes. It was designed for backward compatibility with ASCII: the first 128 characters of Unicode, which correspond one-to-one with ASCII, are encoded using a single byte with the same binary value as ASCII, so that a UTF-8-encoded file using only those characters is identical to an ASCII file. Most software designed for any extended ASCII can read and write UTF-8, and this results in fewer internationalization issues than any alternative text encoding.<ref name="Microsoft GDK" /><ref name=":3">{{Cite web |title=Encoding Standard |url=https://encoding.spec.whatwg.org/#preface |access-date=2025-11-20 |website=encoding.spec.whatwg.org}}</ref>

UTF-8 is dominant for all countries/languages on the internet, is used in most standards, often the only allowed encoding, and is supported by all modern operating systems and programming languages.

== History == {{See also|Universal Coded Character Set#History}} The International Organization for Standardization (ISO) set out to compose a universal multi-byte character set in 1989. The draft ISO 10646 standard contained a non-required annex called UTF-1 that provided a byte stream encoding of its 32-bit code points. This encoding was not satisfactory on performance grounds, among other problems, and the biggest problem was probably that it did not have a clear separation between ASCII and non-ASCII: new UTF-1 tools would be backward compatible with ASCII-encoded text, but UTF-1-encoded text could confuse existing code expecting ASCII (or extended ASCII), because it could contain continuation bytes in the range {{mono|0x21}}–{{mono|0x7E}} that meant something else in ASCII, e.g., {{mono|0x2F}} for <code>/</code>, the Unix path directory separator.

In July 1992, the X/Open committee XoJIG was looking for a better encoding. Dave Prosser of Unix System Laboratories submitted a proposal for one that had faster implementation characteristics and introduced the improvement that 7-bit ASCII characters would ''only'' represent themselves; multi-byte sequences would only include bytes with the high bit set. The name ''File System Safe UCS Transformation Format'' (''FSS-UTF'')<ref>{{cite web|url=https://www.unicode.org/L2/Historical/wg20-n193-fss-utf.pdf|title=File System Safe UCS — Transformation Format (FSS-UTF) - X/Open Preliminary Specification|website=unicode.org}}</ref> and most of the text of this proposal were later preserved in the final specification.<ref name="FSS-UTF">{{cite journal |title=Appendix F. FSS-UTF / File System Safe UCS Transformation format |journal=The Unicode Standard 1.1 |url=https://www.unicode.org/versions/Unicode1.1.0/appF.pdf |access-date=2016-06-07 |url-status=live |archive-url=https://web.archive.org/web/20160607215950/https://www.unicode.org/versions/Unicode1.1.0/appF.pdf |archive-date=2016-06-07}}</ref><ref>{{Cite mailing list |last=Whistler |first=Kenneth |date=2001-06-12 |mailing-list=Unicode Mail List |title=FSS-UTF, UTF-2, UTF-8, and UTF-16 |url=https://unicode.org/mail-arch/unicode-ml/y2001-m06/0318.html |url-status=live |archive-url=https://web.archive.org/web/20160607220249/https://unicode.org/mail-arch/unicode-ml/y2001-m06/0318.html |archive-date=2016-06-07 |access-date=2025-11-20}}</ref><ref name="pikeviacambridge">{{cite web |url=https://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt |title=UTF-8 history |author-first=Rob |author-last=Pike |author-link=Rob Pike |date=2003-04-30 |access-date=2012-09-07}}</ref> In August 1992, this proposal was circulated by an IBM X/Open representative to interested parties.

A modification by Ken Thompson of the Plan 9 operating system group at Bell Labs made it self-synchronizing, letting a reader start anywhere and immediately detect character boundaries, at the cost of being somewhat less bit-efficient than the previous proposal. It also abandoned the use of biases that prevented overlong encodings.<ref name=pikeviacambridge/><ref>At that time subtraction was slower than bit logic on many computers, and speed was considered necessary for acceptance.{{citation needed|date=October 2024}}</ref> Thompson's design was outlined on September 2, 1992, on a placemat in a New Jersey diner with Rob Pike. In the following days, Pike and Thompson implemented it and updated Plan 9 to use it throughout,<ref>{{cite book |chapter-url=https://www.cl.cam.ac.uk/~mgk25/ucs/UTF-8-Plan9-paper.pdf |chapter=Hello World or Καλημέρα κόσμε or こんにちは世界 |title=Proceedings of the Winter 1993 USENIX Conference |first1=Rob |last1=Pike |first2=Ken |last2=Thompson |year=1993}}</ref> and then communicated their success back to X/Open, which accepted it as the specification for FSS-UTF.<ref name=pikeviacambridge/> UTF-8 was first officially presented at the USENIX conference in San Diego, from January 25 to 29, 1993.<ref>{{Cite web |title=USENIX WINTER 1993 CONFERENCE PROCEEDINGS |url=https://www.usenix.org/legacy/publications/library/proceedings/sd93/ |access-date=2025-11-20 |website=www.usenix.org}}</ref> The Internet Engineering Task Force adopted UTF-8 in its Policy on Character Sets and Languages in RFC 2277 (<abbr title="Best Current Practice">BCP</abbr> 18) for future internet standards work in January 1998, replacing Single Byte Character Sets such as Latin-1 in older RFCs.<ref name="rfc2277">{{cite IETF |rfc=2277 |bcp=18 |title=IETF Policy on Character Sets and Languages |date=January 1998 |last1=Alvestrand |first1=Harald T. |author-link=Harald Alvestrand |publisher=IETF}}</ref>

In November 2003, UTF-8 was restricted by {{IETF RFC|3629}} to match the constraints of the UTF-16 character encoding: explicitly prohibiting code points corresponding to the high and low surrogate characters removed  more than 3% of the three-byte sequences, and ending at {{tt|U+10FFFF}} removed  more than 48% of the four-byte sequences and all five- and six-byte sequences.<ref>{{cite web |author-last=Pike |author-first=Rob |author-link=Rob Pike |date=2012-09-06 |title=UTF-8 turned 20 years old yesterday |url=https://plus.google.com/u/0/101960720994009339267/posts/Rz1udTvtiMg |url-status=dead |archive-url=https://web.archive.org/web/20121130120145/https://plus.google.com/u/0/101960720994009339267/posts/Rz1udTvtiMg |archive-date=2012-11-30 |access-date=2012-09-07 }}</ref>

