Best Japanese Grammar Checkers in 2026 — Tools for Kanji, Hiragana & Katakana

Why Japanese Grammar Checking Is Unique

English grammar checkers rely on spaces between words, subject-verb agreement, and tense patterns. Japanese breaks all of those assumptions. Here's what makes it fundamentally different:

• Three writing systems — Japanese mixes kanji (漢字), hiragana (ひらがな), and katakana (カタカナ) in the same sentence. A grammar checker must parse all three correctly and understand when each is appropriate.
• Particles (は/が/を/に) — these tiny characters determine the grammatical role of every word. Confusing は and が is one of the most common mistakes, and the difference is often contextual rather than rule-based.
• Keigo (敬語) formality levels — Japanese has three layers of politeness: 丁寧語 (polite), 尊敬語 (honorific), and 謙譲語 (humble). Mixing levels in a single sentence is a grammar error that no simple rule can catch.
• No spaces between words — like Chinese, Japanese doesn't use spaces. The checker must first segment text into words before it can analyze anything, and incorrect segmentation cascades into wrong corrections.
• Kanji readings and selection — many kanji share readings. Writing 始める vs 初める (both "hajimeru") depends on context. Homophone kanji errors are the Japanese equivalent of spelling mistakes.
• SOV word order — Japanese follows Subject-Object-Verb order, the opposite of English SVO. Tools trained on English grammar patterns produce false positives when applied to Japanese sentence structure.

Rule-based checkers can catch some of these issues, but AI-powered tools that understand Japanese context and semantics perform significantly better across the board.

Best Japanese Grammar Checkers

1. Enno — Best Free Japanese-Specific Checker

Enno is a free, web-based Japanese proofreading tool built specifically for Japanese text. It catches typos, misused particles, incorrect kanji, and common writing mistakes. Because it was designed for Japanese from the ground up — not adapted from an English tool — it understands Japanese-specific patterns that general tools miss.

• Free to use, no account required
• Catches particle errors, kanji mistakes, and typos
• Japanese-native rule set

Limitation: Web-only. Rule-based, so it misses nuanced grammar and keigo errors. No app integration.

2. Yahoo! Japan 校正 — Solid for Basic Proofreading

Yahoo! Japan's proofreading API powers several Japanese writing tools and offers decent coverage of common errors — misspelled kanji, incorrect particle usage, and punctuation issues. It's available through the Yahoo! Developer Network and is integrated into some Japanese text editors.

• Good coverage of standard Japanese errors
• API-based — integrated into various Japanese tools
• Handles both formal and casual text

Limitation: Requires API integration. Not a standalone tool for most users. Limited grammar depth beyond surface-level checks.

3. FlowWrite — Best for Mac Users Who Write in Japanese

FlowWrite uses large language models to correct Japanese grammar in any Mac application. Select text, press Tab, and it fixes errors in place — including particle confusion, keigo inconsistencies, kanji selection errors, and unnatural phrasing.

• AI-powered — understands Japanese context, particles, and keigo
• Works system-wide on Mac (Mail, Notes, Chrome, Slack, any app)
• Handles kanji, hiragana, and katakana natively
• Also translates between Japanese and English
• Free (20/day) or $2.99/month

Limitation: macOS only. Requires internet connection.

4. ChatGPT / Claude — Best for Detailed Explanations

Pasting Japanese text into ChatGPT or Claude and asking for a grammar review works remarkably well. Both models understand Japanese grammar deeply — including keigo levels, particle nuances, and natural phrasing — and can explain why something is wrong. This makes them ideal for learners studying for JLPT or improving their writing.

• Excellent Japanese grammar understanding
• Can explain particle choices and keigo rules
• Helpful for JLPT preparation
• Free tiers available

Limitation: Copy-paste workflow. No integration with writing apps. Too slow for quick, inline corrections.

5. LanguageTool — Limited Japanese Support

LanguageTool lists Japanese as a community-supported language, but its coverage is minimal. It catches a few spelling errors and basic punctuation issues, but misses most particle errors, keigo problems, and kanji selection mistakes. The rule set is thin compared to its English support.

• Free tier available
• Browser extension and desktop app
• Open source — community can contribute rules

Limitation: Japanese support is shallow. Don't expect it to catch は/が confusion or keigo mixing.

6. Grammarly — No Japanese Support

Grammarly does not support Japanese. If you type Japanese into Grammarly, it either ignores it completely or flags everything as an error. This is worth noting because many people search for "Japanese grammar checker" expecting Grammarly to handle it. It doesn't, and there are no announced plans to add Japanese.

Comparison

For Japanese-English Bilingual Writers

If you write in both Japanese and English — business emails to international teams, bilingual documentation, or switching between languages throughout the day — most grammar checkers force you to choose one language at a time. Switch languages and you need a different tool.

FlowWrite handles this natively. It detects the language of your selected text automatically and corrects accordingly. More usefully, it can translate between Japanese and English in the same workflow: select Japanese text, press Tab, and get a polished English translation (or vice versa). No app switching, no copy-pasting into a translator.

This is particularly useful for bilingual professionals working at global companies, freelance translators, and anyone who regularly moves between Japanese and English. You can draft in Japanese, translate to English, and polish the result — all without leaving your current app.