UTF-8: Difference between revisions

UTF-8
Standard	Unicode Standard
Classification	Unicode Transformation Format, extended ASCII, variable-length encoding
Extends	ASCII
Transforms / Encodes	ISO/IEC 10646 (Unicode)
Preceded by	UTF-1
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UTF-8 is a character encoding standard used for electronic communication. Defined by the Unicode Standard, the name is derived from Unicode Transformation Format – 8-bit.^[1] Almost every webpage is stored in UTF-8.

UTF-8 is capable of encoding all 1,112,064^[2] valid Unicode scalar values 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 (including on Microsoft Windows) and this results in fewer internationalization issues than any alternative text encoding.^[3]^[4]

UTF-8 is dominant for all countries/languages on the internet, with 99% global average use, is used in most standards, often the only allowed encoding, and is supported by all modern operating systems and programming languages.

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 0x21–0x7E that meant something else in ASCII, e.g., 0x2F for /, 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)^[5] and most of the text of this proposal were later preserved in the final specification.^[6]^[7]^[8] 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.^[8]^[9] 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,^[10] and then communicated their success back to X/Open, which accepted it as the specification for FSS-UTF.^[8]

UTF-8 was first officially presented at the USENIX conference in San Diego, from January 25 to 29, 1993.^[11] The Internet Engineering Task Force adopted UTF-8 in its Policy on Character Sets and Languages in RFC 2277 (BCP 18) for future internet standards work in January 1998, replacing Single Byte Character Sets such as Latin-1 in older RFCs.^[12]

In November 2003, UTF-8 was restricted by 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 U+10FFFF removed more than 48% of the four-byte sequences and all five- and six-byte sequences.^[13]

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 u to z are replaced by the bits of the code point, from the positions U+uvwxyz:

Code point ↔ UTF-8 conversion
First code point	Last code point	Byte 1	Byte 2	Byte 3	Byte 4
U+0000	U+007F	0yyyzzzz
U+0080	U+07FF	110xxxyy	10yyzzzz
U+0800	U+FFFF	1110wwww	10xxxxyy	10yyzzzz
U+010000	U+10FFFF	11110uvv	10vvwwww	10xxxxyy	10yyzzzz

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.^[14]

This 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 that 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

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 the same code point to be encoded in multiple ways. Overlong encodings (of ../ for example) have been used to bypass security validations in high-profile products including Microsoft's IIS web server^[15] and Apache's Tomcat servlet container.^[16] Overlong encodings should therefore be considered an error and never decoded. Modified UTF-8 allows an overlong encoding of U+0000.

Byte map

The chart below gives the detailed meaning of each byte in a stream encoded in UTF-8.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
0	␀	␁	␂	␃	␄	␅	␆	␇	␈	␉	␊	␋	␌	␍	␎	␏
1	␐	␑	␒	␓	␔	␕	␖	␗	␘	␙	␚	␛	␜	␝	␞	␟
2	␠	!	"	#	$	%	&	'	(	)	*	+	,	-	.	/
3	0	1	2	3	4	5	6	7	8	9	:	;	<	=	>	?
4	@	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O
5	P	Q	R	S	T	U	V	W	X	Y	Z	[	\	]	^	_
6	`	a	b	c	d	e	f	g	h	i	j	k	l	m	n	o
7	p	q	r	s	t	u	v	w	x	y	z	{	\|	}	~	␡
8
9
A
B
C	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2
D	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2
E	3	3	3	3	3	3	3	3	3	3	3	3	3	3	3	3
F	4	4	4	4	4	4	4	4	5	5	5	5	6	6

	ASCII control character
	ASCII character
	Continuation byte
	First byte of a 2-byte code point
	First byte of a 3-byte code point
	First byte of a 4-byte code point
	Unused

Error handling

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

Bytes that never appear in UTF-8: 0xC0, 0xC1, 0xF5–0xFF
A "continuation byte" (0x80–0xBF) at the start of a character
A non-continuation byte (or the string ending) before the end of a character
An overlong encoding (0xE0 followed by less than 0xA0, or 0xF0 followed by less than 0x90)
A 4-byte sequence that decodes to a value greater than U+10FFFF (0xF4 followed by 0x90 or greater)

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 NUL, slash, or quotes, leading to security vulnerabilities. It is also common to throw an exception or truncate the string at an error^[17] 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.^[18]

RFC 3629 states "Implementations of the decoding algorithm MUST protect against decoding invalid sequences."^[19] 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." The standard now recommends replacing each error with the replacement character "�" (U+FFFD) and continue decoding.

