Full Width Characters Converter is a browser-based text conversion tool for changing letters, numbers, symbols, spaces, and Japanese Katakana between full-width and half-width forms.
The tool also detects mixed-width text, highlights convertible characters, and provides a character-level change report. All text processing runs directly in the browser.
Website: https://yeshan-jun.github.io/full-width-characters-converter/
- Converts full-width characters to half-width.
- Converts half-width characters to full-width.
- Converts letters, numbers, symbols, spaces, and Japanese Katakana independently.
- Detects mixed full-width and half-width text as the user types.
- Highlights convertible full-width and half-width characters.
- Counts full-width characters, half-width characters, full-width spaces, and half-width Katakana.
- Handles voiced and semi-voiced Katakana such as
ｶﾞ,ﾊﾟ,ガ, andパ. - Shows every changed character, category, and position.
- Copies the converted result to the clipboard.
- Preserves line breaks and unselected character categories.
Paste or type text into the input editor on the left.
The Mixed Width Detector updates automatically and shows:
- Full-width character count
- Half-width character count
- Full-width space count
- Half-width Katakana count
- Highlighted character inspection
Click Use example to load a mixed Japanese text example.
Select the character categories the converter may change:
- Letters
- Numbers
- Symbols
- Spaces
- Katakana
Clear a category to preserve those characters in the result.
Click one of the conversion buttons:
- Convert to Half Width
- Convert to Full Width
The converted text appears in the output editor on the right.
The Change Report shows:
- Original character
- Converted character
- Character category
- Character position
This makes changes such as full-width spaces and Katakana combinations easy to review.
Click Copy result to copy the converted text.
Click Clear to remove the current input and output.
ＡＢＣａｂｃ ↔ ABCabc
１２３４５ ↔ 12345
！＂＃＄％ ↔ !"#$%
Full-width space:
Half-width space:
ガッツポーズ ↔ ｶﾞｯﾂﾎﾟｰｽﾞ
The converter supports half-width Katakana, small Katakana, Japanese punctuation, voiced marks, and semi-voiced marks.
Kanji and Hiragana are preserved because the converter only changes supported character-width pairs.
The project is built with:
- HTML
- CSS
- JavaScript ES modules
- Browser Clipboard API
- Unicode character mapping
- Unicode normalization for Katakana composition
- Node.js built-in test runner
- Python Playwright browser smoke tests
The conversion engine uses targeted character mappings instead of applying compatibility normalization to the entire input.
For Latin letters, numbers, and ASCII symbols, conversion is based on the Unicode offset between half-width ASCII and full-width forms.
For Japanese Katakana:
- Half-width Katakana sequences are composed into full-width Katakana.
- Full-width Katakana is converted through an explicit reverse mapping.
- Voiced and semi-voiced combinations are handled as complete character sequences.
All conversion logic is contained in converter.js and does not require a backend service or external conversion API.
.
├── index.html
├── style.css
├── script.js
├── converter.js
├── favicon.svg
├── package.json
├── tests/
│ ├── converter.test.js
│ ├── html-contract.test.js
│ └── browser_smoke.py
├── .nojekyll
├── .gitignore
├── LICENSE
└── README.md
| File | Purpose |
|---|---|
index.html |
Defines the page structure, SEO metadata, converter controls, examples, footer, and analytics script. |
style.css |
Provides the responsive desktop and mobile interface, editor layout, detector highlights, and component styling. |
script.js |
Connects the page controls to the conversion engine and manages input, output, detector statistics, copy actions, and change reports. |
converter.js |
Contains character mappings, conversion rules, mixed-width detection, highlighting data, and change-report generation. |
favicon.svg |
Provides the website icon. |
package.json |
Defines the project metadata and Node.js test command. |
.nojekyll |
Configures GitHub Pages to serve the repository as a plain static website. |
LICENSE |
Contains the MIT License. |
| File | Purpose |
|---|---|
tests/converter.test.js |
Tests character conversion, category controls, Katakana handling, detection, and change reports. |
tests/html-contract.test.js |
Verifies required HTML controls, SEO metadata, canonical URL, and page structure. |
tests/browser_smoke.py |
Tests the main interaction flow in a real browser. |
This project is a static website and can be deployed without a backend.
-
Create or open the repository:
https://github.com/yeshan-jun/full-width-characters-converter -
Upload the project files to the repository root.
-
Open Settings → Pages.
-
Select Deploy from a branch.
-
Choose the
mainbranch. -
Choose the
/ (root)folder. -
Save the Pages settings.
The website will be available at:
https://yeshan-jun.github.io/full-width-characters-converter/
Run this command inside the project directory:
python -m http.server 8000Then open:
http://127.0.0.1:8000/
A local web server loads the JavaScript ES modules correctly.
The same files can also be deployed to:
- Cloudflare Pages
- Netlify
- Vercel static hosting
- Apache HTTP Server
- Nginx
- Caddy
- Static object storage hosting
GitHub repository:
https://github.com/yeshan-jun/full-width-characters-converter
GitHub Pages website:
https://yeshan-jun.github.io/full-width-characters-converter/
Full Width Characters Converter processes text locally in the browser.
The application does not require an account, backend service, database, or text-processing API. Input text remains in the current browser tab and is cleared when the page is refreshed or closed.
This project is released under the MIT License.