Undetectable, Copyleaks, and ZeroGPT: 3 AI Detectors Compared

The We-Right team tested three leading AI detectors – Undetectable, Copyleaks, and ZeroGPT – to assess their performance on real texts. Although our review may include affiliate links, you can be assured that all insights are accurate and created with strict editorial standards.

The AI-powered writing tools are growing at a 25% CAGR, and the worldwide AI market is projected to surpass $826 billion by 2030. Meanwhile, AI writing raises several ethical concerns, such as the potential for plagiarism and the devaluation of original content. That’s why content creators use different AI detectors to determine whether the text is artificially generated. In this article, we will examine three of the most popular AI detectors – Undetectable, Copyleaks, and ZeroGPT – and compare their features.

Is AI Detection Important?

AI writing models have become advanced enough to replicate tone, voice, and even emotional nuance. While they can save time and sometimes improve content quality, their widespread use raises ethical questions. Additionally, Google now flags AI-generated content that appears low-effort or robotic as of poor quality. Pages consistently marked this way can see their SEO and SERP rankings suffer over time.

To find out whether content was generated by artificial intelligence, you can use an AI detector. These tools analyze word patterns, sentence structure, predictability, and complexity using machine learning to estimate whether a human or an AI wrote a text. Three popular services for detecting AI content are Undetectable, Copyleaks, and ZeroGPT. Let’s learn more about them.

About Undetectable

Undetectable is a platform that combines AI detection, humanization, and content creation. These are the key features of Undetectable:

• AI Detector. Use this feature to figure out whether your content is flagged as AI-generated. It’s simple to use, as you just paste your content into the tool, and the results appear almost instantly. The Undetectable service identifies AI-generated content from 8+ platforms, including ChatGPT, Gemini, Claude, and others.
• AI Humanizer. The humanizer service modifies content that has not passed AI Detectors to make it appear more human-written and less likely to be detected. It’s simple to use: paste your text, click the «Humanize AI Text» button, and Undetectable adds and adjusts sentences to imitate the characteristics of real human writing.
• AI Translator. Undetectable offers a free English-to-Spanish translation tool. It’s done directly in the browser with no downloads required.
• AI Job Application Bot. This Undetectable tool simplifies the job search by creating customized resumes from your existing one or your LinkedIn profile. It helps you personalize your job search with filters to find the most suitable roles and automates your job applications.
• AI SEO Writer. The service helps you churn out a high volume of keyword-researched articles quickly – all you have to do is answer a couple of questions about your audience and desired keywords.

Undetectable is trusted by leading organizations, including Business Insider, Forbes, ABC, BuzzFeed, CBS, FOX, NBC, BBC, and Nature.

Undetectable – Pricing

Undetectable has a free plan that allows you to check up to 10,000 words for free. Users interested in the advanced features of this AI detector can subscribe on a monthly or yearly basis. Typically, the annual subscription comes with a 50% discount.

These are the basic features available after purchasing a subscription:

• Passes AI detectors;
• High quality, legible content;
• Watermark and future-proof;
• Unlimited Human Auto Typer;
• Unlimited AI Detecting;
• Access to Smart Job Applier;
• AI Question Solver;
• Writing Level Matching;
• API Compatible.

Our Experiment with the Undetectable Service

We decided to check out how accurately the Undetectable service identifies the AI-generated content. First, we have input 100 words of the human-written text. As you can see, the Undetectable service accurately pointed out the text as human-written content.

The next step involved inputting the tweaked version of the content made by the AI service. As you can see from the screenshot below, Undetectable was one of the AI detectors to flag the text as AI-generated content.

About Copyleaks

Copyleaks is a service designed to detect AI-generated content and plagiarism. It’s widely used by students, educators, and professionals who want to ensure their work is original and credible. The key features of Copyleaks include:

• AI Detector API. The AI Detector API is a flexible and scalable solution for businesses, allowing straightforward integration into existing systems. It enables real-time content verification, ensuring accurate detection of AI-generated content.
• AI Detector Browser Extension. The AI Detector Browser Extension enables users to instantly verify the authenticity of content as they browse.
• LMS AI & Plagiarism Detector Integrations. The LMS Integration allows educational institutions to automatically scan for plagiarism and AI-generated content within their Learning Management Systems.
• GenAI Governance for Marketing. GenAI Governance helps marketing organizations adopt generative AI responsibly by integrating governance controls to mitigate risks.