== Description == UTF-8 encodes code points in one to four bytes, depending on the value of the code point. In the following table, the characters {{mono|'''u'''}} to {{mono|'''z'''}}, each representing a hexadecimal digit, are replaced by their constituent 4 bits {{mono|''uuuu''}} to {{mono|''zzzz''}}, from the positions {{mono|U+'''uvwxyz'''}}:

{| class="wikitable" |+ Code point ↔ UTF-8 conversion |- ! First code point ! Last code point ! Byte 1 ! Byte 2 ! Byte 3 ! Byte 4 |- | style="text-align: right" | {{tt|U+0000}} | style="text-align: right" | {{tt|U+007F}} | {{mono|0''yyyzzzz''}} | style="background: darkgray" colspan=3 | |- | style="text-align: right" | {{tt|U+0080}} | style="text-align: right" | {{tt|U+07FF}} | {{mono|110''xxxyy''}} | {{mono|10''yyzzzz''}} | style="background: darkgray" colspan=2 | |- | style="text-align: right" | {{tt|U+0800}} | style="text-align: right" | {{tt|U+FFFF}} | {{mono|1110''wwww''}} | {{mono|10''xxxxyy''}} | {{mono|10''yyzzzz''}} | style="background: darkgray" | |- | style="text-align: right" | {{tt|U+010000}} | style="text-align: right" | {{tt|U+10FFFF}} | {{mono|11110''uvv''}} | {{mono|10''vvwwww''}} | {{mono|10''xxxxyy''}} | {{mono|10''yyzzzz''}} |}

As an example, the character 桁 has the hexadecimal code point {{mono|U+6841}}, which is {{mono|0110 1000 0100 0001}} in binary, which makes its UTF-8 encoding {{mono|11100110 10100001 10000001}}.

The first 128 code points (ASCII) need 1 byte. The next 1,920 code points need two bytes to encode, which covers the remainder of almost all Latin-script alphabets, and also IPA extensions, Greek, Cyrillic, Coptic, Armenian, Hebrew, Arabic, Syriac, Thaana and N'Ko alphabets, as well as Combining Diacritical Marks. Three bytes are needed for the remaining 61,440 codepoints of the Basic Multilingual Plane (BMP), including most Chinese, Japanese and Korean characters. Four bytes are needed for the 1,048,576 non-BMP code points, which include emoji, less common CJK characters, and other useful characters.<ref>{{Cite web |last=Lunde |first=Dr Ken |date=2022-01-09 |title=2022 Top Ten List: Why Support Beyond-BMP Code Points? |url=https://ken-lunde.medium.com/2022-top-ten-list-why-support-beyond-bmp-code-points-6a946d7735f9 |access-date=2025-11-20 |website=Medium |language=en}}</ref>

UTF-8 is a ''prefix code'' and it is unnecessary to read past the last byte of a code point to decode it. Unlike many earlier multi-byte text encodings such as Shift-JIS, it is ''self-synchronizing'' so searches for short strings or characters are possible; and the start of a code point can be found from a random position by backing up at most 3 bytes. The values chosen for the lead bytes means sorting a list of UTF-8 strings puts them in the same order as sorting UTF-32 strings.

=== Overlong encodings === {{anchor|overlong encodings}} Using a row in the above table to encode a code point less than "First code point" (thus using more bytes than necessary) is termed an ''overlong encoding''. These are a security problem because they allow character sequences to bypass other security validations like the blocking of <code>../</code> or of malicious JavaScript. There have been numerous high-profile vulnerabilities involving overlong encodings reported in products such as Microsoft's IIS web server<ref name=MS00-078>{{ cite report | first = Marvin |last = Marin | date = 2000-10-17 | title = Windows NT UNICODE vulnerability analysis | department = Web server folder traversal | id = MS00-078 | series = Malware FAQ | website=SANS Institute | url=https://www.sans.org/resources/malwarefaq/wnt-unicode.php | url-status=dead | archive-url=https://web.archive.org/web/20140827001204/http://www.sans.org/security-resources/malwarefaq/wnt-unicode.php | archive-date=Aug 27, 2014 }}</ref> and Apache's Tomcat servlet container.<ref name="CVE-2008-2938">{{cite web |year=2008 |title=CVE-2008-2938 |url=https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2008-2938 |access-date=2025-11-20 |website=National Vulnerability Database (nvd.nist.gov) |publisher=U.S. National Institute of Standards and Technology}}</ref> Overlong encodings should therefore be considered an error and never decoded.

=== Error handling === Not all sequences of bytes are valid UTF-8. A UTF-8 decoder should be prepared for:

* A "continuation byte" ({{tt|0x80}}{{ndash}}{{tt|0xBF}}) at the start of a character * A non-continuation byte (or the string ending) before the end of a character * An overlong encoding ({{tt|0xC0}}, {{tt|0xC1}}, {{tt|0xE0}} followed by less than {{tt|0xA0}}, or {{tt|0xF0}} followed by less than {{tt|0x90}}) * A multi-byte sequence that decodes to a value greater than {{tt|U+10FFFF}} ({{tt|0xF4}} followed by {{tt|0x90}} or greater, {{tt|0xF5}}{{ndash}}{{tt|0xFF}})

Many of the first UTF-8 decoders would decode these, ignoring incorrect bits. Carefully crafted invalid UTF-8 could make them either skip or create ASCII characters such as {{mono|NUL}}, slash, or quotes, leading to security vulnerabilities. {{nobr|RFC 3629}} states "Implementations of the decoding algorithm MUST protect against decoding invalid sequences."<ref name="rfc3629">{{cite IETF |title=UTF-8, a transformation format of ISO 10646 |rfc=3629 |std=63 |last1=Yergeau |first1=F. |date=November 2003 |publisher=IETF |access-date=August 20, 2020}}</ref> ''The Unicode Standard'' requires decoders to: "... treat any ill-formed code unit sequence as an error condition. This guarantees that it will neither interpret nor emit an ill-formed code unit sequence."

