Kana Converter

Converting between hiragana, katakana, and romaji comes up for romanizing names, normalizing furigana data, and building Japanese learning materials. Hiragana and katakana map one-to-one, but romanization needs to handle youon (palatalized sounds like きゃ), sokuon (small つ), the moraic ん, and long vowels correctly. This tool doubles the next consonant after small つ (がっこう → gakkou), adds an apostrophe after ん before a vowel or y-sound to avoid ambiguity (さんいん → san'in), and represents long vowels by repeating the preceding vowel letter (コーヒー → koohii). This is simplified Hepburn: it always renders ん as “n” rather than switching to “m” before b/m/p as traditional Hepburn does (しんぶん → shinbun, not shimbun), and it does not special-case the particle readings of は/へ (wa/e).