Some decoders consider the sequence 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)^[20] 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 E1,A0,20 is a two-byte error followed by a space. This means an error is no more than three bytes long and never contains the start of a valid character, and there are 21,952 different possible errors. Technically this makes UTF-8 no longer a prefix code (you have to read one byte past some errors to figure out they are an error), but searching still works if the searched-for string does not contain any errors.

Making each byte be an error, in which case E1,A0,20 is two errors followed by a space, also still allows searching for a valid string. This means there are only 128 different errors which makes it practical to store the errors in the output string,^[21] 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 1⁄15 chance of starting a valid UTF-8 character. This has the (possibly unintended) 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

Since RFC 3629 (November 2003), the high and low surrogates used by UTF-16 (U+D800 through U+DFFF) are not legal Unicode values, and their UTF-8 encodings must be treated as an invalid byte sequence.^[19] These encodings all start with 0xED followed by 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.^[22] UTF-8 that allows these surrogate halves has been (informally) called WTF-8,^[23] while another variation that also encodes all non-BMP characters as two surrogates (6 bytes instead of 4) is called CESU-8.

Byte-order mark

If the Unicode byte-order mark U+FEFF is at the start of a UTF-8 file, the first three bytes will be 0xEF, 0xBB, 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.^[24] 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).^[25]

Comparison to UTF-16

For a long time there was considerable argument as to whether it was better to process text in UTF-16 or in UTF-8.

The primary advantage of UTF-16 is that the Windows API required it to be used to get access to all Unicode characters (only recently has this been fixed). 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 U+FFFF and combining characters were rarely used, so the 16-bit encoding was fixed-size. This made processing of text more efficient, though the gains are nowhere as great as novice programmers may imagine. All such advantages were lost as soon as UTF-16 became variable width as well.

The code points U+0800–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 the real-world documents due to spaces, newlines, digits, punctuation, English words, and (depending on document format) markup.

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 1/2 the space for any language using mostly Latin letters.

Implementations and adoption

UTF-8 has been the most common encoding for the World Wide Web since 2008.^[27] As of January 2025^[update], UTF-8 is used by 98.5% of surveyed web sites.^[28] 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.^[29] 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)).^[30] UTF-8 is also the recommendation from the WHATWG for HTML and DOM specifications, and stating "UTF-8 encoding is the most appropriate encoding for interchange of Unicode"^[4] and the Internet Mail Consortium recommends that all e‑mail programs be able to display and create mail using UTF-8.^[31]^[32] 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".^[33]

Lots of software has the ability to read/write UTF-8. It may though 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,^[34]^[35]^[36] Microsoft Excel (2016 and later),^[37]^[38] Google Drive, LibreOffice 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.^[39] Windows Notepad, in all currently supported versions of Windows, defaults to writing UTF-8 without a BOM (a change from Windows 7 Notepad), bringing it into line with most other text editors.^[40] Some system files on Windows 11 require UTF-8^[41] with no requirement for a BOM, and almost all files on macOS and Linux are required to be UTF-8 without a BOM.^{[citation needed]} Programming languages that default to UTF-8 for I/O include Ruby 3.0,^[42]^[43] R 4.2.2,^[44] Raku and Java 18.^[45] Although the current version of Python requires an option to open() to read/write UTF-8,^[46] plans exist to make UTF-8 I/O the default in Python 3.15.^[47] C++23 adopts UTF-8 as the only portable source code file format.^[48]