It was common to throw an exception or truncate the string at an error<ref>{{Cite web |title=DataInput (Java Platform SE 8 ) |url=https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html |access-date=2025-11-20 |website=docs.oracle.com}}</ref> but this turns what would otherwise be harmless errors (i.e. "file not found") into a denial of service, for instance early versions of Python 3.0 would exit immediately if the command line or environment variables contained invalid UTF-8.<ref name="pep383"/> Most code now replaces each error with a single code point (such as {{unichar|FFFD|nlink=replacement character}}) and continue decoding.{{Citation needed|reason=There are different versions of the standard and it is unclear to which version "now" refers to. A check of Unicode17.0.0 Core does not find a match of this recommendation easily|date=April 2026}}

Some decoders consider the sequence {{mono|E1,A0,20}} (a truncated 3-byte code followed by a space) as a single error. This is not a good idea as a search for a space character would find the one hidden in the error. Since Unicode 6 (October 2010)<ref name=":1" /> the standard (chapter 3) has recommended a "best practice" where the error is either one continuation byte, or ends at the first byte that is disallowed, so {{mono|E1,A0,20}} is a two-byte error followed by a space. An error is no more than three bytes long, never contains the start of a valid character, and there are {{val|21952|fmt=commas}} different possible errors. Many decoders instead make ''each'' byte be an error, in which case {{mono|E1,A0,20}} is ''two'' errors followed by a space; there are now only 128 different errors which makes it practical to store the errors in the output string,<ref name="pep383"/> or replace them with characters from a legacy encoding.

Only a small subset of possible byte strings are error-free UTF-8: several bytes cannot appear, a byte with the high bit set cannot be alone, and in a truly random string a byte with a high bit set has only a {{frac|1|15}} chance of starting a valid UTF-8 character. This has the consequence of making it easy to detect if a legacy text encoding is accidentally used instead of UTF-8, making conversion of a system to UTF-8 easier and avoiding the need to require a Byte Order Mark or any other metadata.

=== Surrogates === {{anchor|WTF-8}} Since RFC 3629 (November 2003), the high and low surrogates used by UTF-16 ({{tt|U+D800}} through {{tt|U+DFFF}}) are not legal Unicode values, and their UTF-8 encodings must be treated as an invalid byte sequence.<ref name="rfc3629"/> These encodings all start with {{tt|0xED}} followed by {{tt|0xA0}} or higher. This rule is often ignored as surrogates are allowed in Windows filenames and this means there must be a way to store them in a string.<ref>{{Cite web |title=PEP 529 – Change Windows filesystem encoding to UTF-8 {{!}} peps.python.org |url=https://peps.python.org/pep-0529/ |access-date=2025-11-20 |website=Python Enhancement Proposals (PEPs) |language=en}}</ref> UTF-8 that allows these surrogate halves has been (informally) called ''WTF-8'', for "wobbly transformation format",<ref>{{Cite web |title=The WTF-8 encoding |url=https://wtf-8.codeberg.page |access-date=2025-11-30 |website=wtf-8.codeberg.page}}</ref> while another variation that also encodes all non-BMP characters as two surrogates (6 bytes instead of 4) is called ''CESU-8''.

=== Byte map === The chart below gives the detailed meaning of each byte in a stream encoded in UTF-8. {{UTF-8 byte map}}

=== Byte-order mark === If the Unicode byte-order mark {{tt|U+FEFF}} is at the start of a UTF-8 file, the first three bytes will be {{mono|0xEF}}, {{mono|0xBB}}, {{mono|0xBF}}.

The Unicode Standard neither requires nor recommends the use of the BOM for UTF-8, but warns that it may be encountered at the start of a file trans-coded from another encoding.<ref>{{citation | chapter-url = https://www.unicode.org/versions/Unicode15.0.0/ch02.pdf | title = The Unicode Standard — Version 15.0.0 | chapter = Chapter 2 | page = 39 }}</ref> While ASCII text encoded using UTF-8 is backward compatible with ASCII, this is not true when Unicode Standard recommendations are ignored and a BOM is added. A BOM can confuse software that isn't prepared for it but can otherwise accept UTF-8, e.g. programming languages that permit non-ASCII bytes in string literals but not at the start of the file. Nevertheless, there was and still is software that always inserts a BOM when writing UTF-8, and refuses to correctly interpret UTF-8 unless the first character is a BOM (or the file only contains ASCII).{{citation needed|date=March 2026}}

=== Older standards ===

Earlier standards for UTF-8, like {{IETF RFC|2279}}, could encode up to 31 bits in 6 bytes, as shown in the table below. The current {{IETF RFC|3629}} allows only up to 4 bytes.thumb|An older UTF-8 encoding scheme, defined before Unicode 4.0, that could encode up to 31 bits. For this table the characters {{mono|'''s'''}} to {{mono|'''z'''}}, each representing a hexadecimal digit, are replaced by their constituent 4 bits {{mono|''ssss''}} to {{mono|''zzzz''}}, from the positions {{mono|U+'''stuvwxyz'''}}:

{| class="wikitable" |+ Code point ↔ UTF-8 conversion as defined in {{IETF RFC|2279}} |- ! First code point ! Last code point ! Byte 1 ! Byte 2 ! Byte 3 ! Byte 4 ! Byte 5 ! Byte 6 |- | style="text-align: right" | {{tt|U+0000}} | style="text-align: right" | {{tt|U+007F}} | {{mono|0''yyyzzzz''}} | style="background: darkgray" colspan=5 | |- | style="text-align: right" | {{tt|U+0080}} | style="text-align: right" | {{tt|U+07FF}} | {{mono|110''xxxyy''}} | {{mono|10''yyzzzz''}} | style="background: darkgray" colspan=4 | |- | style="text-align: right" | {{tt|U+0800}} | style="text-align: right" | {{tt|U+FFFF}} | {{mono|1110''wwww''}} | {{mono|10''xxxxyy''}} | {{mono|10''yyzzzz''}} | style="background: darkgray" colspan=3 | |- | style="text-align: right" | {{tt|U+010000}} | style="text-align: right" | {{tt|U+1FFFFF}} | {{mono|11110''uvv''}} | {{mono|10''vvwwww''}} | {{mono|10''xxxxyy''}} | {{mono|10''yyzzzz''}} | style="background: darkgray" colspan=2 | |- | style="text-align: right;" |{{tt|U+200000}} | style="text-align: right;" |{{tt|U+3FFFFFF}} | {{mono|111110''tt''}} | {{mono|10''uuuuvv''}} | {{mono|10''vvwwww''}} | {{mono|10''xxxxyy''}} | {{mono|10''yyzzzz''}} | style="background: darkgray;" | |- | style="text-align: right;" |{{tt|U+4000000}} | style="text-align: right;" |{{tt|U+7FFFFFFF}} | {{mono|1111110''s''}} | {{mono|10''sstttt''}} | {{mono|10''uuuuvv''}} | {{mono|10''vvwwww''}} | {{mono|10''xxxxyy''}} | {{mono|10''yyzzzz''}} |}

== Comparison to UTF-16 == {{See also|Comparison of Unicode encodings}}

For a long time there was considerable argument as to whether it was better to process text in UTF-16 or in UTF-8.{{citation needed|date=March 2026}} The primary advantage of UTF-16 is that the Windows API required it for access to all Unicode characters (UTF-8 was not fully supported in Windows until May 2019). This caused several libraries such as Qt to also use UTF-16 strings which propagates this requirement to non-Windows platforms.

