Full-Width Half-Width Converter — Japanese Text Normalizer

A free online tool that normalizes Japanese text by unifying full-width/half-width characters, katakana/hiragana, and whitespace. Perfect for form input preprocessing, data cleansing, and text proofreading.

Includes 5 presets (Form Input, Alphanumerics Half-width, Kana Full-width, All Hiragana, All Katakana) plus advanced individual settings for alphanumerics, symbols, spaces, kana width, kana type, line endings, trailing whitespace, and tab conversion. A diff highlighting feature lets you visually review all changes.

All processing runs entirely in your browser — your data is never uploaded to any server. No registration, no installation. Just paste your text and start normalizing instantly.

Full-width Alphanumerics

Characters like Ａ-Ｚ, ａ-ｚ, ０-９ that occupy the same width as CJK characters. Entered when the Japanese IME is active, they are typically converted to half-width (A-Z, a-z, 0-9) for web and data processing.

Half-width Katakana

Narrow katakana characters like ｱ-ﾝ from legacy Japanese computing. In modern Unicode environments, they are normalized to full-width katakana (ア-ン). NFKC normalization also converts them.

Full-width Space

The ideographic space (U+3000) entered via Japanese input. Since web technologies use half-width spaces (U+0020), mixed spaces can cause bugs or layout issues.

Normalization

The process of unifying text variations. Includes full/half-width conversion, katakana/hiragana conversion, and line ending unification. Improves consistency for search, matching, and data processing.

NFKC (Unicode Normalization)

A Unicode normalization form that maps compatibility-equivalent characters to canonical forms. Converts full-width alphanumerics to half-width, half-width kana to full-width, and more.

Line Ending

Control characters marking line breaks. LF (\n, Unix/macOS standard) and CRLF (\r\n, Windows standard). Mixing them causes processing errors.

Trim

Removing whitespace from the beginning and end of strings. Used to clean invisible spaces at line ends or around text blocks.

Character Code Conversion

Full-width ↔ half-width conversion uses Unicode code point offset calculation. Full-width alphanumerics (U+FF10–U+FF5A) differ from half-width (U+0030–U+007A) by a fixed offset of 0xFEE0, enabling fast arithmetic conversion. Symbols use the same offset method.

Kana Conversion Algorithm

Half-width → full-width kana uses Unicode NFKC normalization. Voiced/semi-voiced half-width kana (e.g., ｶﾞ = 2 characters) are correctly merged into single full-width characters (ガ). Reverse conversion uses NFD decomposition to separate dakuten marks, then maps through a conversion table.

Diff Display (Myers Algorithm)

The diff view uses the Myers diff algorithm with O(ND) character-level comparison, highlighting deletions (red) and insertions (green). For performance, diff computation is skipped for texts exceeding 6,000 characters.

Q. How do I convert full-width alphanumerics to half-width?

A. Select the "Alphanumerics → Half-width only" preset. This converts only alphanumerics and symbols to half-width while keeping katakana and hiragana unchanged.

Q. How do I convert half-width katakana to full-width?

A. Select the "Half-width ｶﾅ → Full-width only" preset. Voiced/semi-voiced half-width kana (ｶﾞ, ﾊﾟ, etc.) are correctly merged into single full-width characters.

Q. Can I convert between katakana and hiragana?

A. Yes. Use the "All to Hiragana" or "All to Katakana" presets, or set "Kana Type" individually in Advanced Options.

Q. Is my data sent to any server?

A. No. All processing runs in your browser's JavaScript engine. Your text data is never transmitted to any server.

Q. Does it work on mobile devices?

A. Yes. The tool is fully responsive and works on smartphones and tablets.

Q. Why doesn't the diff view appear?

A. Diff computation is automatically skipped for texts over 6,000 characters for performance reasons. Shorten your text or disable diff display.

Q. What happens if I change preset settings manually?

A. The preset automatically switches to "Custom" when you modify individual options. Your custom settings are preserved across visits (via localStorage).