Backwards compatibility is a serious impediment to changing code and APIs using UTF-16 to use UTF-8, but this is happening. As of May 2019^[update], 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,^[49] and even states "UTF-16 [...] is a unique burden that Windows places on code that targets multiple platforms".^[3] The default string primitive in Go,^[50] Julia, Rust, Swift (since version 5),^[51] and PyPy^[52] uses UTF-8 internally in all cases. Python (since version 3.3) uses UTF-8 internally for Python C API extensions^[53]^[54] and sometimes for strings^[53]^[55] and a future version of Python is planned to store strings as UTF-8 by default.^[56]^[57] Modern versions of Microsoft Visual Studio use UTF-8 internally.^[58] Microsoft's SQL Server 2019 added support for UTF-8, and using it results in a 35% speed increase, and "nearly 50% reduction in storage requirements."^[59]

Java internally uses Modified UTF-8 (MUTF-8), in which the null character U+0000 uses the two-byte overlong encoding 0xC0, 0x80, instead of just 0x00.^[60] Modified UTF-8 strings never contain any actual null bytes but can contain all Unicode code points including U+0000,^[61] 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,^[62] but it uses Modified UTF-8 for object serialization,^[63]^[64] for the Java Native Interface,^[65] and for embedding constant strings in class files.^[66] The dex format defined by Dalvik also uses the same modified UTF-8 to represent string values.^[67] Tcl also uses the same modified UTF-8^[68] as Java for internal representation of Unicode data, but uses strict CESU-8 for external data. All known Modified UTF-8 implementations also treat the surrogate pairs as in CESU-8.

Raku programming language (formerly Perl 6) uses utf-8 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 you may want to ensure no normalization is done; for this you can use utf8-c8".^[69] 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.^[70]

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^[71]); 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 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 U+DC80...U+DCFF which are low (trailing) surrogate values and thus "invalid" UTF-16, as used by Python's PEP 383 (or "surrogateescape") approach.^[21] Another encoding called MirBSD OPTU-8/16 converts them to U+EF80...U+EFFF in a Private Use Area.^[72] 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.^[73]

Standards

The official name for the encoding is 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:

Most standards are also case-insensitive and utf-8 is often used.^{[citation needed]}
Web standards (which include CSS, HTML, XML, and HTTP headers) also allow utf8 and many other aliases.^[74]
The official Internet Assigned Numbers Authority lists csUTF8 as the only alias,^[75] which is rarely used.
In some locales UTF-8N means UTF-8 without a byte-order mark (BOM), and in this case UTF-8 may imply there is a BOM.^[76]^[77]
In Windows, UTF-8 is codepage 65001^[78] with the symbolic name CP_UTF8 in source code.
In MySQL, UTF-8 is called utf8mb4,^[79] while utf8 and utf8mb3 refer to the obsolete CESU-8 variant.^[80]
In Oracle Database (since version 9.0), AL32UTF8^[81] means UTF-8, while UTF-8 means CESU-8.
In HP PCL, the Symbol-ID for UTF-8 is 18N.^[82]

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

RFC 3629 / STD 63 (2003), which establishes UTF-8 as a standard internet protocol element
RFC 5198 defines UTF-8 NFC for Network Interchange (2008)
ISO/IEC 10646:2020-1 §9.1 (2020)^[83]
The Unicode Standard, Version 16.0.0 (2024)^[84]

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)
RFC 2044 (1996)
RFC 2279 (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)^[85]
The Unicode Standard, Version 5.0 (2006)^[86]
The Unicode Standard, Version 6.0 (2010)^[87]

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.

