You mostly need to check, not fix
1,200 words per free check with no limit on how many checks you run is a real, generous free tier for detection on its own.
The short answer
Choose Scribbr if you mainly need to check a document-length draft and don't mind a separate step for rewriting. Choose Penlify if you want the sentence that got flagged to become a rewrite candidate in the same place, without dropping to a 125-word box.
You want the fix in the same place
Rewriting a flagged sentence doesn't mean leaving the detector for a separate 125-word tool — it happens in the same free workspace.
Feature comparison
Limits below are read directly from Scribbr's AI Detector and AI Humanizer pages, not estimated. Scribbr does not display a premium pricing tier on either tool's page.
| Area | Penlify | Scribbr |
|---|---|---|
| Free detection limit | ~6,000 characters per check (about 1,000 words), 3 checks/month. | Up to 1,200 words per check, unlimited checks. |
| Free rewriting limit | Same length range as detection, 5 rewrites/month. | Separate AI Humanizer tool, 125 words per submission. |
| Detection and rewriting | One workspace — rewrite a flagged sentence without switching tools. | Two separate tools/pages, not a scoped flag-to-rewrite step. |
| Sentence-level view | Yes — each sentence scored separately. | Distinguishes human, AI-generated, and AI-refined writing; not confirmed as a per-sentence rewrite queue. |
| Other bundled tools | None — detection and rewriting only. | Plagiarism checker, citation generator, paraphraser, summarizer, grammar checker, human proofreading service. |
| Built for | A writer checking and fixing their own draft. | Students and academics needing a broader research-writing toolkit. |
Honest tradeoff: Scribbr's detector free tier is not the weak point here — 1,200 words with no check limit is genuinely competitive. The gap is the fix: humanizing is a separate, much smaller-capacity tool. Penlify keeps detection and rewriting at the same scale, in the same place.
Limits checked directly against Scribbr's AI Detector page and AI Humanizer page on 29 August 2026. No pricing tier was visible on either page at the time of review; limits and offerings can change.
A generous detector, a narrow fix
Scribbr's AI Detector page states it plainly: unlimited free checks, up to 1,200 words each. For a lot of real drafts — an essay section, a cover letter, a few paragraphs of a paper — that's enough room to check the whole thing in one pass, no account required.
The AI Humanizer is where the story changes. It's a separate tool on a separate page, and its input box shows a 125-word cap per submission — short enough that a flagged paragraph often won't fit in one go. There's no premium tier advertised on either page to raise that limit, so as tested, fixing anything beyond a sentence or two means running it through in pieces.
Penlify keeps detection and rewriting at roughly the same scale on purpose — both operate up to about 6,000 characters on the free plan, in the same workspace, so a flagged sentence doesn't drop into a much smaller box to get fixed.
Common questions
Is Scribbr's AI detector free?
Yes. Scribbr's own AI Detector page states it allows an unlimited number of free checks, with a limit of up to 1,200 words per submission. That's a genuinely generous free detector, comparable to or larger than Penlify's per-check limit.
Can Scribbr rewrite AI-flagged text for free?
Scribbr offers a separate AI Humanizer tool, and its input field shows a 125-word limit per submission — roughly one short paragraph. Penlify's free rewrite step handles the same length range as its free detection check, without a separate, much smaller cap for the fix step.
Are Scribbr's AI Detector and AI Humanizer the same tool?
No, they're separate pages and separate tools on Scribbr's site. Penlify's detection and rewriting happen in one workspace, so a flagged sentence can be rewritten without switching tools.
Test the workflow with your own draft
Start with the private analyzer. It gives value without requiring an account or sending the text to Penlify.