Copyleaks – Pricing

The Copyleaks service offers a couple of free scans per day. You can also subscribe to the premium plan to access more advanced AI checks and spend more credits daily. There are 250 words in 1 credit. For example, if the text submission you have uploaded has 251 words, 2 credits will be deducted from your account. These are the basic features of a premium subscription plan:

• Pause your account at any time;
• Plagiarism detection is available in over 100 languages, and AI detection is available in over 30 languages;
• Detects multiple forms of paraphrasing, such as direct and indirect paraphrasing, plus content that has been put through a text spinner;
• Detection of the most popular AI models, including ChatGPT, Gemini, and Claude, with over 99% accuracy;
• Two users included.

Our Experiment with the Copyleaks Service

We have started our Copyleaks test by inputting the exact 100 words of the human-written text that we used in our Undetectable experiment. As you can see, Copyleaks is one of the AI detectors that accurately identifies human-written content.

The tweaked version of the text was accurately flagged as AI-generated content. This allows us to conclude that Copyleaks is one of the AI detectors that analyzes content with great accuracy.

Read also our article: QuillBot Review: 7 Things You Need to Know Before Using It

About ZeroGPT

ZeroGPT is a free AI text detection instrument for students, educators, and other professionals that allows users to upload files or paste text to check for artificially created content. While the site is easy to navigate and provides immediate results, the service’s accuracy is sometimes inconsistent, often mislabeling human-written text as AI-generated and struggling with certain types of generated content, raising questions about whether it can be considered one of the best AI detectors. ZeroGPT analyzes text based on 2 characteristics: «perplexity» and «burstiness»:

• Perplexity. How random your text is based on predictability. The model runs text through GPT-2 (345 million parameters). The range of perplexity is not reasonably known. Still, values closer to 0 are very likely to be artificially generated, while those closer to 100 have a higher chance of being human-written.
• Burstiness. The occurrence of non-common items appearing in random clusters over time (aka creative variability). Perplexity is uniformly distributed and consistently low for machine-generated content. As humans naturally include more variability in our writing, you’ll notice it has a lower chance of being predicted by patterns.

ZeroGPT – Pricing

ZeroGPT can be used for free if you only want to check whether your content is human-written or AI-generated. For more advanced features, consider the premium plan, which comes in three versions: Pro, Plus, and Max.

On the Max subscription plan, these are the features included:

• Enjoy a Pro Experience without ads;
• 150,000 Characters per AI detection;
• 75 Batch files check for AI detection;
• Generate PDF report for AI detection;
• History of all your detections (text not included);
• 3,500 Prompts in ZeroCHAT-5;
• 40,000 Words in Plagiarism Checker per month;
• 10,000 Words in AI Summarizer;
• 5,000 Words in AI Paraphraser;
• Paraphrase in Unlimited Modes;
• 10,000 Words in AI Grammar & Spell Check;
• 3,000 Words in AI Translator;
• Generate Emails & Replies with AI;
• Access ZeroGPT on WhatsApp and Telegram.

Our Experiment with the ZeroGPT Service

ZeroGPT is the first AI detector on the list that hasn’t recognized our fully human-written text. Even though the ZeroGPT service stated that «the text is likely human-written», the percentage of AI is still high – 61.94%, which is way more than an acceptable value to mark the text as authentic content.

Surprisingly, the completely AI-generated version of the text was marked as human-written with a low AI percentage of 14.5%. Based on this, the analysis of ZeroGPT might be unreliable.

In our opinion, a good approach is to utilize ZeroGPT in conjunction with other reliable AI detectors to identify generated content with maximum precision. The service also features a handy paraphraser tool that helps remove AI-generated constructions in the text and make it appear more human-written.

Undetectable, Copyleaks, and ZeroGPT AI Detectors: A Comparative Table

Now, let’s summarize the things we discussed earlier and consider how the most popular AI detectors differ from each other. Check the comparative table below.

Final Words on AI Detectors

After testing all three tools, we can clearly highlight the strengths and weaknesses of each. Undetectable proved fast and accurate in spotting AI-generated text and offers additional tools, such as a Humanizer, although the rewritten output still requires polishing. 

Copyleaks has become the most practical solution for our team – it is accurate in both AI and plagiarism detection, works well with long texts, and supports multiple languages, making it ideal for international projects.

ZeroGPT, while a bit less reliable in accuracy, remains useful thanks to its free, unlimited checks, making it a handy option for quick, budget-friendly screening. We recommend using ZeroGPT alongside other reliable detectors to achieve optimal accuracy in determining whether the content is machine-generated or human-authored.

Ultimately, the choice depends on your priorities: if you require precision and professional features, Copyleaks (and to some extent Undetectable) are better options. If your focus is on free access for quick checks, ZeroGPT still has value. For us at We-Right, Copyleaks is the service that meets all our main criteria – reliability, flexibility, and multilingual accuracy.

Frequently Asked Questions About AI Detectors