Japanese Grammar Checker for macOS — Fix Errors Instantly

Writing in Japanese is hard enough without second-guessing every particle. Whether you're a Japanese learner drafting essays, a professional composing business emails in Japanese, or a translator polishing output, grammar mistakes slip through — wrong particles, overly stiff phrasing, unnatural word order. A dedicated Japanese grammar checker built into your writing workflow catches these errors before they reach your reader.

WunderType turns your Mac into a system-wide Japanese grammar checker. Select your Japanese text in any app, press a shortcut, and get corrected text back in place — no browser tabs, no copy-pasting.

How a Japanese Grammar Checker Works in WunderType

WunderType sits in your macOS menu bar and lets you create Custom Prompts — AI-powered text actions with dedicated keyboard shortcuts. For Japanese grammar checking, you create a prompt that instructs the AI to correct grammatical errors, fix particle usage, and make expressions sound more natural, while preserving the original meaning.

This is different from translation. You're not converting English to Japanese — you're taking existing Japanese text and making it grammatically correct and natural-sounding. The AI understands context, so it doesn't just flag errors; it rewrites awkward passages into fluent Japanese.

Before and After

Here's a paragraph with common Japanese grammar issues — incorrect particles, stiff expressions, and redundant phrasing — run through a Japanese grammar checking prompt:

Before

私は昨日、日本語で本を読んだ。とても面白かったです。しかし、文法が少し間違っていたので、修正が必要です。あと、表現が少し硬かったので、もっと自然な言い方に変えたいです。特に、助詞の使い方が問題でした。

Highlight the text, press ⌥⇧⌘J, and WunderType produces:

After

昨日、日本語の本を読みました。とても面白かったです。文法的な誤りや硬い表現を修正し、より自然な言い方に変更しました。特に助詞の使い方も調整しました。

Notice the corrections: 日本語で本 becomes 日本語の本 (correct particle), the redundant 私は is dropped (natural in Japanese), scattered sentences are consolidated into tighter phrasing, and the inconsistent mix of plain and polite forms is unified into polite style (です・ます). These are exactly the kinds of mistakes a Japanese grammar checker should catch.

Setting Up Your Japanese Grammar Checker Prompt

1. Click the WunderType icon in your menu bar and open Custom Prompts.
2. Create a new prompt named Japanese Grammar Checker.
3. In the instruction field, write: "Correct any Japanese grammar errors in the following text. Fix particle usage, tense consistency, and unnatural phrasing. Make the text sound natural and fluent while preserving the original meaning. Do not translate — only correct and improve the Japanese."
4. Assign a shortcut — ⌥⇧⌘J is a good choice for Japanese grammar.
5. Save the prompt.

The key instruction is "do not translate." This tells the AI you're working with existing Japanese text, not asking for a translation from another language.

What It Catches

A well-configured Japanese grammar checker prompt handles the most common mistakes:

• Particle errors — mixing up は/が, に/で/へ, を/が, and other particles that change sentence meaning
• Style inconsistency — mixing plain form (だ/である) and polite form (です/ます) within the same text
• Unnatural phrasing — direct translations from English that sound stiff or awkward in Japanese
• Redundancy — unnecessary subjects, repeated information, and overly long sentences that Japanese typically condenses
• Keigo mistakes — incorrect honorific or humble forms in formal writing

Who This Is For

This prompt is especially useful for Japanese learners writing practice essays or homework, professionals who write emails and documents in Japanese as a second language, and translators who want a quick polish pass on their output. If you already write in Japanese but want a safety net for grammar, this is it.

It's not a replacement for understanding grammar — it's a tool that catches what you miss when you're writing quickly or when you're still building fluency.

Get Started

WunderType is available for macOS 15 and later. Set up a Japanese grammar checker prompt and start correcting Japanese text anywhere on your Mac with a single keystroke.

Download WunderType on the Mac App Store