References

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^ InputStreamReader and OutputStreamWriter
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^ DataInput and DataOutput
^ "Java Native Interface Specification, chapter 3: JNI Types and Data Structures, section: Modified UTF-8 Strings". Oracle Corporation. 2015. Retrieved 2015-10-16.
^ "The Java Virtual Machine Specification, section 4.4.7: "The CONSTANT_Utf8_info Structure"". Oracle Corporation. 2015. Retrieved 2015-10-16.
^ "ART and Dalvik". Android Open Source Project. Archived from the original on 2013-04-26. Retrieved 2013-04-09.
^ "UTF-8 bit by bit". Tcler's Wiki. 2001-02-28. Retrieved 2022-09-03.
^ "encoding | Raku Documentation". docs.raku.org. Retrieved 2024-10-06.
^ "Unicode | Raku Documentation". docs.raku.org. Retrieved 2024-10-06.
^ "PEP 540 -- Add a new UTF-8 Mode". Python.org. Retrieved 2021-03-24.
^ "RTFM optu8to16(3), optu8to16vis(3)". www.mirbsd.org.
^ Davis, Mark; Suignard, Michel (2014). "3.7 Enabling Lossless Conversion". Unicode Security Considerations. Unicode Technical Report #36.
^ "Encoding Standard § 4.2. Names and labels". WHATWG. Retrieved 2018-04-29.
^ "Character Sets". Internet Assigned Numbers Authority. 2013-01-23. Retrieved 2013-02-08.
^ "BOM". suikawiki (in Japanese). Archived from the original on 2009-01-17.
^ Davis, Mark. "Forms of Unicode". IBM. Archived from the original on 2005-05-06. Retrieved 2013-09-18.
^ Liviu (2014-02-07). "UTF-8 codepage 65001 in Windows 7 - part I". Retrieved 2018-01-30. Previously under XP (and, unverified, but probably Vista, too) for loops simply did not work while codepage 65001 was active
^ "MySQL :: MySQL 8.0 Reference Manual :: 10.9.1 The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)". MySQL 8.0 Reference Manual. Oracle Corporation. Retrieved 2023-03-14.
^ "MySQL :: MySQL 8.0 Reference Manual :: 10.9.2 The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)". MySQL 8.0 Reference Manual. Oracle Corporation. Retrieved 2023-02-24.
^ "Database Globalization Support Guide". docs.oracle.com. Retrieved 2023-03-16.
^ "HP PCL Symbol Sets | Printer Control Language (PCL & PXL) Support Blog". 2015-02-19. Archived from the original on 2015-02-19. Retrieved 2018-01-30.
^ ISO/IEC 10646:2020 §9.1, 2020.
^ The Unicode Standard, Version 16.0 §3.9 D92, §3.10 D95, 2021.
^ Unicode Standard Annex #27: Unicode 3.1, 2001.
^ The Unicode Standard, Version 5.0 §3.9–§3.10 ch. 3, 2006.
^ The Unicode Standard, Version 6.0 §3.9 D92, §3.10 D95, 2010.

External links

[1] "Chapter 2. General Structure". The Unicode Standard (6.0 ed.). Mountain View, California, US: The Unicode Consortium. ISBN 978-1-936213-01-6.

[2] "Conformance". The Unicode Standard (6.0 ed.). Mountain View, California, US: The Unicode Consortium. D76 Unicode scalar value. ISBN 978-1-936213-01-6. – 17 planes times 2¹⁶ code points per plane, minus 2¹¹ technically-invalid surrogates

[Microsoft_GDK-3] "UTF-8 support in the Microsoft GDK". Microsoft Learn. Microsoft Game Development Kit (GDK). Retrieved 2023-03-05.

[whatwg-4] "Encoding Standard". encoding.spec.whatwg.org. Retrieved 2020-04-15.

[5] "File System Safe UCS — Transformation Format (FSS-UTF) - X/Open Preliminary Specification" (PDF). unicode.org.

[FSS-UTF-6] "Appendix F. FSS-UTF / File System Safe UCS Transformation format" (PDF). The Unicode Standard 1.1. Archived (PDF) from the original on 2016-06-07. Retrieved 2016-06-07.

[Whistler_2001-7] Whistler, Kenneth (2001-06-12). "FSS-UTF, UTF-2, UTF-8, and UTF-16". Archived from the original on 2016-06-07. Retrieved 2006-06-07.

[pikeviacambridge-8] Pike, Rob (2003-04-30). "UTF-8 history". Retrieved 2012-09-07.

[9] At that time subtraction was slower than bit logic on many computers, and speed was considered necessary for acceptance.^{[citation needed]}

[10] Pike, Rob; Thompson, Ken (1993). "Hello World or Καλημέρα κόσμε or こんにちは世界" (PDF). Proceedings of the Winter 1993 USENIX Conference.

[11] "USENIX Winter 1993 Conference Proceedings". usenix.org.

