apanese Writing Proofreader | Free Online Grammar & Style Checker

What is the Japanese Writing Proofreader?

This tool automatically checks Japanese text for typos, grammar errors, redundant expressions, and style inconsistencies entirely within your browser. Since text is processed locally via JavaScript and never sent to any server, confidential documents are completely safe.

Features 12+ proofreading rules with individual ON/OFF toggles, writing style detection (polite vs. plain), sentence length limits, and particle duplication checks.

Use Cases

How to Use

1. Enter text — Type, paste, or drag & drop a .txt file. Try preset samples.
2. Configure rules — Select style check mode and max sentence length. Toggle individual rules.
3. 🔍 Run Check — Click the button or press Ctrl+Enter. Errors are highlighted inline.
4. Review results — Check score, text statistics, and click error items to jump to the spot.

Japanese Proofreading Glossary

Ra-nuki kotoba (ら抜き言葉)

A colloquial contraction of potential verb forms that drops the 'ra' syllable: "見れる" (mireru) instead of "見られる" (mirareru). Accepted in casual speech but flagged in formal writing.

Jōtai / Keitai (常体/敬体)

Two fundamental Japanese writing styles. Keitai (desu/masu) is polite; jōtai (da/dearu) is plain. Mixing them in one document is considered poor style.

Joshi (助詞) — Particles

Function words like が, の, を, に that indicate grammatical relationships. Repeated use of the same particle in a sentence makes text awkward.

Kanji Ratio (漢字含有率)

The percentage of kanji characters in text. 30–50% is generally considered readable; too high feels dense, too low feels childish.

How Browser-Side Proofreading Works

All checking is done in client-side JavaScript. No API calls, no server uploads. The engine uses regex-based pattern matching and simple morphological analysis.

Processing Flow

1. Input — User enters or imports text
2. Sentence splitting — Split at 。!? boundaries
3. Rule evaluation — Apply 12+ regex/pattern rules
4. Error collection — Gather offsets, messages, severity
5. Highlight + Score — Overlay wavy underlines, compute score

Frequently Asked Questions

Which browsers are supported?

Chrome, Edge, Safari, Firefox. Pure JavaScript — no browser-specific limitations.

Is there a character limit?

No. All processing is local. Very long texts (50K+) may take a moment.

Is my text sent to a server?

No. Everything runs in your browser. Auto-save uses only localStorage.

Does it check English text?

This tool is specialized for Japanese. For English, try Grammarly or LanguageTool.