Related
- HumanFlow vs Undetectable.ai — where we sit against the first of these, including where it beats us.
- HumanFlow vs StealthWriter — and against the second.
- Every humanizer we track, ranked — on published limits rather than on claims.
Undetectable.ai vs StealthWriter
HumanFlow is not one of the two tools on this page. We make a competing product, so weigh this accordingly — our methodology sets out how we source competitor figures and what we refuse to claim.
Their free tiers are opposite philosophies — 250 words once, against ten rewrites a day that keep coming.
Last reviewed 15 August 2026 · The HumanFlow team
Why people compare these two
These are two of the most visited tools in the category, so they turn up together in almost every roundup and in most people's shortlists. They are also priced far apart — Undetectable.ai's annual rate is a third of StealthWriter's — which makes the comparison look settled before anyone reads the allowances.
It is not settled, because the two companies have made genuinely different bets about what a trial is for.
Side by side
| Feature | Undetectable.ai | StealthWriter |
|---|---|---|
| Entry price, monthly | $9.99 | $20 |
| Entry price, billed yearly | $5 | $16.67 |
| Included at entry | 10,000 words / month | 50 humanizations a day |
| Per-request cap | No stated per-request cap | 5,000 words |
| Free tier | 250-word trial | 10 humanizations a day and 10 AI scans a day |
| Free per request | 250 words | 1,000 words |
Undetectable.ai figures read from their pricing page on 15 August 2026; StealthWriter from theirs on 4 August 2026.
What actually separates them
Undetectable.ai gives 250 words, once. That is a paragraph, it does not renew, and every tool in this category handles a paragraph well — the seams in machine writing appear over pages, not sentences. What the trial demonstrates is that the service is online.
StealthWriter gives 10 humanizations a day at up to 1,000 words each, ongoing. That is the largest free allowance in this set and it is enough to run real documents through repeatedly before paying anything.
The paid tiers invert the impression. Undetectable.ai is $5 a month billed annually for 10,000 words; StealthWriter is $16.67 a month billed annually and meters in humanizations a day rather than words a month. So the cheaper tool asks you to commit on less information, and the dearer one lets you find out first.
Which to pick
Pick Undetectable.ai if the annual price is the deciding factor and you already know the output suits you. Nothing in this pair beats $60 for a year.
Pick StealthWriter if you want to evaluate properly before paying, or you work in bursts — a daily allowance suits irregular heavy use in a way a monthly word pool does not.
The claim we won't compare on
Neither tool's ability to get text past an AI detector appears above, and it is not an oversight. No vendor can observe or control the systems such a claim is about, detectors change without notice and disagree with each other on identical text, and every published bypass rate in this category was produced by the company selling the tool it tested. We publish none for our own product either — see why we publish no bypass rates.