[rfc2277-12] Alvestrand, Harald T. (January 1998). IETF Policy on Character Sets and Languages. IETF. doi:10.17487/RFC2277. BCP 18. RFC 2277.

[13] Pike, Rob (2012-09-06). "UTF-8 turned 20 years old yesterday". Retrieved 2012-09-07.

[problems_of_only_BMP-14] Lunde, Ken (2022-01-09). "2022 Top Ten List: Why Support Beyond-BMP Code Points?". Medium. Retrieved 2024-01-07.

[MS00-078-15] Marin, Marvin (2000-10-17). Windows NT UNICODE vulnerability analysis. Web server folder traversal. SANS Institute (Report). Malware FAQ. MS00-078. Archived from the original on Aug 27, 2014.

[CVE-2008-2938-16] "CVE-2008-2938". National Vulnerability Database (nvd.nist.gov). U.S. National Institute of Standards and Technology. 2008.

[17] "DataInput". docs.oracle.com. Java Platform SE 8. Retrieved 2021-03-24.

[PEP383-18] "Non-decodable bytes in system character interfaces". python.org. 2009-04-22. Retrieved 2014-08-13.

[rfc3629-19] Yergeau, F. (November 2003). UTF-8, a transformation format of ISO 10646. IETF. doi:10.17487/RFC3629. STD 63. RFC 3629. Retrieved August 20, 2020.

[20] Unicode 6.0.0. unicode.org (Report). October 2010.

[pep383-21] von Löwis, Martin (2009-04-22). "Non-decodable Bytes in System Character Interfaces". Python Software Foundation. PEP 383.

[PEP_529-22] "Change Windows filesystem encoding to UTF-8". Python.org. PEP 529. Retrieved 2022-05-10.

[wtf-8-23] "The WTF-8 encoding".

[24] "Chapter 2" (PDF), The Unicode Standard — Version 15.0.0, p. 39

[25] "UTF-8 and Unicode FAQ for Unix/Linux".

[MarkDavis2012-26] Davis, Mark (2012-02-03). "Unicode over 60 percent of the web". Official Google blog. Archived from the original on 2018-08-09. Retrieved 2020-07-24.

[markdavis-27] Davis, Mark (2008-05-05). "Moving to Unicode 5.1". Official Google blog. Retrieved 2023-03-13.

[W3TechsWebEncoding-28] "Usage Survey of Character Encodings broken down by Ranking". W3Techs. January 2025. Retrieved 2025-01-07.

[29] "Usage statistics and market share of ASCII for websites". W3Techs. January 2025. Retrieved 2025-01-07.

[rfc8259-30] Bray, Tim (December 2017). Bray, Tim (ed.). The JavaScript Object Notation (JSON) Data Interchange Format. IETF. doi:10.17487/RFC8259. RFC 8259. Retrieved 16 February 2018.

[IMC-31] "Using International Characters in Internet Mail". Internet Mail Consortium. 1998-08-01. Archived from the original on 2007-10-26. Retrieved 2007-11-08.

[mandatory-32] "Encoding Standard". encoding.spec.whatwg.org. Retrieved 2018-11-15.

[html5charset-33] "Specifying the document's character encoding". HTML 5.2 (Report). World Wide Web Consortium. 14 December 2017. Retrieved 2018-06-03.

[34] "Choose text encoding when you open and save files". Microsoft Support (support.microsoft.com). Retrieved 2021-11-01.

[35] "UTF-8 - Character encoding of Microsoft Word DOC and DOCX files?". Stack Overflow. Retrieved 2021-11-01.

[36] "Exporting a UTF-8 .txt file from Word". support.3playmedia.com. 14 March 2023.

[37] "Are XLSX files UTF-8 encoded, by definition?". Stack Overflow. Excel. Retrieved 2021-11-01.

[38] Abhinav, Ankit; Xu, Jazlyn (April 13, 2020). "How to open UTF-8 CSV file in Excel without mis-conversion of characters in Japanese and Chinese language for both Mac and Windows?". Microsoft Support Community. Retrieved 2021-11-01.

[39] Galloway, Matt (October 2012). "Character encoding for iOS developers; or, UTF-8 what now?". www.galloway.me.uk. Retrieved 2021-01-02. ... in reality, you usually just assume UTF-8 since that is by far the most common encoding.

