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Undetectable AI vs. Rephrase: There's One Clear Winner

AI detection is made to guard against AI misuse, but what guards us when we're falsely accused of using AI? In this article, we'll be looking into Undetectable AI and Rephrase.info to see which one best suits your needs.
Updated March 28, 2024
A robot manipulating words, generated with Midjourney
A robot manipulating words, generated with Midjourney

As a writer, I’m confident in saying that paraphrasing text can sometimes be just as difficult as writing. I’ve always found it easier to write my own articles or stories instead of retrofitting another one to fit my use case. It’s even harder when you have goals in mind when you paraphrase text.

After the sudden rise of ChatGPT, writers became at risk for being falsely accused not only with plagiarism, but also using machine-generated text. This hyper-vigilance against LLMs have claimed student reputations and jobs around the world.

That’s how Undetectable AI rose in popularity. A tool that can tweak your text so that it bypasses detection, who wouldn’t want that? But we also have to recognize those who have been around the block for a long time like Rephrase.info. In this article, I’ll be comparing their features, fluency, accuracy, and pricing. 

What are Undetectable AI and Rephrase.info?

Undetectable AI is one of the most popular undetection tools we have today. Its main goal is to make AI-generated writing human-like. By doing so, the machine-generated writing bypasses common AI detectors. For more information, I suggest reading our full review of Undetectable AI here.

On the other hand, Rephrase.info doesn’t focus on bypassing AI detection. It’s a paraphrasing tool aimed only at rewriting your original text. While this likely means better output quality, it doesn’t have the capability to hide your text from AI detectors…or does it? We’ll find out later.

Undetectable AI vs. Rephrase.info: Features

The features of Undetectable AI goes beyond AI bypassing — it's the flexibility of its output customization. There's no need to adjust their output to fit your needs. Instead, they handle it for you. You can choose your target readability level (from high school to doctorate, marketing or journalism) and specify your use case (general writing, essay, story, cover letter, and more).

Additionally, for a monthly fee of $5, you can also use their human typing extension, allowing you to replicate human typing behavior seamlessly within Google Docs. Full review of this extension can be found here.

On the other hand, Rephrase.info offers the standard paraphrasing features such as different modes (word changer, standard, fluency, smart, creative, formal). They also offer access to 20 different languages. They even have a built-in summarizer and plagiarism checker.

Undetectable AI vs. Rephrase.info: Output Quality

Original ChatGPT Text

Our planet spins, creating a natural cycle of day and night. But keeping track of time across vast distances gets tricky. Time zones are humanity's solution, dividing the world into regions that share a standard time. Ideally, these zones follow longitude lines, with each 15 degrees representing a one-hour difference.


In reality, borders often trump perfect lines. Countries and regions prioritize consistency within their areas, leading to some zones spanning broader ranges or having unique offsets like 30 minutes. Daylight Saving Time further complicates things, adding an hour during summer months in some areas. Despite the patchwork, time zones keep our world coordinated, ensuring a shared understanding of  when that important meeting starts or that birthday message arrives.

Undetectable AI

Rephrase.info

The Earth rotates, causing the cycle of day and night. However coordinating time across distances poses a challenge. Time zones were introduced by humans to standardize time across regions. Ideally these zones align with lines, where each 15 degree increment equals one hour.


In reality national borders often influence time zone boundaries. Countries prioritize consistency within their territories resulting in some zones covering areas or having offsets, like 30 minutes. Daylight Saving Time further complicates matters by adding a hour during summer in regions. Despite the variations time zones play a role, in synchronizing our world. Ensuring everyone knows when that important meeting begins or when a birthday message will arrive.

Our planet rotates, creating a natural  day and night cycle. But keeping track of time over large distances becomes difficult. Time zones are humanity's solution, dividing the world into regions that share a common standard time. Ideally, these zones follow lines of longitude, with each 15 degrees representing a difference of one hour. 


In reality, boundaries often overwhelm perfect lines. Countries and regions prioritize consistency within their regions, causing some regions to have wider ranges or  unique time offsets such as 30 minutes. Daylight saving time further complicates matters, adding an extra hour during the summer months in some areas. Despite the differences, time zones keep our world coordinated, ensuring a common understanding of when that important meeting starts or birthday message arrives.

