Why We're Writing This (Transparency First)
We normally don't create comparison pages against smaller competitors. But Rephrasy has been actively running ads on our brand name and publishing comparison content designed to redirect our users. When someone searches “SupWriter” and sees a Rephrasy ad, they deserve to hear both sides.
So here's both sides. We're going to present our test data, acknowledge where Rephrasy has some advantages, and let you decide. Every claim on this page is verifiable — test both tools with the same content and see for yourself.
Rephrasy: What It Is and What It Claims
Rephrasy markets itself as an AI paraphrasing and humanization tool. Their landing page claims “undetectable AI content” and “bypass any detector.” They use a credit-based pricing model: you buy packs of credits starting at $14.99, and each humanization consumes credits based on word count.
The tool itself is straightforward. Paste in your AI-generated text, click humanize, wait 8-12 seconds, get output. There are a few settings for aggressiveness of rewriting, but the core experience is simple. Nothing wrong with the UX.
The problem is what comes out the other end.
Test Results: 58% vs 99%+
We ran our standard test suite in March 2026: 200 AI-generated essays across five subjects (literature, biology, history, computer science, and psychology). Sources were ChatGPT-4, Claude 3.5, and Gemini Pro. Each essay was processed through both Rephrasy and SupWriter, then tested against five detectors.
Rephrasy's results by detector:
- Turnitin: 54% pass rate (92 of 200 flagged)
- GPTZero: 61% pass rate (78 of 200 flagged)
- Originality.ai: 55% pass rate (90 of 200 flagged)
- Copyleaks: 60% pass rate (80 of 200 flagged)
- ZeroGPT: 62% pass rate (76 of 200 flagged)
SupWriter's results by detector:
- Turnitin: 99.2% pass rate (2 of 200 flagged — edge cases with heavy code snippets)
- GPTZero: 99.5% pass rate (1 of 200 flagged)
- Originality.ai: 99.1% pass rate (2 of 200 flagged)
- Copyleaks: 99.4% pass rate (1 of 200 flagged)
- ZeroGPT: 99.7% pass rate (1 of 200 flagged)
The gap is 41 percentage points. That's not a marginal difference — it's the difference between a tool that works sometimes and a tool that works almost always.
Why Rephrasy's Approach Falls Short
Rephrasy uses what's essentially advanced synonym replacement with some sentence restructuring. It changes individual words and flips clause order, but the underlying statistical patterns — the predictable perplexity, uniform burstiness, and consistent sentence-length distributions that AI detectors measure — remain largely intact.
Think of it like changing the paint on a car. The outside looks different, but the engine, frame, and VIN number are all the same. AI detectors don't look at the paint. They look at the engine.
SupWriter takes a fundamentally different approach. We rewrite at the statistical pattern level — varying perplexity scores, introducing natural burstiness, randomizing sentence structures the way human writers naturally do. The output doesn't just use different words; it has different mathematical properties than AI-generated text.
The Credit Pack Problem
Rephrasy's credit system sounds flexible, but it creates unpredictable costs. A $14.99 pack covers roughly 10,000 words. If you're a student humanizing a 2,000-word essay, that's five essays per pack. If you have weekly assignments across multiple classes, you're buying packs constantly.
Worse, you often need to run text through Rephrasy multiple times to get a result that passes detection (since the first pass only has a 58% success rate). Each run burns credits. Users report running text 2-3 times before it passes, effectively tripling the credit cost per piece of content.
SupWriter's model is simpler: $9.99/month, unlimited humanization. Process as many words as you need, run text as many times as you want. No credit tracking, no surprise charges when you're mid-project. And since the first pass succeeds 99%+ of the time, you rarely need a second run anyway.
Trustpilot: 1 Star vs 4.6 Stars
Rephrasy's Trustpilot score is 1 star. The recurring themes in negative reviews are:
- Output still getting flagged by detectors despite claims of “undetectable” results
- Credits running out much faster than expected
- Output quality described as “robotic” and “obviously rewritten”
- Difficulty obtaining refunds for unused credits
SupWriter's Trustpilot score is 4.6 stars. We're not perfect — the most common criticism is processing speed (under 5 seconds, but some users want instant results). But the core promise — making AI text undetectable — is consistently validated in user reviews.
Where Rephrasy Has an Edge
To be fair: Rephrasy's credit system means you only pay for what you use. If you humanize one essay per month, a single $14.99 credit pack lasts months. For extremely light users, that's potentially cheaper than SupWriter's $9.99 monthly subscription.
Rephrasy also offers a slightly larger free trial (500 words vs SupWriter's 300 words), which gives you more room to test before paying. If you want to compare both tools yourself, that extra 200 words of free testing is a genuine advantage.
Those are real advantages. But for most users — anyone processing more than one piece of content per month — SupWriter's unlimited plan at $9.99 is more cost-effective, and the 41 percentage-point gap in bypass rates makes it the obvious choice.
Our Recommendation
Test both tools yourself. Seriously. Take a piece of AI-generated text, run it through Rephrasy's free trial, run it through SupWriter's free trial, and then check both outputs with your preferred AI detector. The results will speak for themselves.
We're confident enough in our product that we encourage comparison testing. If SupWriter doesn't outperform Rephrasy in your specific use case, you should use whatever works. But for the vast majority of users and detectors, the data is clear.
Related Resources
- Best Rephrasy Alternative — Top alternatives ranked by bypass rate
- JustDone AI vs SupWriter — Another head-to-head comparison
- Best AI Humanizer Tools 2026 — Full market roundup
- Best Grammarly Alternative — For grammar and humanization
- Phrasly vs SupWriter — Budget humanizer comparison