[40] "Windows 10 Notepad is getting better UTF-8 encoding support". BleepingComputer. Retrieved 2021-03-24. Microsoft is now defaulting to saving new text files as UTF-8 without BOM, as shown below.

[41] "Customize the Windows 11 Start menu". docs.microsoft.com. Retrieved 2021-06-29. Make sure your LayoutModification.json uses UTF-8 encoding.

[42] "Set default for Encoding.default_external to UTF-8 on Windows". Ruby Issue Tracking System (bugs.ruby-lang.org). Ruby master. Feature #16604. Retrieved 2022-08-01.

[43] "Feature #12650: Use UTF-8 encoding for ENV on Windows". Ruby Issue Tracking System (bugs.ruby-lang.org). Ruby master. Retrieved 2022-08-01.

[44] "New features in R 4.2.0". R bloggers (r-bloggers.com). The Jumping Rivers Blog. 2022-04-01. Retrieved 2022-08-01.

[Java_UTF-8_and_UTF-16-45] "UTF-8 by default". openjdk.java.net. JEP 400. Retrieved 2022-03-30.

[46] "add a new UTF-8 mode". peps.python.org. PEP 540. Retrieved 2022-09-23.

[47] "Make UTF-8 mode default". peps.python.org. PEP 686. Retrieved 2023-07-26.

[48] Support for UTF-8 as a portable source file encoding (PDF). open-std.org (Report). 2022. p2295r6.

[Microsoft-UTF-8-49] "Use UTF-8 code pages in Windows apps". Microsoft Learn. 20 August 2024. Retrieved 2024-09-24.

[50] "Source code representation". The Go Programming Language Specification. golang.org (Report). Retrieved 2021-02-10.

[51] Tsai, Michael J. (21 March 2019). "UTF-8 string in Swift 5" (blog post). Retrieved 2021-03-15.

[52] "PyPy v7.1 released; now uses UTF-8 internally for Unicode strings". Mattip. PyPy status blog. 2019-03-24. Retrieved 2020-11-21.

[PEP393-53] "Flexible String Representation". Python.org. PEP 393. Retrieved 2022-05-18.

[54] "Common Object Structures". Python documentation. Retrieved 2024-05-29.

[55] "Unicode objects and codecs". Python documentation. Retrieved 2023-08-19. UTF-8 representation is created on demand and cached in the Unicode object.

[56] "PEP 623 – remove wstr from Unicode". Python.org. Retrieved 2020-11-21.

[57] Wouters, Thomas (2023-07-11). "Python 3.12.0 beta 4 released". Python Insider (pythoninsider.blogspot.com) (blog post). Retrieved 2023-07-26. The deprecated wstr and wstr_length members of the C implementation of unicode objects were removed, per PEP 623.

[58] "validate-charset (validate for compatible characters)". docs.microsoft.com. Retrieved 2021-07-19. Visual Studio uses UTF-8 as the internal character encoding during conversion between the source character set and the execution character set.

[59] "Introducing UTF-8 support for SQL Server". techcommunity.microsoft.com. 2019-07-02. Retrieved 2021-08-24.

[60] "Java SE documentation for Interface java.io.DataInput, subsection on Modified UTF-8". Oracle Corporation. 2015. Retrieved 2015-10-16.

[61] "The Java Virtual Machine Specification, section 4.4.7: "The CONSTANT_Utf8_info Structure"". Oracle Corporation. 2015. Retrieved 2015-10-16.

[62] InputStreamReader and OutputStreamWriter

[63] "Java Object Serialization Specification, chapter 6: Object Serialization Stream Protocol, section 2: Stream Elements". Oracle Corporation. 2010. Retrieved 2015-10-16.

[64] DataInput and DataOutput

[65] "Java Native Interface Specification, chapter 3: JNI Types and Data Structures, section: Modified UTF-8 Strings". Oracle Corporation. 2015. Retrieved 2015-10-16.

[66] "The Java Virtual Machine Specification, section 4.4.7: "The CONSTANT_Utf8_info Structure"". Oracle Corporation. 2015. Retrieved 2015-10-16.

