GPT-4.5 detector

GPTCleanup Pro's GPT-4.5 detector reads a block of text and reports the patterns associated with GPT-4.5's writing, the OpenAI research-preview model that predates the GPT-5 line, with each signal named and explained rather than compressed into one score that hides its own reasoning.

It's 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 is returned to the page. You get 5 free checks in any rolling 24 hours.

State this plainly rather than implying otherwise: the detector cannot establish that GPT-4.5 specifically, rather than a different OpenAI model, produced a given passage. It reports patterns associated with GPT-4.5's default voice, offered as signals worth a closer look.

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

Step 1

Paste the sample. A longer passage gives the pattern model more structure to weigh; a single sentence rarely produces a confident read.

Step 2

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

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.

OpenAI described GPT-4.5 on release as writing more naturally and with a warmer, more emotionally attuned register than the models preceding it, a direction distinct from the leaner, answer-first style the GPT-5 line later adopted. No single item below is disqualifying alone; the read is a function of how many co-occur across a passage.

Warmer, more conversational register

A softer, more personable tone than the terser style associated with GPT-5-era output.

More descriptive, figurative language

A greater willingness to reach for a metaphor or a scene-setting detail rather than stating a fact and moving on.

Fuller paragraph development

Ideas built out across several sentences rather than delivered in a single terse line.

Fewer forced tricolons

Reduced reliance on the three-item rhythm common in the ChatGPT models before it.

Rounder closing sentences

A closing line that wraps up the point gently, rather than the flatter endings typical of leaner later models.

Not with confidence, and stating that plainly is more useful than avoiding the question. GPT-4.5's warmer style and GPT-5's leaner one describe general directions the models were tuned toward, not a fixed line every response sits on. A GPT-4.5 answer to a terse system prompt can read leaner than a GPT-5 answer to a chatty one.

A system prompt further erodes the signal, since instructing any model to write in a specific register erases most of its default profile in one step. What this detector reports is a match to patterns typical of GPT-4.5's default voice, not a determination of which specific model, or person, produced the text under review.

This is why a single, version-agnostic score would be a weaker product than what's offered here. A detector tuned to GPT-4.5's warmer habits and pointed at GPT-5's leaner output is extrapolating outside its evidence, so this site runs a separate checker per model rather than one number claiming to cover all of them.

Several categories of legitimate human writing share these patterns for reasons unrelated to any model, and a serious detector should say so.

Warm, personable writers

A naturally conversational, emotionally attuned style predates GPT-4.5 by decades and shares real surface features with it.

Descriptive nonfiction and essays

Figurative language and scene-setting detail are standard craft choices in these genres, independent of any model.

Fuller, older-style paragraphing

Writers trained under older style conventions favouring developed paragraphs read closer to GPT-4.5's habits for institutional reasons.

Second-language writers

Rounder, more explanatory sentence construction is common instruction in many ESL courses.

A flag from this tool, or from any detector, is a signal rather than a finding.

Preserve your drafts

Outlines and marked-up revisions are the clearest evidence a piece was composed, not generated whole.

Retain version history

Most editors log revisions automatically. Leave it intact while any question is open.

Be prepared to discuss specific choices

Explaining why a line or structure exists is materially harder to fabricate than the prose itself.

Ask for the named signal, not the label

A specific pattern can be examined on its own terms. An unexplained score cannot.

The same checker, applied at different points in a review process.

Editorial and publishing teams

Reviewing older submissions against the writing habits of a model in wide use before GPT-5 became the default.

Instructors

One input among several when a submission reads unusually polished, never the sole basis for a decision.

Writers reviewing their own drafts

Checking whether their own habits read as machine-typical before submission.

Researchers

Comparing writing associated with an earlier model generation against newer output for a specific project.