Grammarly AI Humanizer vs Undetectable AI

Grammarly. Its product page tool is free with basic humanization and a free account adds the Humanizer agent with four preset voices and six languages, read 9 November 2026. The free account's 100 AI prompts a month renew, so a user who rewrites a paragraph a day has a standing allowance rather than a countdown. Whether one humanizer run costs one prompt, and whether the no-account tool on the product page draws on the 100 at all, is not stated on either Grammarly page read.

Undetectable AI's free use is a trial: 250 words in total, after which further use needs a paid plan, read 9 November 2026. That is one long paragraph, once.

Grammarly figures read 9 November 2026; Undetectable AI trial checked 8 November 2026. The limit on Grammarly's side is informational: the vendor publishes neither a word cap nor how prompts map to words, so a heavy user cannot plan a month from the page. The limit on Undetectable AI's side is arithmetical and exact.

Undetectable AI. Its pricing page prices words on a slider: 10,000 a month at $9.99 or $5.00 a month on the yearly toggle, 20,000 at $19.00 or $9.50, 35,000 at $31.00 or $15.75, read 9 November 2026, with the yearly rate charged as one payment, $60.00 for the entry tier. A buyer knows the pool, the price and the charge before paying. What the page does not print is a per-request cap, so a long document is limited by the month and not by the paste.

Grammarly's Pro card shows $12 without stating whether that is monthly or yearly billing, and its plans page counts generative use in AI prompts, 2,000 a member a month on Pro, read 9 November 2026. The price buys the whole suite: grammar, tone, citations, an AI detector and an authorship record alongside the humanizer. For a reader who wants the humanizer alone, no part of the $12 can be attributed to it. Price is reported on this site and never scored.

The two vendors state opposite aims. Grammarly's product page says the humanizer "is not intended to bypass AI detectors", describes its job as making AI text read naturally while keeping the meaning, and asks users to acknowledge AI assistance in academic or professional work, read 9 November 2026. Undetectable AI's pricing page lists "Passes AI detectors" on every plan and offers to refund the cost of a humanization if the output is flagged as not human, read 9 November 2026.

Both read 9 November 2026. On this site the aim matters less than the result, and the result is unknown until a run exists. Weber-Wulff and colleagues tested 14 AI text detectors and found every one below 80 percent accuracy, with accuracy falling further on paraphrased and machine-translated text (Weber-Wulff et al. 2023, International Journal for Educational Integrity, read 9 November 2026). A light rewrite of the kind Grammarly describes is a paraphrase, so detector readings may move whether or not the vendor aims at them, and a heavy rewrite of the kind Undetectable AI sells may move readings at a cost to meaning that no pricing page measures.

The published method weights meaning kept at 35 points of 100, errors added at 20, detector pass rate at 30 and limits and access at 15, with five named detectors and two editors rating every output blind. When a run is published, this page gains meaning, error and per-detector fields for both tools. No detector score should be the only evidence in a misconduct case. Anyone writing for a class should check their institution's AI policy before using either tool; a humanizer does not make undisclosed AI use acceptable.