[67] "ART and Dalvik". Android Open Source Project. Archived from the original on 2013-04-26. Retrieved 2013-04-09.

[68] "UTF-8 bit by bit". Tcler's Wiki. 2001-02-28. Retrieved 2022-09-03.

[69] "encoding | Raku Documentation". docs.raku.org. Retrieved 2024-10-06.

[70] "Unicode | Raku Documentation". docs.raku.org. Retrieved 2024-10-06.

[71] "PEP 540 -- Add a new UTF-8 Mode". Python.org. Retrieved 2021-03-24.

[72] "RTFM optu8to16(3), optu8to16vis(3)". www.mirbsd.org.

[davis383-73] Davis, Mark; Suignard, Michel (2014). "3.7 Enabling Lossless Conversion". Unicode Security Considerations. Unicode Technical Report #36.

[74] "Encoding Standard § 4.2. Names and labels". WHATWG. Retrieved 2018-04-29.

[IANA_2013_CS-75] "Character Sets". Internet Assigned Numbers Authority. 2013-01-23. Retrieved 2013-02-08.

[76] "BOM". suikawiki (in Japanese). Archived from the original on 2009-01-17.

[77] Davis, Mark. "Forms of Unicode". IBM. Archived from the original on 2005-05-06. Retrieved 2013-09-18.

[78] Liviu (2014-02-07). "UTF-8 codepage 65001 in Windows 7 - part I". Retrieved 2018-01-30. Previously under XP (and, unverified, but probably Vista, too) for loops simply did not work while codepage 65001 was active

[79] "MySQL :: MySQL 8.0 Reference Manual :: 10.9.1 The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)". MySQL 8.0 Reference Manual. Oracle Corporation. Retrieved 2023-03-14.

[mysql3-utf8mb3-80] "MySQL :: MySQL 8.0 Reference Manual :: 10.9.2 The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)". MySQL 8.0 Reference Manual. Oracle Corporation. Retrieved 2023-02-24.

[81] "Database Globalization Support Guide". docs.oracle.com. Retrieved 2023-03-16.

[82] "HP PCL Symbol Sets | Printer Control Language (PCL & PXL) Support Blog". 2015-02-19. Archived from the original on 2015-02-19. Retrieved 2018-01-30.

[83] ISO/IEC 10646:2020 §9.1, 2020.

[84] The Unicode Standard, Version 16.0 §3.9 D92, §3.10 D95, 2021.

[85] Unicode Standard Annex #27: Unicode 3.1, 2001.

[86] The Unicode Standard, Version 5.0 §3.9–§3.10 ch. 3, 2006.

[87] The Unicode Standard, Version 6.0 §3.9 D92, §3.10 D95, 2010.

