Full-width / half-width converter

What is this full-width / half-width converter?

A free, browser-based tool that converts text between full-width (全角) and half-width (半角) forms. Choose which character classes to convert — ASCII letters and symbols, digits only, or katakana — and switch the direction with a single toggle. Half-width katakana with combining dakuten / handakuten marks is handled correctly (ｶﾞ ↔ ガ). Everything runs locally in your browser, so your text is never uploaded.

How to use it

1. Type or paste your text into the box on the left.
2. Pick the direction — Full → Half or Half → Full.
3. Check the character classes you want to convert (ASCII, digits, katakana).
4. Copy the result or download it as a text file.

Common use cases

• Normalizing full-width digits and symbols in phone numbers, postal codes, or order IDs before a CSV import.
• Cleaning half-width katakana from legacy systems into readable full-width katakana.
• Standardizing form input so duplicate detection and matching work reliably.

Other list tools

• Character counter
• Date normalizer
• Phone normalizer
• Newlines to CSV