Let’s start with Undetectable AI, since we’ve already acknowledged its weaknesses in quality in many of our previous articles. The one thing you should know about this tool is that it openly uses errors to mimic human writing. This unfortunately means misplaced punctuations and a couple subject-verb disagreements. It looks like their output above is no exception.

I was cautiously optimistic about Rephrase.info. At the very least, I thought it’d be better than Undetectable AI’s output. The problem is, I don’t actually think it is. Even using their standard mode (rather than the default word changer mode), all it does is simply use synonyms for most of the changed parts. 

What Rephrase.info does is the very bare minimum. Sure, it’s more grammatically correct, but that’s also because it didn’t change much from the original text. What’s the point of changing “longitude lines” to “lines of longitude”? Or “one-hour difference” to “difference of one hour”?

If you’re just a paraphrasing tool and nothing else, you better be damn good at paraphrasing. Rephrase.info, unfortunately, is not.

Undetectable AI vs. Rephrase.info: AI Likelihood Scores

Test #1

Undetectable AI: Identified as machine-generated.
AI Likelihood Score: 100%

Rephrase.info: Identified as machine-generated.
AI Likelihood Score: 100%

Test #2

Undetectable AI: Identified as human.
AI Likelihood Score: 0.1%

Rephrase.info: Identified as machine-generated.
AI Likelihood Score: 100%

Test #3

Undetectable AI: Identified as human.
AI Likelihood Score: 0%

Rephrase.info: Identified as machine-generated.
AI Likelihood Score: 100%

Test #4

Undetectable AI: Identified as human.
AI Likelihood Score: 0%

Rephrase.info: Identified as machine-generated.
AI Likelihood Score: 99.8%

Test #5

Undetectable AI: Identified as human.
AI Likelihood Score: 0%

Rephrase.info: Identified as machine-generated.
AI Likelihood Score: 92.3%

Test #6

Undetectable AI: Identified as human.
AI Likelihood Score: 0%

Rephrase.info: Identified as machine-generated.
AI Likelihood Score: 98.8%

Final Tally

Test Number

Undetectable AI

Rephrase.info

Test #1

100%

100%

Test #2

0.1%

100%

Test #3

0%

100%

Test #4

0%

99.8%

Test #5

0%

92.3%

Test #6

0%

98.8%

Average AI Likelihood

16.68%

98.48%

Undetectable AI vs. Rephrase.info: Pricing

Undetectable AI is a subscription service that increases depending on how many words you need in a month. It starts at $9.99 per month (or $5 per month if you pay annually) for 10,000 words and increases up to $209 per month ($104.42 per month if you pay annually) for 380,000 words.

Rephrase.info’s main three modes (word changer, fluency, standard) are all free. If you want to unlock more modes and no ads, you can get their premium plan for:

  • $7 per week.
  • $20 per month.
  • $150 per year.

The Bottom Line

Maybe for the first time ever in one of my reviews, I’m going to be completely blunt. There is absolutely no reason to use Rephrase.info, let alone subscribe to their paid plans.

Like I said earlier, if you’re going to market your tool as a paraphraser, you need to be good at paraphrasing. All Rephrase.info does is take small parts of your original text and slightly tweak it through synonyms or rearrangements. Add that to the fact that it doesn’t even bypass AI detection, and you’ve got a recipe for disaster.

On the other hand, Undetectable AI has its own share of flaws but you can easily overlook this because it does its job as a bypasser accurately. It’s also the superior paraphraser because of the fact that it actually tries to create original text compared to the bare minimum that is Rephrase.info.

So, in this head-to-head battle, there’s one clear winner: Undetectable AI. If you want to learn more about this product, I suggest reading one of our many articles about it. Good luck!

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Written by John Angelo Yap
Hi, I'm Angelo. I'm currently an undergraduate student studying Software Engineering. Now, you might be wondering, what is a computer science student doing writing for Gold Penguin? I took up studying computer science because it was practical and because I was good at it. But, if I had the chance, I'd be writing for a career. Building worlds and adjectivizing nouns for no other reason other than they sound good. And that's why I'm here.
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