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v t e Character encodings
Early telecommunications	Telegraph code Needle Morse Non-Latin Wabun/Kana Chinese Cyrillic Baudot and Murray Fieldata ASCII ISO/IEC 646 BCDIC Teletex and Videotex/Teletext T.51/ISO/IEC 6937 ITU T.61 ITU T.101 World System Teletext background sets Transcode
ISO/IEC 8859	Approved parts -1 (Western Europe) -2 (Central Europe) -3 (Maltese/Esperanto) -4 (North Europe) -5 (Cyrillic) -6 (Arabic) -7 (Greek) -8 (Hebrew) -9 (Turkish) -10 (Nordic) -11 (Thai) -13 (Baltic) -14 (Celtic) -15 (New Western Europe) -16 (Romanian) Abandoned parts -12 (Devanagari) Proposed but not approved KOI-8 Cyrillic Sámi Adaptations Welsh Barents Cyrillic Estonian Ukrainian Cyrillic
Bibliographic use	MARC-8 ANSEL CCCII/EACC ISO 5426 5426-2 5427 5428 6438 6862
National standards	ArmSCII Big5 BraSCII CNS 11643 DIN 66003 ELOT 927 GOST 10859 GB 2312 GB 12345 GB 12052 GB 18030 HKSCS ISCII JIS X 0201 JIS X 0208 JIS X 0212 JIS X 0213 KOI-7 KPS 9566 KS X 1001 KS X 1002 LST 1564 LST 1590-4 PASCII Shift JIS SI 960 TIS-620 TSCII VISCII VSCII YUSCII
ISO/IEC 2022	ISO/IEC 8859 ISO/IEC 10367 Extended Unix Code / EUC
Mac OS Code pages ("scripts")	Armenian Arabic Barents Cyrillic Celtic Central European Croatian Cyrillic Devanagari Farsi (Persian) Font X (Kermit) Gaelic Georgian Greek Gujarati Gurmukhi Hebrew Iceland Inuit Keyboard Latin (Kermit) Maltese/Esperanto Ogham Roman Romanian Sámi Turkish Turkic Cyrillic Ukrainian VT100
DOS code pages	437 668 708 720 737 770 773 775 776 777 778 850 851 852 853 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 897 899 903 904 932 936 942 949 950 951 1040 1042 1043 1046 1098 1115 1116 1117 1118 1127 3846 ABICOMP CS Indic CSX Indic CSX+ Indic CWI-2 Iran System Kamenický Mazovia MIK
IBM AIX code pages	895 896 912 915 921 922 1006 1008 1009 1010 1012 1013 1014 1015 1016 1017 1018 1019 1046 1124 1133
Windows code pages	CER-GS 932 936 (GBK) 950 1169 Extended Latin-8 1250 1251 1252 1253 1254 1255 1256 1257 1258 1270 Cyrillic + Finnish Cyrillic + French Cyrillic + German Polytonic Greek
EBCDIC code pages	Japanese language in EBCDIC DKOI
DEC terminals (VTx)	Multinational (MCS) National Replacement (NRCS) French Canadian Swiss Spanish United Kingdom Dutch Finnish French Norwegian and Danish Swedish Norwegian and Danish (alternative) 8-bit Greek 8-bit Turkish SI 960 Hebrew Special Graphics Technical (TCS)
Platform specific	1052 1053 1054 1055 1056 1057 1058 Acorn RISC OS Amstrad CPC Apple II ATASCII Atari ST BICS Casio calculators CDC Compucolor 8001 Compucolor II CP/M+ DEC RADIX 50 DEC MCS/NRCS DG International Galaksija GEM GSM 03.38 HP Roman HP FOCAL HP RPL SQUOZE LICS LMBCS MSX NEC APC NeXT PETSCII PostScript Standard PostScript Latin 1 SAM Coupé Sega SC-3000 Sharp calculators Sharp MZ Sinclair QL Teletext TI calculators TRS-80 Ventura International WISCII XCCS ZX80 ZX81 ZX Spectrum
Unicode / ISO/IEC 10646	UTF-1 UTF-7 UTF-8 UTF-16 UTF-32 UTF-EBCDIC GB 18030 DIN 91379 BOCU-1 CESU-8 SCSU TACE16 Comparison of Unicode encodings
TeX typesetting system	Cork LY1 OML OMS OT1
Miscellaneous code pages	ABICOMP ASMO 449 Digital encoding of APL symbols ISO-IR-68 ARIB STD-B24 Fieldata HZ IEC-P27-1 INIS 7-bit 8-bit ISO-IR-169 ISO 2033 KOI KOI8-R KOI8-RU KOI8-U Mojikyō SEASCII Stanford/ITS Symbol TRON Unified Hangul Code
Control character	Morse prosigns C0 and C1 control codes ISO/IEC 6429 JIS X 0211 Unicode control, format and separator characters Whitespace characters
Related topics	CCSID Character encodings in HTML Charset detection Han unification Hardware code page MICR code Mojibake Variable-length encoding
Character sets

v t e Rob Pike
Operating systems	Plan 9 from Bell Labs Inferno
Programming languages	Newsqueak Limbo Sawzall Go
Software	acme Blit sam rio 8½
Publications	The Practice of Programming The Unix Programming Environment
Other	Renée French Mark V. Shaney UTF-8

v t e Ken Thompson
Operating systems	Unix Plan 9 from Bell Labs Inferno
Programming languages	B Go
Software	Belle ed grep sam Space Travel Thompson shell
Associated institutions	Bell Labs Google
Other	UTF-8