In the early days of Unicode, there were no characters greater than {{tt|U+FFFF}} and combining characters were rarely used, so the 16-bit encoding was effectively fixed-size. Some believed fixed-size encoding could make processing more efficient, but any such advantages were lost as soon as UTF-16 became variable width as well.

The code points {{tt|U+0800}}–{{tt|U+FFFF}} take 3 bytes in UTF-8 but only 2 in UTF-16. This led to the idea that text in Chinese and other languages would take more space in UTF-8. However, text is only larger if there are more of these code points than 1-byte ASCII code points, and this rarely happens in real-world documents due to markup,<ref>{{cite web |last1=Radzivilovsky |first1=Pavel |last2=Galka |first2=Yakov |last3=Novgorodov |first3=Slava |title=UTF-8 Everywhere Manifesto |url=https://utf8everywhere.org/#asian |website=UTF-8 Everywhere |access-date=25 March 2026 |ref=manifesto-asian}}</ref> along with spaces, newlines, digits, punctuation, English words, etc..

UTF-8 has the advantages of being trivial to retrofit to any system that could handle an extended ASCII, not having byte-order problems, and taking about half the space for any language using mostly Latin letters.

== Implementations and adoption == thumb|Declared character set for the 10 million most popular websites from 2010 to 2021 thumb|Use of the main encodings on the web from 2001 to 2012 as recorded by Google,<ref name=MarkDavis2012>{{ cite web | author-last=Davis |author-first=Mark |author-link=Mark Davis (Unicode) | date=2012-02-03 | title=Unicode over 60 percent of the web | website=Official Google blog | url=https://googleblog.blogspot.com/2012/02/unicode-over-60-percent-of-web.html | url-status=live |access-date=2020-07-24 | archive-url=https://web.archive.org/web/20180809152828/https://googleblog.blogspot.com/2012/02/unicode-over-60-percent-of-web.html | archive-date=2018-08-09 }}</ref> with UTF-8 overtaking all others in 2008 and over 60% of the web in 2012. UTF-8 is the only encoding of Unicode (explicitly) listed there, and the rest only provide subsets of Unicode. The ASCII-only figure includes all web pages that only contain ASCII characters, regardless of the declared header.

UTF-8 has been the most common encoding for the World Wide Web since 2008.<ref name="MarkDavis">{{Cite web |author-first=Mark |author-last=Davis |author-link=Mark Davis (Unicode) |date=2008-05-05|title=Moving to Unicode 5.1 |url=https://googleblog.blogspot.com/2008/05/moving-to-unicode-51.html |access-date=2023-03-13 |website=Official Google Blog |language=en}}</ref> {{As of|2026|01}}, UTF-8 is used by 98.9% of surveyed web sites.<ref name=W3TechsWebEncoding>{{Cite web|url=https://w3techs.com/technologies/cross/character_encoding/ranking |title=Usage Survey of Character Encodings broken down by Ranking |website=W3Techs |language=en |date=January 2026 |access-date=2026-01-03}}</ref> Although many pages only use ASCII characters to display content, very few websites now declare their encoding to only be ASCII instead of UTF-8.<ref>{{cite web |url=https://w3techs.com/technologies/details/en-usascii |title = Usage statistics and market share of ASCII for websites | date = December 2025 | website = W3Techs | access-date = 2025-12-17 }}</ref> Virtually all countries and  languages have 95% or more use of UTF-8 encodings on the web.

Many standards only support UTF-8, e.g. JSON exchange requires it (without a byte-order mark (BOM)).<ref name=rfc8259>{{ cite IETF | last = Bray | first = Tim | editor-last = Bray | editor-first = Tim | date = December 2017 | title = The JavaScript Object Notation (JSON) Data Interchange Format | publisher = IETF | doi = 10.17487/RFC8259 | access-date = 16 February 2018 | rfc = 8259 }}</ref> UTF-8 is also required by the WHATWG for HTML and DOM specifications, which states "UTF-8 encoding is the most appropriate encoding for interchange of Unicode",<ref name=":3" /> and the Internet Mail Consortium recommends that all e‑mail programs be able to display and create mail using UTF-8.<ref name=IMC>{{ cite web | url = https://www.imc.org/mail-i18n.html | title = Using International Characters in Internet Mail | publisher = Internet Mail Consortium | date = 1998-08-01 | access-date = 2007-11-08 | url-status = dead | archive-url = https://web.archive.org/web/20071026103104/https://www.imc.org/mail-i18n.html | archive-date = 2007-10-26}}</ref><ref>{{Cite web |title=Encoding Standard |url=https://encoding.spec.whatwg.org/#security-background |access-date=2025-11-20 |website=encoding.spec.whatwg.org}}</ref> The World Wide Web Consortium recommends UTF-8 as the default encoding in XML and HTML (and not just using UTF-8, also declaring it in metadata), "even when all characters are in the ASCII range ... Using non-UTF-8 encodings can have unexpected results". Version 5.3 of the W3C HTML specification and the current Living Standard by WHATWG both require UTF-8.<ref name=html5charset>{{cite report | section = Specifying the document's character encoding | title = HTML 5.3 | date = 28 January 2021 | publisher = World Wide Web Consortium | url = https://www.w3.org/TR/2021/NOTE-html53-20210128/document-metadata.html | section-url = https://www.w3.org/TR/2021/NOTE-html53-20210128/document-metadata.html#specifying-the-documents-character-encoding | access-date = 2026-01-06 | mode = cs1 }}</ref><ref name="html5whatwg">{{cite book |chapter-url=https://html.spec.whatwg.org/multipage/semantics.html#charset |chapter=Specifying the document's character encoding |title=HTML Standard |publisher=WHATWG |date=17 December 2025 |access-date=2026-01-06}}</ref>

