The tool
What the GPT-5 Pro detector does
Paste your text and the GPT-5 Pro detector reads it, then reports the writing patterns common in output from OpenAI's reasoning tier: long, evenly weighted sections, exhaustive coverage of a topic, hedged claims, and structure that reads more like a report than a piece of writing. Each finding comes with the reason it was flagged.
It reports signals in the prose. It does not report who typed it, and it does not report which model was used. Those are two different claims and only the first one is available to anybody.
How it works
How to check text for GPT-5 Pro writing in three steps
One pass, and you get a list of patterns with reasons attached.
- Step 1
- Paste the text. From one sentence up to 12,000 characters per check, which is more than most free checkers allow.
- Step 2
- Run the check. The text goes to our server, a model reads it, and the findings come back.
- Step 3
- Read each flag. It names a pattern and says what makes it recognisable, so you can decide whether to rewrite or leave it.
Background
What GPT-5 Pro is, and how it differs from GPT-5
GPT-5 Pro is the high-compute tier of OpenAI's GPT-5 family, above the standard model and above Thinking mode. Published explainers describe it running several reasoning threads in parallel rather than one linear pass, reaching an answer more slowly and more accurately, and fanning out searches or tool calls to assemble a long synthesised answer.
The important part for anyone checking text: the difference is in how it reasons, not in how it writes. None of the explainers describes a distinct Pro prose style, and that absence is meaningful. What changes in practice is scale and shape, longer answers, heavier structure, more thorough coverage, while the sentence-level habits are the ones GPT-5 already had.
The patterns
What GPT-5 Pro output tends to look like
These are the patterns a check reads. Every one of them is also something a careful human writer does sometimes, which is why the output is a list and not a verdict.
- Completeness
- Every angle covered, including the ones nobody asked about. Human writers leave things out because they ran out of room or interest.
- Heavy structure
- Headed sections, nested lists, a summary at the top and another at the bottom. Report shape applied to something that was not a report.
- Even weighting
- Each section given roughly the same length, whether or not it deserved it.
- Hedged claims
- A qualifier in front of statements that were not in doubt.
- Flat rhythm
- Sentence lengths clustering in the same range throughout.
- The em dash
- Still a frequent tell across GPT-5 output. The em dash remover strips them separately if that is all you want gone.
Straight answer
Can a detector tell GPT-5 Pro from GPT-5?
No, and this tool does not try. The whole idea of a tier-specific detector assumes the tier leaves a signature in the prose, and nothing published supports that. The explainers say the tier changes reasoning depth and error rate. Detection research reports that classifiers trained on one model's output transfer badly to another's, which is the opposite of what tier identification would need.
The model behind this check is also given an explicit instruction never to claim which system produced a text. So what you get is a description of the writing. If you know a Pro-tier model was involved, the findings will usually match what you expected. That is corroboration, not identification.
The missing number
Why there is no GPT-5 Pro percentage score
Other checkers publish figures: 97 per cent detection, under 3 per cent false positives, 99 per cent accuracy. Each is measured by the vendor on the vendor's own sample set, and none of them can be checked by the person reading the page.
We have run no such measurement, so there is no number here. What you get instead is a flag attached to a specific sentence with a stated reason, which is the version you can actually argue with. If a reason does not describe your writing, the flag is wrong and you can see that it is wrong.
Being wrongly flagged
Why human writing gets flagged as GPT-5 Pro
There is a risky profile and it is worth knowing. Short samples are riskier than long ones, because there is less to read. General writing is riskier than specific writing. Essay-shaped writing, introduction, three body sections, conclusion, is riskier than anything with an unusual structure. A detector that publishes its own false-positive guidance says the same thing.
On top of that, the whole thorough-and-well-organised profile is what a good technical writer produces on purpose, and what many people writing English as a second or third language produce because a level register is the one they trust. A flag describes prose. It is never a finding about a person.
Who it is for
Who uses the GPT-5 Pro detector, and when
Writers who used a reasoning model for a long research answer and want to know which parts still read as generated. Editors handling a submission that covers everything and commits to nothing. Students checking work before a portal does. Teams reviewing a batch of long-form drafts where the length itself is the tell.
Five checks per rolling 24 hours, 12,000 characters each, no account. That suits careful passes on pieces that matter rather than a pipeline, which is what this tool is for.