Compare · GPTZero

GPTZero alternatives

GPTZero is the detector most students and educators can name. This page states what it does well, what a style guess can and cannot tell a writer, and what an alternative looks like when the detection has to explain itself.

What GPTZero is

GPTZero is an AI detector. It flags text it judges likely to be machine-written, highlights the sentences behind the verdict, and cites sources for its claims. It is built for educators, recruiters, and students.

Pricing as of 11 August 2026: Premium at $12.99 for 300,000 words, Professional at $24.99, and API access from $45 a month. A free tier allows a limited number of checks.

Where GPTZero excels

The sentence-level highlight is a step past a single verdict. A reader can see which lines the classifier doubts instead of one number for the whole page.

The education focus is organized: LMS integrations, class management, and materials written for teachers.

For a school that wants one vendor and one dashboard, GPTZero is the incumbent for a reason.

The limit that matters

GPTZero is a statistical classifier. It guesses authorship from style, and the guess comes back as a score with no account of which patterns it weighed.

Classifiers flag honest writing. The documented record includes non-native speakers flagged at higher rates and students who had to prove they wrote their own work. That is a category problem, and GPTZero is in the category.

GPTZero checks and reports, and its writing feedback stays at suggestions — there is no rewrite engine in the product. A flagged draft leaves with a verdict; the work of fixing it happens elsewhere.

The alternative angle: tells you can read

underslop detects differently on purpose. Instead of a style guess, it reports the specific AI tells in a draft, names each pattern, and marks the ones that survive the rewrite.

A tell is readable: an unattributed claim of proof, an em-dash chain, a rule-of-three list. You can agree or disagree with a named pattern. You cannot argue with a black box.

The rewrite is provenance-preserving. It changes the writing, not the record, and residual tells stay marked. Every run logs what changed and why, so a disputed flag has a paper trail.

Price: $0.10 per 1,000 words, with a free tier at 500 words per run. GPTZero banks 300,000 words at $12.99; underslop sells edits, not checks, so the units do not compare directly.

The verdict

For a school that needs a detector with a dashboard and a vendor to call, GPTZero is the easy choice.

For a writer who was just flagged, a verdict without an explanation and without a fix is a dead end. The alternatives below exist for that second reader, and underslop is the one that starts from the draft instead of the verdict.