Many software programs have the ability to read/write UTF-8. It may require the user to change options from the normal settings, or may require a BOM (byte-order mark) as the first character to read the file. Examples of software supporting UTF-8 include Microsoft Word,<ref>{{ cite web | title=Choose text encoding when you open and save files | website=Microsoft Support | url=https://support.microsoft.com/en-us/office/choose-text-encoding-when-you-open-and-save-files-60d59c21-88b5-4006-831c-d536d42fd861 | access-date=2021-11-01 }}</ref><ref>{{ cite web | title = Exporting a UTF-8 <code>.txt</code> file from ''Word'' | website = support.3playmedia.com | date = 14 March 2023 | url = https://support.3playmedia.com/hc/en-us/articles/227730088-Exporting-a-UTF-8-txt-file-from-Word }}</ref> Microsoft Excel (Office 2003 and later),<ref>{{ cite web | author1 = Abhinav, Ankit | author2 = Xu, Jazlyn | date = April 13, 2020 | title = How to open UTF-8 <code>CSV</code> file in ''Excel'' without mis-conversion of characters in Japanese and Chinese language for both Mac and Windows? | website = Microsoft Support Community | language = en-US | url = https://answers.microsoft.com/en-us/msoffice/forum/all/how-to-open-utf-8-csv-file-in-excel-without-mis/1eb15700-d235-441e-8b99-db10fafff3c2 | access-date = 2021-11-01 }}</ref> Google Drive, LibreOffice,<ref>{{ cite web | title = Save a CSV file as UTF-8 | series = LibreOffice | website = RO CSVI | url = https://rolandd.com/documentation/ro-csvi/save-a-csv-file-as-utf-8 | access-date = 2025-05-20 }}</ref> and most databases.

Software that "defaults" to UTF-8 (meaning it writes it without the user changing settings, and it reads it without a BOM) has become more common since 2010.<ref>{{cite web | last=Galloway |first=Matt | date=October 2012 | title=Character encoding for iOS developers; or, UTF-8 what now? | website=www.galloway.me.uk | language=en-UK | url=https://www.galloway.me.uk/2012/10/character-encoding-for-ios-developers-utf8/ | access-date=2021-01-02 | quote = ... in reality, you usually just assume UTF-8 since that is by far the most common encoding. }}</ref>{{unreliable source|certain=y|reason=Personal blog|date=January 2026}} Windows Notepad, in all currently supported versions of Windows, defaults to writing UTF-8 without a BOM (a change from {{nobr|Windows 7}} ''Notepad''), bringing it into line with most other text editors.<ref>{{ cite web | title=Windows 10 Notepad is getting better UTF-8 encoding support | website=BleepingComputer | url=https://www.bleepingcomputer.com/news/microsoft/windows-10-notepad-is-getting-better-utf-8-encoding-support/ | access-date=2021-03-24 | quote=Microsoft is now defaulting to saving new text files as UTF-8 without BOM, as shown below. | language=en-us }}</ref> Some system files on Windows 11 require UTF-8<ref>{{ cite web | title = Customize the Windows 11 ''Start'' menu | url=https://docs.microsoft.com/en-us/windows-hardware/customize/desktop/customize-the-windows-11-start-menu | access-date=2021-06-29 | website=docs.microsoft.com | language=en-us | quote=Make sure your LayoutModification.json uses UTF-8 encoding. }}</ref> with no requirement for a BOM, and almost all files on macOS and most Linux distributions are required to be UTF-8 without a BOM.{{citation needed|date=June 2021}} Programming languages that default to UTF-8 for I/O include Ruby 3.0,<ref>{{ cite web | title = Set default for Encoding.default_external to UTF-8 on Windows | series = Ruby master | id = Feature #16604 | website = Ruby Issue Tracking System (bugs.ruby-lang.org) | url = https://bugs.ruby-lang.org/issues/16604 | access-date = 2022-08-01 }}</ref><ref>{{ cite web | title = Feature #12650: Use UTF-8 encoding for ENV on Windows | series = Ruby master | website = Ruby Issue Tracking System | url = https://bugs.ruby-lang.org/issues/12650 | access-date = 2022-08-01 }}</ref> R 4.2.2,<ref>{{ cite web | title = New features in R 4.2.0 | date = 2022-04-01 | website = R bloggers | series = The Jumping Rivers Blog | url = https://www.r-bloggers.com/2022/04/new-features-in-r-4-2-0/ | access-date = 2022-08-01 | language = en-US }}</ref> Raku and Java 18.<ref name=Java_UTF-8_and_UTF-16>{{ cite web | title = UTF-8 by default | id = JEP 400 | website = openjdk.java.net | url = https://openjdk.java.net/jeps/400 | access-date=2022-03-30 }}</ref> Python 3.15 makes UTF-8 the default for I/O;<ref>{{Cite web |title=What's new in Python 3.15 |url=https://docs.python.org/3.15/whatsnew/3.15.html |access-date=2025-12-23 |website=Python documentation |language=en}}</ref><ref>{{ cite web | title = Make UTF-8 mode default | website = peps.python.org | id = PEP 686 | url = https://peps.python.org/pep-0686/ | access-date=2023-07-26 }}</ref> previous versions require an option to <code>open()</code> to read/write UTF-8.<ref>{{cite web | title = add a new UTF-8 mode | website = peps.python.org | id = PEP 540 | url = https://peps.python.org/pep-0540/ | access-date = 2022-09-23 }}</ref> C++23 adopted UTF-8 as the only portable source code file format.<ref>{{ cite report | title = Support for UTF-8 as a portable source file encoding | year = 2022 | id = p2295r6 | website = open-std.org | url = https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2295r6.pdf }}</ref>

