Free GPT-5 detector & checker

The tool

What the GPT-5 detector does

Paste your text and the GPT-5 detector reads it, then reports the writing patterns that turn up in GPT-5 output: the even sentence lengths, the hedge before every firm statement, the three-item list used as a default shape, the closing paragraph that summarises instead of finishing. Each finding comes back with the reason it was flagged.

It reports signals. It does not report proof. Nothing in the text records who typed it, so what you get is an informed read of the writing, and the decision about what to change is still yours.

How it works

How to check text for GPT-5 writing in three steps

One pass and you have a marked-up view of your own draft.

Step 1

Paste the text. Anything from a single sentence up to 12,000 characters goes in at once.

Step 2

Run the check. The text is sent to our server, an AI model reads it, and the findings come back.

Step 3

Read the flags. Each one names a pattern and says what makes it recognisable, so you can rewrite that sentence or leave it alone.

The model

What changed in GPT-5's writing, and what did not

GPT-5 writes looser than GPT-4 did. Published side-by-side comparisons describe a more informal register, shorter openings and fewer of the stiff formal constructions that made earlier ChatGPT output easy to spot by eye. That makes eyeballing a draft less reliable than it used to be.

The habits underneath moved less than the surface. Testing published by Originality.ai on GPT-5 rewrites found em dashes in most of the machine-written set and none in the human control set, and found GPT-5 tracking the readability of whatever it was given more closely than earlier models did. A model that matches its source is harder to catch on tone alone and easier to catch on habit.

Punctuation habit

The em dash survived the version bump. If you want them gone, the em dash remover strips them in one pass without touching anything else.

Even rhythm

Human paragraphs run long, then short, then long. GPT-5 paragraphs tend to land in the same range each time.

Hedged claims

Statements arrive wrapped: it is worth noting, it is important to remember, in many cases.

Symmetrical structure

Three points, three examples, a matched sentence for each. Real arguments are lopsided, because some points need more room than others.

Straight answer

Can a detector tell GPT-5 from GPT-4 or Gemini?

Not reliably, and this tool does not claim to. The model behind the check is given explicit instructions never to assert who or what wrote a piece of text, and to describe observable signals instead. Tools whose product name promises model attribution are promising something no one has demonstrated.

What is true is that the patterns this page describes are common in GPT-5 output, so if you drafted with GPT-5 the findings will usually line up with what you already know. That is a useful editing signal. It is not an identification.

The missing number

Why there is no GPT-5 percentage score

Most free detectors hand back a figure: 94 per cent AI, 6 per cent human. Competitors also publish their own accuracy claims, 96 or 99 per cent, measured on their own sample sets. Both numbers look like measurements and neither can be checked by the person reading them.

This checker returns findings instead. A flag on a specific sentence with a stated reason is something you can agree with, argue against, or act on. A percentage is not. If you want a number, other tools will give you one, and the question worth asking them is what it was measured against.

Being wrongly flagged

Why clean human writing gets flagged as GPT-5

The signals a checker reads are signals of tidy, evenly-weighted prose. Careful writers produce that on purpose. So do people writing in English as a second or third language, who often hold to a safe, level register because it is the one they trust. So do technical writers working to a house style, and anyone who has been edited hard.

That is not a bug you can engineer away, because the evidence genuinely is ambiguous: the text looks the way it looks whoever produced it. It is a reason to treat any flag as a prompt to look closer, and never as a finding about a person.

Limits

Length limits and free GPT-5 detector checks

Each check takes between 1 and 12,000 characters, which is roughly 1,800 to 2,000 words of prose. Longer pieces get split at a section break and checked in parts. Keep the opening and closing paragraphs together in one of those parts, since structural patterns cluster at both ends.

There are 5 free checks per rolling 24 hours, counted per browser, with no account and no sign-up. The limit exists because every check is a real model call on our server. It is not a trial that expires: the window rolls, so the checks come back.

Who it is for

Who uses the GPT-5 detector, and when

Writers who drafted with GPT-5 and want to know which parts still sound drafted. Students checking coursework before a submission portal sees it. Editors reading a submission that feels oddly smooth. Marketers checking copy before it goes live, because the tells that a checker picks up are the same ones a reader half-notices.

The common thread is that all of them want to know which sentences to rewrite. That is what a list of flagged patterns gives you, and it is why the output is a list of patterns rather than a verdict.