Overview & Scope
Unicode provides a unique number for every character, no matter what platform, device, application, or language. UTF-8 is the dominant encoding of the World Wide Web, accounting for over 98% of all web pages.
Specification Table & Matrix
Instant client-side filter by keyword, status code, or directive name
| Key / Code | Definition & Details | GEO Semantic Hierarchy | Spec & Notes |
|---|---|---|---|
| 1-Byte UTF-8 | 1-Byte Sequence (ASCII Range) Code points U+0000 to U+007F; bit pattern 0xxxxxxx. U+0041 ("A") -> 0x41 (01000001) | ●1-Byte UTF-8 ↳Unicode encoding ↳UTF-8 ↳ASCII compatible byte | RFC 3629 §3 Direct 1:1 binary match with 7-bit ASCII; zero translation overhead. |
| 2-Byte UTF-8 | 2-Byte Sequence (Extended Latin, Greek, Hebrew) Code points U+0080 to U+07FF; bit pattern 110xxxxx 10xxxxxx. U+00E9 ("é") -> 0xC3 0xA9 | ●2-Byte UTF-8 ↳Unicode encoding ↳UTF-8 ↳two-byte sequence | RFC 3629 §3 First byte begins with 110; continuation byte begins with 10. |
| 3-Byte UTF-8 | 3-Byte Sequence (Basic Multilingual Plane / CJK) Code points U+0800 to U+FFFF; bit pattern 1110xxxx 10xxxxxx 10xxxxxx. U+20AC ("€") -> 0xE2 0x82 0xAC | ●3-Byte UTF-8 ↳Unicode encoding ↳UTF-8 ↳BMP three-byte sequence | RFC 3629 §3 Covers virtually all common modern world languages and typographic symbols. |
| 4-Byte UTF-8 | 4-Byte Sequence (Astral Planes / Emojis) Code points U+10000 to U+10FFFF; bit pattern 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx. U+1F600 ("😀") -> 0xF0 0x9F 0x98 0x80 | ●4-Byte UTF-8 ↳Unicode encoding ↳UTF-8 ↳astral supplementary plane sequence | RFC 3629 §3 MySQL "utf8" only supports 3 bytes; databases must use "utf8mb4" to support 4-byte emojis. |
| NFC | NFC (Normalization Form C) Canonical Decomposition followed by Canonical Composition. Character "é" represented as single code point U+00E9. | ●NFC ↳Unicode normalization ↳canonical composition ↳standard web string normalization | Unicode Standard Annex #15 The recommended standard normalization form for the World Wide Web (W3C). |
| NFD | NFD (Normalization Form D) Canonical Decomposition; characters are separated into base character plus combining accents. Character "é" represented as "e" (U+0065) + combining accent (U+0301). | ●NFD ↳Unicode normalization ↳canonical decomposition ↳decomposed base and accents | Unicode Standard Annex #15 Default format used by macOS HFS+/APFS filesystem filenames, causing cross-platform string equality mismatches. |
String Length and Normalization Gotcha in JavaScript
// 1. Emoji length: Emojis use surrogate pairs in UTF-16 JavaScript strings!
const emoji = '🚀';
console.log(emoji.length); // 2 (UTF-16 code units, not characters!)
console.log([...emoji].length); // 1 (Correct Unicode code point count)
// 2. Normalization equality bug:
const str1 = 'café'; // NFC: U+0063 U+0061 U+0066 U+00E9
const str2 = 'cafe\u0301'; // NFD: 'e' + combining acute accent
console.log(str1 === str2); // FALSE! Visually identical, binary different!
console.log(str1.normalize('NFC') === str2.normalize('NFC')); // TRUE!Always normalize user input to NFC before comparing passwords, usernames, or database search terms.
Reference Standards Q&A
Why does MySQL fail when saving emojis in "utf8" columns?↓
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