QuillBot vs Undetectable AI: Honest 2026 Comparison

These two get compared because both have a button labelled "Humanize", and that is where the resemblance ends. QuillBot is a writing suite that has been paraphrasing student essays since before large language models existed and added a humanizer because customers asked. Undetectable AI is a humanizer first, built and marketed around one promise: text that passes AI detectors, with a refund if it does not.

I read both vendors' own pages on 14 September 2026, checked what the free tiers actually allow, and wrote down which one a student, a working writer or a content team should pay for. One note before the prices: I do not think using either tool to pass off machine writing as your own in a graded or contractual setting is a good idea, and neither vendor's guarantee changes that. What follows is about the tools.

QuillBot vs Undetectable AI at a glance

The core difference

QuillBot is a general-purpose writing assistant. The paraphraser is the heart of it, with Standard and Fluency modes free and nine modes plus unlimited custom modes on Premium; around it sit a grammar checker, a summariser, a citation generator, a translator, an AI detector and a humanizer. Its free plan has real limits (125 words per paraphrase, six humanizer uses a day) but it is a plan, not a trial, and millions of students live on it.

Undetectable AI is a specialist. You paste AI-written text, choose a readability and purpose, and it rewrites the text to read as human and to pass the detectors it lists on its page, with a refund on the humanization cost if the output is flagged. It bundles its own detector so you can check before and after, sells words per month, and has an API for teams who do this at volume. There is no grammar checker, no summariser, no citations; there is one job.

"QuillBot sells you a better draft. Undetectable AI sells you a draft that a detector will not flag. Those are different products with different customers, and pretending otherwise is how people buy the wrong one."

QuillBot: the writing-suite play

QuillBot's premium page on 14 September 2026 listed the free plan at $0 with paraphrasing up to 125 words in two modes, basic grammar fixes, humanizing up to 125 words six times a day, basic summaries and limited detector access; and Premium with full paraphrasing in unlimited modes, advanced grammar recommendations, full humanizer and detector access and plagiarism prevention. QuillBot's own pricing FAQ page states the Premium ladder in US dollars: $8.33 a month on the annual plan ($99.95 billed every twelve months), $13.31 a month on the quarterly plan ($39.95 every three months), and $19.95 on the monthly plan. A Team plan adds usage metrics, user management and centralised billing, priced per seat. Note that QuillBot shows regional prices by location; the page we opened displayed rupees, so check the figure in your own currency.

Where QuillBot earns its keep is daily writing: rephrasing a clumsy paragraph, tightening an email, checking grammar in a second language, summarising a paper. The humanizer is a bonus, and for most of its users the honest advice is to use the paraphraser and rewrite the result yourself.

Undetectable AI: the specialist play

Undetectable AI's pricing page on 14 September 2026 listed four word-based tiers, each with a monthly and a heavily discounted annual price: 10,000 words a month at $9.99 monthly or $5 a month charged annually ($60 a year); 20,000 words at $19 or $9.50 ($114 a year); 35,000 words at $31 or $15.75 ($189 a year); and 50,000 words at $42.50 or $21.25, with custom plans above that. Every tier lists the same features: passing AI detectors, writing-level matching, watermark-proof output, API compatibility, an unlimited "Human Auto Typer" and unlimited AI detecting. A free trial is offered, and the page carries a money-back guarantee: if anything it produces is flagged as not human, it refunds the cost of humanization.

Where Undetectable AI earns its keep is volume: a content team that drafts with AI and needs every piece to read as human before it ships, and would rather pay per word than per seat.

Pricing, honestly

QuillBot's figures come from its own pricing FAQ page in US dollars and its premium page for plan contents; Undetectable AI's from its pricing page. All read on 14 September 2026.

On annual billing they are within a few dollars of each other. The difference is what you get: QuillBot's $8.33 buys a whole writing suite with unlimited paraphrasing; Undetectable AI's $5 buys 10,000 humanized words. A writer gets far more from the first; a team humanizing 40,000 words a month is better served, and better guaranteed, by the second.

Which one should you pick?

• You write and edit every day and want one tool → QuillBot Premium.
• You are a student who needs paraphrasing and grammar on a budget → QuillBot's free plan, then Premium annual.
• Your only task is making AI drafts read as human at volume → Undetectable AI, sized by words.
• You want a guarantee on passing detectors → Undetectable AI is the only one of the two that offers one.
• You need citations, summaries or translation → QuillBot; Undetectable AI does not do them.
• You are unsure → QuillBot's free plan and Undetectable AI's trial cost nothing; run the same 500-word draft through both.

Frequently Asked Questions

Is QuillBot or Undetectable AI better at humanizing?

Undetectable AI, on its own terms: it is built for the task, tests against its own detector, and refunds the humanization cost if output is flagged. QuillBot's humanizer is a feature within a writing suite and makes no such promise. For light, occasional use QuillBot is fine; for volume or a guarantee, Undetectable AI.

Does QuillBot have a free plan?

Yes. Its premium page lists a free plan with paraphrasing up to 125 words in two modes, basic grammar, humanizing up to 125 words six times a day, basic summaries and limited detector access. Undetectable AI offers a free trial rather than a free plan.

How much is QuillBot Premium?

QuillBot's own pricing FAQ states $8.33 a month on the annual plan ($99.95 billed every twelve months), $13.31 a month quarterly ($39.95 every three months) and $19.95 monthly, as read on 14 September 2026. Prices are shown regionally, so your local figure may differ.

How much does Undetectable AI cost?

On 14 September 2026 its pricing page listed 10,000 words a month at $5 billed annually or $9.99 monthly, 20,000 at $9.50 or $19, 35,000 at $15.75 or $31, and 50,000 at $21.25 or $42.50, with custom plans above that.

Can either guarantee my text will pass an AI detector?

Undetectable AI offers a refund of the humanization cost if its output is flagged as not human. QuillBot offers no such guarantee. No tool can guarantee a result against every detector, and using either to misrepresent authorship where it matters is a bad idea regardless.

Which is better for students?

QuillBot, and by a wide margin, because paraphrasing, grammar, summaries and citations are the daily work of studying and its free plan covers the basics. Undetectable AI has no place in that workflow beyond the one task, and that task is one most institutions prohibit.

Final verdict

QuillBot is a writing tool with a humanizer in it. Undetectable AI is a humanizer with a guarantee on it. Priced on annual plans they cost about the same, and the right choice depends entirely on whether humanizing is one of your tasks or the only one.

For writers and students, QuillBot. For content teams humanizing at volume who want a refund if it fails, Undetectable AI.

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Article by Sohail Akhtar, Founder of TheToolsVerse. Prices read from quillbot.com's premium page and pricing FAQ and from undetectable.ai/pricing on 14 September 2026.

Neither QuillBot nor Undetectable AI paid for this comparison. Some links are affiliate links. How paid placements work.