Japanese AI detector

GPTCleanup Pro's Japanese AI detector reads a passage of Japanese text and reports the patterns typical of AI-generated Japanese writing: register consistency between desu-masu and da-dearu, full-width punctuation, and stock closing lines like いかがでしたか, with each signal named rather than folded into one number. It answers the question people actually search, is this Japanese text AI-written, with a breakdown rather than a verdict.

It is a server tool by necessity: the pattern model is too large to run in a browser, so text is sent to our AI server to be scored and the result returned to the page. You get 5 free checks in any rolling 24 hours, no account required.

Japanese carries tells that a detector built around English phrasing would never register. No single item below is disqualifying; the read is a function of how many co-occur in one sample.

The いかがでしたか closing

いかがでしたでしょうか wrapping up a piece that never needed the question, a template so common in AI-generated Japanese blog content that it carries its own reputation among readers.

A register that never slips

です・ます kept polite throughout, or だ・である kept plain throughout, without the accidental mid-paragraph switching genuine drafts tend to have.

Suspiciously clean full-width punctuation

、。！？ rendered perfectly full-width throughout, without the stray half-width ASCII marks ordinary typing sessions tend to introduce.

No word spacing, plus odd exceptions

Japanese carries no spaces between words. A stray space inserted around an English loanword or after a punctuation mark stands out precisely because the rest of the text has none.

A closing summary paragraph

A tidy wrap-up appended to a piece that never called for one, functioning as いかがでしたか does even when that exact phrase is avoided.

One round trip to the server, then a reasoned result.

Step 1

Paste the Japanese sample. A longer passage gives the model more structure to weigh.

Step 2

Run the check. The text is sent once to our AI server, scored against the patterns above, and nothing further is done with it.

Step 3

Review each flagged pattern and its stated reasoning. The output is an argument you can inspect, not a number you're asked to trust.

Not with confidence. Most models default to a polite, consistent desu-masu register in Japanese regardless of which one produced the text, and several share the same いかがでしたか-style closing habit, so these signals point toward machine-written Japanese broadly rather than any single model.

A prompt requesting a plain, literary da-dearu register, or a casual tone, erodes most of this signal in one step. A strong match is grounds for a closer look, not a determination of authorship.

Japanese has solid training data overall, but the writing that reads most like this detector's default profile is exactly the writing with nothing to do with AI.

Keigo-heavy business writing

Formal honorific Japanese in business correspondence already keeps a rigidly consistent polite register, for reasons that predate AI by decades.

Machine-translated Japanese

Japanese translated from English by a separate tool commonly lands as grammatically correct but stiff, matching this detector's default profile.

Rule-following non-native writers

Desu-masu consistency is standard Japanese-course material as the safe default, so a learner following instruction closely produces the same shape a model defaults to.

A flag from this tool is a signal, not a finding, and formally consistent Japanese overlaps with this detector's default profile more than casual writing does.

Preserve your drafts

Earlier versions are the clearest evidence a piece was composed, not generated whole.

Document your intended register

Why you kept desu-masu or da-dearu strictly consistent, for a business or academic context, is context a generic default cannot supply.

Request the named signal

A specific pattern, a closing phrase or a register choice, can be examined on its own terms. An unexplained score cannot.

Editorial teams screening Japanese submissions, instructors weighing a second opinion on unusually polished essays, and writers reviewing their own drafts before submission.

5 free checks per rolling 24-hour window, tracked without an account. The window reopens continuously rather than resetting at a fixed hour, which covers ordinary use, one submission, one paragraph under review, without friction.