Backwards compatibility is a serious impediment to changing code and APIs using UTF-16 to use UTF-8, but this is happening. In May 2019, Microsoft added the capability for an application to set UTF-8 as the "code page" for the Windows API, removing the need to use UTF-16; and more recently has recommended programmers use UTF-8,<ref name="Microsoft-UTF-8">{{cite web | title=Use UTF-8 code pages in Windows apps | website=Microsoft Learn | date=20 August 2024 |language=en-us | url=https://learn.microsoft.com/en-us/windows/apps/design/globalizing/use-utf8-code-page | access-date=2024-09-24}}</ref> and even states "UTF-16 [...] is a unique burden that Windows places on code that targets multiple platforms".<ref name="Microsoft GDK">{{cite web | title=UTF-8 support in the Microsoft GDK | series = Microsoft Game Development Kit (GDK) | website = Microsoft Learn |language=en-us | url=https://learn.microsoft.com/en-us/gaming/gdk/_content/gc/system/overviews/utf-8 | access-date = 2023-03-05 }}</ref> The default string primitive in Go,<ref>{{cite report | section=Source code representation | title=The ''Go'' Programming Language Specification | website=golang.org | section-url=https://golang.org/ref/spec#Source_code_representation | access-date=2021-02-10 }}</ref> Julia, Rust, Swift (since version 5),<ref>{{cite web | last=Tsai |first=Michael J. | date=21 March 2019 | title=UTF-8 string in Swift 5 | type=blog post |language=en | url=https://mjtsai.com/blog/2019/03/21/utf-8-string-in-swift-5/ | access-date=2021-03-15 }}</ref> and PyPy<ref>{{Cite web |last=Mattip |date=2019-03-24 |title=PyPy v7.1 released; now uses utf-8 internally for unicode strings |url=https://morepypy.blogspot.com/2019/03/pypy-v71-released-now-uses-utf-8.html |access-date=2025-11-20 |website=PyPy Status Blog}}</ref> uses UTF-8 internally in all cases. Python (since version 3.3) uses UTF-8 internally for Python C API extensions<ref name=PEP393>{{cite web | title = Flexible String Representation | id = PEP 393 | website = Python.org |language=en | url = https://peps.python.org/pep-0393 | access-date = 2022-05-18 }}</ref><ref>{{Cite web |title=Common Object Structures |url=https://docs.python.org/3/c-api/structures.html |access-date=2025-11-20 |website=Python documentation |language=en}}</ref> and sometimes for strings<ref name=PEP393/><ref>{{cite web | title=Unicode objects and codecs | url=https://docs.python.org/3/c-api/unicode.html | access-date=2023-08-19 |website=Python documentation | quote=UTF-8 representation is created on demand and cached in the Unicode object.}}</ref> and a future version of Python is planned to store strings as UTF-8 by default.<ref>{{cite web | title=PEP 623 – remove wstr from Unicode | website=Python.org |language=en | url=https://www.python.org/dev/peps/pep-0623/ | access-date=2020-11-21 }}</ref><ref>{{ cite web | last=Wouters |first=Thomas | date=2023-07-11 | title=Python 3.12.0 beta 4 released | website = Python Insider | type = blog post | url=https://pythoninsider.blogspot.com/2023/07/pleased-to-announce-release-of-python-3.html | access-date=2023-07-26 | quote=The deprecated <code>wstr</code> and <code>wstr_length</code> members of the C implementation of unicode objects were removed, per PEP 623. }}</ref> Modern versions of Microsoft Visual Studio use UTF-8 internally.<ref>{{cite web | title=validate-charset (validate for compatible characters) | website=docs.microsoft.com |language=en-us | url=https://docs.microsoft.com/en-us/cpp/build/reference/validate-charset-validate-for-compatible-characters | access-date=2021-07-19 | quote=Visual Studio uses UTF-8 as the internal character encoding during conversion between the source character set and the execution character set. }}</ref> All currently supported versions of Microsoft SQL Server  support UTF-8 for importing and exporting, and in addition all on mainstream support, i.e. since SQL Server 2019, support UTF-8 internally, and using it results in a 35% speed increase, and "nearly 50% reduction in storage requirements".<ref>{{cite web | title = Introducing UTF-8 support for SQL Server | date = 2019-07-02 | website = techcommunity.microsoft.com | url = https://techcommunity.microsoft.com/t5/sql-server/introducing-utf-8-support-for-sql-server/ba-p/734928 | access-date = 2021-08-24 | language = en-US }}</ref>

{{anchor|Modified UTF-8}}Java internally uses UTF-16 for the <code>char</code> data type and, consequentially, the <code>Character</code>, <code>String</code>, and <code>StringBuffer</code> classes,<ref>{{cite web |title=Character (Java SE 24 & JDK 24) |url=https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/lang/Character.html#unicode |year=2025 |publisher=Oracle Corporation |access-date=2025-04-08}}</ref> but for I/O uses ''"Modified UTF-8"'', which is the same as CESU-8, except the null character {{tt|U+0000}} uses the two-byte overlong encoding {{tt|0xC0}} {{tt|0x80}} instead of just {{tt|0x00}}.<ref name=":2">{{cite web |title=Java SE documentation for Interface java.io.DataInput, subsection on Modified UTF-8 |url=https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8 |year=2015 |publisher=Oracle Corporation |access-date=2015-10-16}}</ref> Modified UTF-8 strings never contain any actual null bytes but can contain all Unicode code points including {{tt|U+0000}},<ref name=":0">{{cite web |url=https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.7 |title=The Java Virtual Machine Specification, section 4.4.7: The CONSTANT_Utf8_info Structure |publisher=Oracle Corporation |year=2015 |access-date=2015-10-16}}</ref> which allows such strings (with a null byte appended) to be processed by traditional null-terminated string functions. Java reads and writes normal UTF-8 to files and streams,<ref>{{Javadoc:SE|java/io|InputStreamReader}} and {{Javadoc:SE|java/io|OutputStreamWriter}}</ref> but it uses Modified UTF-8 for object serialization,<ref>{{cite web |title=Java Object Serialization Specification, chapter 6: Object Serialization Stream Protocol, section 2: Stream Elements |url=https://docs.oracle.com/javase/8/docs/platform/serialization/spec/protocol.html#a8299 |year=2010 |publisher=Oracle Corporation |access-date=2015-10-16}}</ref><ref>{{Javadoc:SE|java/io|DataInput}} and {{Javadoc:SE|java/io|DataOutput}}</ref> for the Java Native Interface,<ref>{{cite web |url=https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/types.html#modified_utf_8_strings |title=Java Native Interface Specification, chapter 3: JNI Types and Data Structures, section: Modified UTF-8 Strings |publisher=Oracle Corporation |year=2015 |access-date=2015-10-16}}</ref> and for embedding constant strings in Java class files.<ref name=":0" /> The dex format defined by Dalvik also uses the same modified UTF-8 to represent string values.<ref>{{cite web |url=https://source.android.com/tech/dalvik/dex-format.html |title=ART and Dalvik |work=Android Open Source Project |access-date=2013-04-09 |url-status=dead |archive-url=https://web.archive.org/web/20130426010617/https://source.android.com/tech/dalvik/dex-format.html |archive-date=2013-04-26 }}</ref> Tcl also uses the same modified UTF-8<ref>{{cite web |title=UTF-8 bit by bit |date=2001-02-28 |url=https://wiki.tcl-lang.org/page/UTF-8+bit+by+bit |access-date=2022-09-03 |website=Tcler's Wiki}}</ref> as Java for internal representation of Unicode data, but uses strict CESU-8 for external data.

