Unicode Converter

Unicode is an industry standard in computing that encodes most of the world's writing systems. Each Unicode character has a unique numeric identifier called a Code Point, typically represented in hexadecimal with a U+ prefix, such as U+4E2D for the Chinese character '中'. The Unicode Converter tool can convert text to various Unicode representation formats and also restore Unicode encodings back to text. Unicode describes characters by code points, while encodings such as UTF-8 define how those code points are stored as bytes. This matters when analyzing text with emoji, accents, CJK characters, symbols, control characters, or mixed scripts. One visible character may consist of multiple code points, especially with combining marks, variation selectors, or emoji sequences. The tool helps debug mojibake, normalization, escape sequences, invisible characters, and mismatches between character count and byte length.

The Unicode Standard (ISO/IEC 10646) assigns a unique numeric code point to every character across 17 planes (U+0000 to U+10FFFF). The Basic Multilingual Plane (BMP, Plane 0) covers U+0000–U+FFFF and contains nearly all modern writing systems including CJK Unified Ideographs. Supplementary planes (1–16) hold historic scripts, rare CJK, emoji, and special-purpose characters. The tool converts between readable text and two machine-oriented representations: JavaScript-style \uXXXX escape sequences and the standard U+XXXX notation. UTF-16 is the internal encoding of JavaScript strings — every BMP character is stored as a single 16-bit code unit equal to its code point, while supplementary characters (U+10000 and above) are encoded as surrogate pairs: 0x10000 is subtracted from the code point to leave a 20-bit value, which is then split into a 10-bit high surrogate (0xD800 + ((cp - 0x10000) >> 10)) and a 10-bit low surrogate (0xDC00 + ((cp - 0x10000) & 0x3FF)). The tool's encode mode detects supplementary code points via String.prototype.codePointAt() and generates the correct two-\u escape for the \uXXXX format. For U+XXXX format, the full code point is displayed directly. The decode mode parses three syntaxes: \uXXXX (four hex digits, BMP only), \u{XXXXX} (ES6 curly-brace syntax supporting the full Unicode range), and U+XXXX (the standard notation with variable-length hex). The regex /\\u\{([0-9a-fA-F]+)\}/g handles curly-brace escapes and feeds them to String.fromCodePoint(), while /\\u([0-9a-fA-F]{4})/g handles traditional escapes via String.fromCharCode(). Mixing the two correctly reconstructs surrogate pairs when a supplementary character was encoded as two \u escapes. UTF-8 encoding is relevant because it determines byte length: a BMP character like '中' (U+4E2D) encodes as 3 UTF-8 bytes (E4 B8 AD), while an emoji like '😀' (U+1F600) requires 4 bytes (F0 9F 98 80). The tool's character counter distinguishes between code point count and UTF-16 code unit count — a useful distinction when debugging length limits in databases, APIs, or form fields that count code units rather than characters.

• Code point iteration: String.prototype.codePointAt(pos) correctly returns the full code point for supplementary characters, unlike charCodeAt() which returns only the high surrogate — the tool uses the spread operator [...str] to iterate by code point, which internally calls the string iterator protocol.
• Surrogate pair math: For a supplementary code point CP > 0xFFFF, the high surrogate is Math.floor((CP - 0x10000) / 0x400) + 0xD800 and the low surrogate is ((CP - 0x10000) % 0x400) + 0xDC00 — the encode mode applies this formula to produce valid \uD800\uDC00 pairs.
• Decode regex pipeline: Three patterns run sequentially — \u{XXXXX} (ES6 curly braces) → \uXXXX (four-digit hex) → U+XXXX (standard notation) — with fromCodePoint() handling the curly-brace and U+ paths and fromCharCode() handling the traditional four-digit path.
• UTF-8 byte structure: BMP characters use 1–3 UTF-8 bytes (ASCII = 1 byte, Latin supplement = 2 bytes, CJK = 3 bytes); supplementary characters use 4 bytes following the pattern 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx — the tool's byte counter uses new Blob([str]).size for accurate measurement.
• Code point vs code unit: A single visible character may occupy multiple code points (e.g., é can be U+00E9 or U+0065 + U+0301 combining acute) — the tool reports both charCount (UTF-16 code units) and codepointCount (Unicode scalar values) to surface this discrepancy.
• Unicode planes overview: Plane 0 (BMP) = modern scripts, Plane 1 (SMP) = historic + emoji + math, Plane 2 (SIP) = rare CJK, Plane 14 (SSP) = tags + variation selectors, Planes 15–16 = private use — the encode mode correctly handles all planes via codePointAt().
• \u vs U+ notation: \uXXXX is the JavaScript/Java/C escape sequence (BMP only without curly braces); U+XXXX is the Unicode Consortium's canonical notation (minimum 4 hex digits, no upper limit) — the tool's format toggle switches between these representations.