What an AI detection score actually means

An AI detection score answers one narrow question: how strongly does this text resemble patterns the model associates with AI writing? It does not record who sat at the keyboard, and it does not replace a reading of the essay.

The percentage is not a share of stolen sentences

A result of 40% does not mean 40 sentences were generated and 60 were typed by hand. It means the model’s overall reading of the document landed in a middle band. The highlights are a separate layer. They show which passages contributed to that reading.

Three figures get mixed up:

• The overall score is the document-level signal.
• The highlights are the passages the report asks you to inspect.
• The confidence note, when the report shows one, tells you how stable that reading is on this text.

A highlight on 30 words inside a 100-word paragraph is not proof that those 30 words were generated. It is a pointer. Read them in place.

How Certaffy bands a result

Use the band, then the passages.

• 0–29% — low AI signal. Keep your normal review. Do not file the essay as “certified human.”
• 30–74% — review required. Read every highlight, compare the draft if you have one, and check citations before you comment on authorship.
• 75% or higher — elevated AI signal. The report is showing a strong pattern. Talk with the writer and look at earlier versions before you decide anything.

Short text, a scanned PDF with bad extraction, and a page that is mostly quotations will make any of these bands less informative. If the extracted text does not match the document, ignore the score and fix the file first.

Two different mistakes

A false positive flags human writing. Polished, formal, or heavily edited prose can do this. A miss leaves AI writing unmarked, especially after someone rewrites it by hand. A tool can look “careful” by flagging less, and then miss more. That is why the highlights matter as much as the headline number: you can see what the model used.

The false-positive guide is the page to use when a result might affect a student. For a worked reading of mixed pages, see how highlights work on mixed writing.

A score is the start of the file, not the end

Put the report next to the draft, the sources, and the writer’s explanation. If those agree with the highlights, you have a review. If they do not, you have a reason to slow down. Either way, the percentage was never the decision.

Try a text on the free AI detector. Full highlighted reports, PDF downloads, and draft comparison are on Academic Pro.