The Raku programming language (formerly Perl 6) uses <code>utf-8</code> encoding by default for I/O (Perl 5 also supports it); though that choice in Raku also implies "normalization into Unicode NFC (normalization form canonical). In some cases the user will want to ensure no normalization is done; for this "<code>utf8-c8</code>" can be used.<ref>{{Cite web |title=encoding |website=Raku Documentation |url=https://docs.raku.org/routine/encoding |access-date=2025-11-20}}</ref> That ''UTF-8 Clean-8'' variant, implemented by Raku, is an encoder/decoder  that preserves bytes as is (even illegal UTF-8 sequences) and allows for Normal Form Grapheme synthetics.<ref>{{Cite web |title=Unicode |website=Raku Documentation |url=https://docs.raku.org/language/unicode#UTF8-C8 |access-date=2025-11-20}}</ref>

Version 3 of the Python programming language treats each byte of an invalid UTF-8 bytestream as an error (see also changes with new UTF-8 mode in Python 3.7<ref>{{Cite web |title=PEP 540 – Add a new UTF-8 Mode |url=https://peps.python.org/pep-0540/ |access-date=2025-11-20 |website=Python Enhancement Proposals (PEPs) |language=en}}</ref>); this gives 128 different possible errors. Extensions have been created to allow any byte sequence that is assumed to be UTF-8 to be losslessly transformed to UTF-16 or UTF-32, by translating the 128 possible error bytes to 128 reserved code points, and transforming those code points back to error bytes to output UTF-8. The most common approach is to translate the codes to {{tt|U+DC80}}...{{tt|U+DCFF}} which are low (trailing) surrogate values and thus "invalid" UTF-16, as used by Python's PEP 383 (or "surrogateescape") approach.<ref name="pep383">{{cite web |last=von Löwis |first=Martin |date=2009-04-22 |title=Non-decodable Bytes in System Character Interfaces |url=https://www.python.org/dev/peps/pep-0383 |access-date=2025-11-20 |publisher=Python Software Foundation |language=en |id=PEP 383}}</ref> NumPy version 2.0, and its file formats, support UTF-8 (adding StringDType for it).<ref>{{Cite web |title=NEP 55 – Add a UTF-8 variable-width string DType to NumPy |website=NumPy Enhancement Proposals |url=https://numpy.org/neps/nep-0055-string_dtype.html |access-date=2025-11-20}}</ref> Another encoding called MirBSD OPTU-8/16 converts them to {{tt|U+EF80}}...{{tt|U+EFFF}} in a Private Use Area.<ref>{{cite web |title=RTFM optu8to16(3), optu8to16vis(3) |url=https://www.mirbsd.org/htman/i386/man3/optu8to16.htm |access-date=2025-11-20 |website=MirBSD}}</ref> In either approach, the byte value is encoded in the low eight bits of the output code point. These encodings are needed if invalid UTF-8 is to survive translation to and then back from the UTF-16 used internally by Python, and as Unix filenames can contain invalid UTF-8 it is necessary for this to work.<ref name="davis383">{{cite web |last1=Davis |first1=Mark |author-link1=Mark Davis (Unicode) |last2=Suignard |first2=Michel |year=2014 |title=3.7 Enabling Lossless Conversion |url=https://www.unicode.org/reports/tr36/#EnablingLosslessConversion |access-date=2025-11-20 |work=Unicode Security Considerations |id=Unicode Technical Report #36}}</ref>

Most file systems on Unix-like systems can use UTF-8 to encode file names, as looking up file names is done by comparing the bytes of file names. Linux's ext4 and macOS's APFS file systems support case-insensitive file name lookups, which require that the encoding of file names be specified; ext4 supports UTF-8 and uses it by default,<ref>{{cite web |title=Ext4 General Information |website=Linux Kernel documentation |url=https://www.kernel.org/doc/html/latest/admin-guide/ext4.html |access-date=2025-11-20}}</ref> and APFS requires UTF-8.<ref>{{cite web |title=Frequently Asked Questions |url=https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/APFS_Guide/FAQ/FAQ.html |access-date=2025-11-20 |work=Apple File System Guide |publisher=Apple}}</ref> Apple's older HFS Plus uses UTF-16 for file names, but uses UTF-8 in symbolic links.<ref>{{cite web |title=Technical Note TN1150: HFS Plus Volume Format |url=https://developer.apple.com/library/archive/technotes/tn/tn1150.html |access-date=2025-11-20 |publisher=Apple}}</ref> Windows' filesystem, NTFS, uses UTF-16 for file names.

