Free GPT-4.5 detector & checker

GPT-4.5 detector

What the GPT-4.5 detector does

This GPT-4.5 detector checks a paragraph, an essay or an email against the writing habits associated with GPT-4.5, the OpenAI research-preview model released before the GPT-5 line. It answers with a plain-language list of what it found and why, not a single confidence score standing in for an answer nobody can actually give.

This is a server tool, not a browser script. Your text is sent to our AI server to be scored, and you get 5 free checks in any rolling 24 hours. There's no account to create.

One thing to be upfront about: it cannot tell you whether text was written by GPT-4.5 specifically as opposed to a different OpenAI model. What it reports are patterns associated with GPT-4.5's writing, described as signals worth a closer look, not a settled answer about origin.

How it works

How to run the GPT-4.5 detector on your text in three steps

Paste, run, read. Nothing to configure first.

Step 1

Paste the text you want checked. A paragraph is enough to run; a longer sample gives the check more to work with.

Step 2

Press Check text. It goes to our AI server once, gets scored, and the result comes back to the page.

Step 3

Read each flagged signal and the reason behind it, then judge for yourself what it's actually worth.

GPT-4.5's writing patterns

How GPT-4.5's writing tends to differ

GPT-4.5 was described by OpenAI on release as writing more naturally and with a warmer, more emotionally attuned register than the models before it, a noticeably different direction from the leaner, answer-first style the later GPT-5 line moved toward. That contrast is what a GPT-4.5 checker is actually reading for.

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 plainly and moving on.

Fuller paragraph development

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

Fewer forced tricolons

Less reliance on the three-item rhythm that showed up heavily in the ChatGPT models before it.

Rounder closing sentences

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

Straight answer

Can you tell GPT-4.5 apart from GPT-5 by the writing alone?

Not with certainty, and it's worth saying plainly. GPT-4.5's warmer style and GPT-5's leaner one describe general directions, not a fixed line every response sits on. A GPT-4.5 answer written to a terse system prompt can read leaner than a GPT-5 answer written to a chatty one.

A system prompt changes almost everything about a model's default voice. Tell a model to write in a specific register, and most of its typical profile disappears. This tool reports patterns typical of GPT-4.5's default voice, not a claim about which specific OpenAI model, or which person, wrote a given piece of text. Treat a match as a lead worth a closer look, never as an answer on its own.

Why flags happen

Why false positives happen

Warm, descriptive, fuller-bodied prose is also just a writing style plenty of people use on purpose, for reasons that have nothing to do with any model. A blog post written in a friendly, expansive voice will share real surface features with GPT-4.5's output.

Writers who favour a warmer register, or who were trained on older style guides that valued fuller paragraph development, get flagged more than they should. A flag here says something about a style, not about who actually wrote the piece.

If you're flagged

What to do if you're accused of using GPT-4.5

A flag is a signal, not a verdict, and no one should treat it as one on its own.

Keep your drafts

Earlier versions and notes are the plainest evidence a piece grew, rather than appearing whole.

Keep version history on

Most editors log revisions automatically. Don't clear it while a question is open.

Be ready to talk through the work

Someone who wrote a piece can usually explain a specific choice in it. That's harder to fake than the prose itself.

Ask what the flag actually found

A named signal can be discussed on its merits. A bare score can't.

Who uses it

Who uses the GPT-4.5 detector, and when

Same tool, several different reasons to open it.

Editors reviewing older submissions

Checking a piece against the writing habits of a model that was in wide use before GPT-5 replaced it as the default.

Teachers

Getting a second opinion on writing that reads unusually polished, as one input among several, not a grading tool.

Writers checking their own work

Running a draft through to see whether their own habits are reading as machine-typical.

Researchers

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