Undetectable AI vs. Rephrasy: Beatdown
Undetectable AI continues to be the benchmark that new AI humanizers must overcome. Can Rephrasy pull off an upset?
John Angelo Yap
Updated March 11, 2025
An AI paraphrasing tool, generated with Midjourney
Reading Time: 4 minutes
You can be the smartest and most hardworking student in your campus, and still get hit with false positive AI detection. There’s no escaping this new phenomena that universities aren’t well-equipped enough to handle.
This is the world we’re living in now, and students like you must cope with that. How?
AI humanizers are a quick way to lower AI likelihood scores by paraphrasing your assignments. Let me introduce you to two of them: Undetectable AI and Rephrasy — and here’s how they stack against each other.
What are Undetectable AI and Rephrasy?
Undetectable AI and Rephrasy are AI humanizer platforms that turn any text (AI-generated or otherwise) into something that can’t be detected by detection tools. This is done through a careful rearrangement of the input, including removing common AI markers, and adding emotions and human-like errors.
We’ve reviewed Undetectable AI in the past, so make sure to check that out. Rephrasy, on the other hand, is something we’re yet to test, so I’m looking forward to seeing how it does in this comparison.
Undetectable AI vs. Rephrasy: Features
Undetectable AI’s features are what we’ve come to expect when it comes to paraphrasing tools: mostly just output customization and a built-in AI detector (to check the final version’s AI likelihood score). You can choose how the output will read based on:
- Use Case: General Writing, Essay, Article, Business Material, Marketing Material, Legal Material, Story, Cover Letter, Report
- Readability: High School, University, Doctorate, Journalist, Marketing
- Level: Balanced, More Human, More Readable
Rephrasy doesn’t have this feature (you can only select between their undetectable or SEO model). But it has a pretty unique feature wherein you can upload documents you’ve written, and the model uses it as its basis for the output.
Undetectable AI vs. Rephrasy: Readability
Original Essay | |
Chlorine is widely used to disinfect water, ensuring it is safe for drinking and other uses. It effectively kills harmful bacteria, viruses, and other pathogens, preventing waterborne diseases like cholera, typhoid, and dysentery. When added to water, chlorine reacts with organic and inorganic substances, forming byproducts such as chloramines and trihalomethanes (THMs). These byproducts, in high concentrations, can pose health risks, but their levels are strictly regulated to maintain safety. Chlorination is cost-effective and easy to implement, making it a common choice for water treatment worldwide. Despite its benefits, some people may notice a slight taste or odor in chlorinated water, though it is generally considered safe and essential for maintaining public health. | |
Undetectable AI | Rephrasy |
Chlorine is commonly used in purifying water to make it safe, for consumption and various purposes by eliminating bacteria and viruses that can cause diseases like cholera and typhoid fever When chlorine is introduced into water sources; it interacts with organic and inorganic materials to produce substances like chloramines and trihalomethanes (THMs). The presence of these byproducts in amounts can potentially lead to health concerns; however strict regulations are, in place to control their levels for safety purposes. Chlorination is often preferred for water treatment globally due, to its affordability and simple implementation.This method is widely used despite taste or odor concerns in chlorinated water because it plays a crucial role, in safeguard public health and is generally deemed safe. | Water is usually disinfected with the help of chlorine, the chemical keeps it safe to drink and for other uses. It is a really powerful agent that destroys the pathogenic bacteria, viruses, and yeasts in the water and this prevents the illnesses of the water that are caused by cholera, typhoid, and dysentery. Chlorine interacts with organic and inorganic materials upon entering the water and produces byproducts like trihalomethanes (THMs) and chloramines. In extreme concentrations, these substances threaten people's health, but safety is guaranteed by regulating their levels. The implementation of chlorination is low-cost and simple, thus it has become a popular choice in the water sector. Even though it has pros, the people might feel a little bit of flavor or a small odor in the water that has been chlorinated. |
When looking at Undetectable AI and Rephrasy’s respective outputs, it's clear that neither version maintains the clarity and precision of the original.
Undetectable AI is riddled with punctuation errors, including misplaced commas and semicolons that disrupt the flow. The sentence structure is awkward and confusing. Words like "amounts" appear without necessary qualifiers ("high amounts"). Grammatically, it struggles with consistency and creates jarring transitions.
However, it does preserve most key points from the original — only the poor execution makes it difficult to follow.
Rephrasy takes more (for the lack of a better term) creative liberties with phrasing like "illnesses of the water" instead of "waterborne diseases" and "the chemical keeps it safe" rather than explaining disinfection properly. Its grammar is better than Undetectable AI, but still features odd constructions and informal language inappropriate for an informational text.
Sentences like "it is a really powerful agent" sound unprofessional, and phrases like "the people might feel a little bit of flavor" are unnecessarily wordy, weird, and imprecise compared to the original.
Both essays are poor substitutes for the original. But if I were to pick one, Undetectable AI communicates essential information more clearly and concisely.
Undetectable AI vs. Rephrasy: AI Detection Score
Test #1
Undetectable AI: Successfully passes as human!
AI Likelihood Score: 0.1%
Rephrasy: Detected as machine-generated.
AI Likelihood Score: 100%
Test #2
Undetectable AI: Successfully passes as human!
AI Likelihood Score: 0.9%
Rephrasy: Detected as machine-generated.
AI Likelihood Score: 100%
Test #3
Undetectable AI: Successfully passes as human!
AI Likelihood Score: 21.5%
Rephrasy: Detected as machine-generated.
AI Likelihood Score: 99.9%
Test #4
Undetectable AI: Detected as machine-generated.
AI Likelihood Score: 100%
Rephrasy: Detected as machine-generated.
AI Likelihood Score: 99.2%
Test #5
Undetectable AI: Successfully passes as human!
AI Likelihood Score: 0%
Rephrasy: Successfully passes as human!
AI Likelihood Score: 14.3%
Test #6
Undetectable AI: Successfully passes as human!
AI Likelihood Score: 0%
Rephrasy: Score is too close to call.
AI Likelihood Score: 53.6%
Overall Score
Undetectable AI | Rephrasy | |
Test #1 | 0.1% | 100.0% |
Test #2 | 0.9% | 100.0% |
Test #3 | 21.5% | 99.9% |
Test #4 | 100.0% | 99.2% |
Test #5 | 0% | 14.3% |
Test #6 | 0% | 53.6% |
Average | 20.42% | 77.83% |
The Bottom Line
To be a good AI humanizer, you need to paraphrase well enough for the output to be readable and consistently avoid AI detection. Rephrasy is lacking in both regards, which is why I can’t recommend it.
At this point, I just don’t see any reason to pick any other AI bypassing tool than Undetectable AI. It’s cost-friendly, consistent, and the team behind it regularly updates their platform to provide new tools.
With all these in mind, I still feel the need to remind you to never use AI humanizers to cheat. These tools are made to avoid false positive AI detection, and not to cheat your way to graduation.
So, good luck with your assignments. If you have spare time, take time to read our other Undetectable AI articles to get a better overview. Other than that, happy writing!
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