Grammarly vs QuillBot AI Humanizer

Only one of the two publishes a free allowance in words. QuillBot's Basic mode takes 125 words per input and renews, so a 1,500-word essay is twelve pastes and costs nothing. Grammarly's free plan is counted in AI prompts, 100 a month on the plans page read 9 November 2026, and the humanizer page does not say how many words one prompt covers. The honest comparison is therefore 125 words per input against an unknown; QuillBot wins on the published figure because Grammarly has not published one.

Figures read on the vendors' pages on 9 November 2026. If free volume is the deciding factor, the free humanizer ranking lists a tool that takes 3,000 words per request free.

QuillBot Premium is priced per month, $8.33 billed annually with a $5.00 promotional rate shown on the day read, and the humanizer page states no input limit on Premium, read 9 November 2026. Grammarly's paid plan is priced per month in a currency that depends on the visitor's country, and its allowance is 2,000 AI prompts a member a month, read 9 November 2026. A per 10,000 word price can be computed for neither: QuillBot states no word pool and Grammarly counts prompts. Price is reported here and never scored.

The practical difference is what you are buying. QuillBot Premium bundles the humanizer with a paraphraser, grammar checker and other tools under one plan; Grammarly's plan bundles the humanizer with its grammar, tone and plagiarism features, and the humanizer draws from the same prompt pool as its other generative features.

Grammarly's humanizer page describes the tool as turning AI text into natural writing "while staying true to your original message", lists research, essays, reports and marketing copy as uses, and tells users to "follow the appropriate guidelines for acknowledging AI use", read 9 November 2026. QuillBot's humanizer page describes two rewrite modes, Basic and Advanced, read 9 November 2026. Neither page read for this comparison publishes a detector pass rate, so none is quoted.

The research on the category is about detectors, not about either product. Weber-Wulff and colleagues tested 14 detectors and concluded they were neither accurate nor reliable, with obfuscation worsening performance (Weber-Wulff et al. 2023, International Journal for Educational Integrity, read 9 November 2026). Sadasivan and colleagues found recursive paraphrasing significantly reduced detection rates across detector types on roughly 300-token passages (Sadasivan et al. 2023, arXiv 2303.11156, read 9 November 2026). No detector score should be the only evidence in a misconduct case.

Neither vendor publishes a figure for how much of a passage its humanizer rewrites, so the question cannot be settled from vendor pages. What the pages do show is where each tool puts the control. QuillBot's control is a strength switch, Basic or Advanced, with Advanced held behind Premium after three free uses. Grammarly's control is voice, four presets or a custom voice built from a writing sample, which steers tone rather than how far the text departs from the input.

The run records QuillBot's Basic and Advanced outputs as separate rows and Grammarly's default voice as one row, so readers can see how each control changed the text. The meaning rating treats both tools the same way, by asking whether every claim in the input survives.

The method runs both tools on the same 24 AI-written inputs and 6 human controls, QuillBot in Basic and Advanced and Grammarly on its default voice, and checks every output on GPTZero, Originality.ai, Copyleaks, Pangram and ZeroGPT. Two editors rate meaning kept blind and count errors per 100 words. For QuillBot, free-tier inputs are split to 125 words so the free row is a real free row. For Grammarly the run will record how many prompts the 24 inputs consumed, which gives readers the word-per-prompt figure Grammarly does not publish.