== Standards == The official name for the encoding is {{code|UTF-8}}, the spelling used in all Unicode Consortium documents. The hyphen-minus is required and no spaces are allowed. Some other names used are:

* Many standards are case-insensitive and {{code|utf-8}} is often used.{{citation needed|date=March 2023}} * Web standards (which include CSS, HTML, XML, and HTTP headers) also allow {{code|utf8}} and many other aliases.<ref>{{cite web|url=https://encoding.spec.whatwg.org/#names-and-labels|title=Encoding Standard § 4.2. Names and labels|publisher=WHATWG|access-date=2018-04-29}}</ref> HTML documents, however, must have their encoding specified as "an ASCII case-insensitive match for the string 'utf-8{{'"}}.<ref name="html5charset"/> * The official Internet Assigned Numbers Authority lists {{code|csUTF8}} as the only alias,<ref name="IANA_2013_CS">{{cite web |publisher=Internet Assigned Numbers Authority |url=https://www.iana.org/assignments/character-sets |title=Character Sets |date=2013-01-23 |access-date=2013-02-08}}</ref> which is rarely used. * In some locales {{code|UTF-8N}} means UTF-8 ''without'' a byte-order mark (BOM), and in this case {{code|UTF-8}} ''may'' imply there ''is'' a BOM.<ref>{{cite web |url=https://suika.fam.cx/~wakaba/wiki/sw/n/BOM |title=BOM | work = suikawiki |archive-url=https://web.archive.org/web/20090117052232/https://suika.fam.cx/~wakaba/wiki/sw/n/BOM |archive-date=2009-01-17 |language=ja}}</ref><ref>{{cite web |author-last=Davis |author-first=Mark |author-link=Mark Davis (Unicode) |title=Forms of Unicode |publisher=IBM |url=https://www-128.ibm.com/developerworks/library/utfencodingforms/index.html |access-date=2013-09-18 |archive-url=https://web.archive.org/web/20050506211548/https://www-128.ibm.com/developerworks/library/utfencodingforms/index.html |archive-date=2005-05-06}}</ref> * In Windows, UTF-8 is codepage {{code|65001}}<ref>{{Cite web |url=https://www.dostips.com/forum/viewtopic.php?t=5357 |title=UTF-8 codepage 65001 in Windows 7 - part I |author=Liviu |quote=Previously under XP (and, unverified, but probably Vista, too) for loops simply did not work while codepage 65001 was active |language=en-gb |date=2014-02-07 |access-date=2018-01-30}}</ref> with the symbolic name {{code|CP_UTF8}} in source code. * In MySQL, UTF-8 is called {{code|utf8mb4}},<ref>{{Cite web |title=MySQL :: MySQL 8.0 Reference Manual :: 10.9.1 The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding) |url=https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb4.html |work=MySQL 8.0 Reference Manual |publisher=Oracle Corporation |access-date=2023-03-14}}</ref> while {{code|utf8}} and {{code|utf8mb3}} refer to the obsolete CESU-8 variant.<ref name="mysql3-utf8mb3">{{Cite web |title=MySQL :: MySQL 8.0 Reference Manual :: 10.9.2 The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding) |url=https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb3.html |work=MySQL 8.0 Reference Manual |publisher=Oracle Corporation |access-date=2023-02-24}}</ref> * In Oracle Database, {{code|AL32UTF8}} means UTF-8 (since version 9.0), while {{code|UTF8}} means CESU-8 (since 8.0),<ref>{{Cite web |title=Database Globalization Support Guide |url=https://docs.oracle.com/cd/E11882_01/server.112/e10729/ch6unicode.htm |access-date=2023-03-16 |website=docs.oracle.com |language=en}}</ref> and is not recommended for use.<ref>{{Cite web |last=Hood |first=Doug |date=July 10, 2025 |title=Why the Database Character Set Matters |url=https://blogs.oracle.com/timesten/post/why-databasecharacterset-matters |access-date=2025-11-20 |website=blogs.oracle.com}}</ref> * In HP PCL, the Symbol-ID for UTF-8 is {{code|18N}}.<ref>{{Cite web|url=https://pclhelp.com/pcl-symbol-sets/ |archive-url=https://web.archive.org/web/20150219212843/http://pclhelp.com/pcl-symbol-sets/|url-status=dead|archive-date=2015-02-19|title=HP PCL Symbol Sets {{!}} Printer Control Language (PCL & PXL) Support Blog|date=2015-02-19|access-date=2018-01-30}}</ref>

There are several current definitions of UTF-8 in various standards documents:

* {{IETF RFC|3629|link=no}} / STD 63 (2003), which establishes UTF-8 as a standard internet protocol element * {{IETF RFC|5198|link=no}} defines UTF-8 NFC for Network Interchange (2008) * ISO/IEC 10646:2020/Amd 1:2023<ref>{{Cite web |title=ISO/IEC 10646:2020/Amd 1:2023 |url=https://www.iso.org/standard/83362.html |access-date=2025-11-20 |website=ISO |language=en}}</ref> * ''The Unicode Standard, Version 17.0.0'' (2025)

They supersede the definitions given in the following obsolete works:

* ''The Unicode Standard, Version 2.0'', Appendix A (1996) * ISO/IEC 10646-1:1993 Amendment 2 / Annex R (1996) * {{IETF RFC|2044|link=no}} (1996) * {{IETF RFC|2279|link=no}} (1998) * ''The Unicode Standard, Version 3.0'', §2.3 (2000) plus Corrigendum #1 : UTF-8 Shortest Form (2000) * ''Unicode Standard Annex #27: Unicode 3.1'' (2001)<ref>{{Cite web |title=UAX #27: Unicode 3.1 |url=https://www.unicode.org/reports/tr27/tr27-3.html |access-date=2025-11-20 |website=www.unicode.org}}</ref> * ''The Unicode Standard, Version 5.0'' (2006)<ref>[https://www.unicode.org/versions/Unicode5.0.0/ ''The Unicode Standard, Version 5.0''] [https://www.unicode.org/versions/Unicode5.0.0/ch03.pdf §3.9–§3.10 ch. 3], 2006.</ref> * ''The Unicode Standard, Version 6.0'' (2010)<ref name=":1" />

They are all the same in their general mechanics, with the main differences being on issues such as allowed range of code point values and safe handling of invalid input.

== See also == * {{annotated link|Character encodings in HTML}} * {{annotated link|Comparison of Unicode encodings}} * {{annotated link|GB 18030}} * {{annotated link|Iconv}} * {{annotated link|Unicode and email}} * {{annotated link|Unicode and HTML}} * {{annotated link|UTF-EBCDIC}} * {{annotated link|List of Unicode characters}}

== References == {{reflist}}

== External links == * [https://doc.cat-v.org/plan_9/4th_edition/papers/utf Original UTF-8 paper] ([https://web.archive.org/web/20000917055036/http://plan9.bell-labs.com/sys/doc/utf.pdf or pdf]) for Plan 9 from Bell Labs * [https://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt History of UTF-8 by Rob Pike] * {{YouTube|id=MijmeoH9LT4|title=Characters, Symbols and the Unicode Miracle}}

Category:Character encoding Category:Computer-related introductions in 1993 Category:Encodings Category:Unicode Transformation Formats