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8 Best AI Detectors: List of Tested and Reviewed
Writing with AI
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8 Best AI Detectors: List of Tested and Reviewed

Looking for an AI detector you can rely on? Check out our list of the top 8 AI detection tools and see how they compare in accuracy, pricing, and features.
What Is the Best AI Detector
Written by
Catherine B.
Published on
May 23, 2025
Table of contents
AI has come to stay. Worldwide, 86% of students use AI in their studies, with 24% admitting they generate the first draft using AI writing tools like ChatGPT.
The pushback from the academic institutions was only a matter of time. A number of them prohibited the use of AI-generated content in the submitted papers. Turnitin, the flagship originality detector among U.S. colleges and universities, now runs AI checks by default.
So, you’d better check papers for AI content. But what is the best AI detector? Check out the eight best free AI detectors you should try, from StudyPro to Undetectable AI.

Why You Should Care About AI Scans

If you know you wrote your paper yourself, you have nothing to worry about, right? Well, not exactly. Even if you write a paper from scratch, AI content detectors may produce false positives, with texts written by non-native speakers more likely to get flagged as AI-written content.
Of course, there’s also the question of academic integrity among both educators and students. If some students submit AI-generated papers as their own, they violate the core principle of any educational institution: academic honesty.
On top of that, over-relying on generative AI tools hinders students’ learning progress. With AI, students might be essentially outsourcing analysis, synthesis, and creativity to algorithms, and thus failing to develop those skills themselves.
But how can professors detect Chat GPT? AI tool output is often virtually indistinguishable from human-written content. Luckily, AI content detectors can help educators identify AI-generated content and do so at scale.

5 Markings of a Good AI Detection Tool

When we set out to identify the top AI detection tools for students, we had to come up with five criteria that characterize a good one:
  • High accuracy. The whole point of this is to distinguish between AI-generated and human-written content, so it must do it well.
  • Low false positives. To avoid false positives, the tool must account for diverse writing styles.
  • Proper results breakdown. Just like a plagiarism detector highlights plagiarism examples, an AI detector tool should show you which sentences are deemed AI-generated.
  • Transparency. If the company behind the tool doesn’t disclose how its AI content detector works or what AI models it can detect, that’s a red flag.
  • Versatility. A good AI detection tool supports a wide variety of AI models, from OpenAI models to Claude and Gemini.

8 Best AI Detectors to Consider in 2025

So, what is the best AI detector? Well, that depends on your priorities as a user. Here’s your snapshot of our eight contenders:
Tool
Is best..
StudyPro
for powerful and completely free AI detection
QuillBot
for multi-language support
Grammarly AI detector
for user-friendly interface
Turnitin
for educators and institutions
Smodin
for hassle-free file upload
Originality AI
for website owners, marketers, and publishers
Winston AI
for feature-packed subscription
Undetectable AI
for cross-tool AI probability score
Wonder, “How do AI detectors work?” In a nutshell, they break the text down into chunks and look for patterns in the sentence structure and word choice typically used by AI models.

StudyPro AI Detector

StudyPro AI Detector
Pricing: Free (during beta)
Target audience: Students looking for an all-in-one academic writing tool
Key features:
  • Multiple AI detectors available within a single platform
  • High accuracy and low false positives
  • Detailed breakdown of which paragraphs are likely to be AI-generated
  • AI detection algorithms regularly updated to keep up with the latest AI models
  • No free version limits during beta
StudyPro was conceived as a versatile tool that streamlines academic writing from outlining and drafting to — you guessed it — originality and AI content checks. Unlike most AI tools, StudyPro was trained exclusively on academic papers and reliable sources, so you can trust its output.
And the best part? StudyPro is completely free during its beta, making it one of the best free AI detection tools on the list.
Here’s how StudyPro fared in our testing:
  • AI-generated content: Accurately detected AI-written text generated by Claude, Gemini, and ChatGPT (GPT-4)
  • Human-written content: Accurately identified three samples of human-written content without any false positives
  • Mixed content: Mostly managed to distinguish between AI-generated and human-written paragraphs in all three samples
StudyPro AI Detector
Verdict: StudyPro is the best AI detector if you’re looking for a checker that is seamlessly integrated into your AI-enhanced writing workflows.

QuillBot’s AI Detector

QuillBot’s AI Detector
Pricing: $8.33/month (billed annually); free plan available
Target audience: Students and researchers
Key features:
  • AI content detection for multi-language texts (English, French, Spanish, German, Dutch)
  • Free version limit of 1,200 words per check
  • Separate scores for AI-generated, AI-generated & AI-refined, human-written & AI-refined, and human-written content
  • Sentence-by-sentence AI score breakdown
QuillBot is another platform that positions itself as an all-in-one AI toolkit for students. You’ll find its AI content detector side by side with a plagiarism checker, AI humanizer, and paraphrasing tool.
Here’s how QuillBot fared in our testing:
  • AI-generated content: Correctly identified AI-written content from Claude, GPT-4, and Gemini, with all three samples scored as 100% AI content
  • Human-written content: Identified all three samples as 0% AI-generated content
  • Mixed content: Incorrectly identified all three samples as 0% AI-generated, even though they contained unedited GPT-4 output
QuillBot’s AI Detector
Verdict: QuillBot is one of those AI detector tools that are suitable for simple checks of short texts. You might find it useful if your texts are in various languages or if you don’t want to create an account to run a quick check. However, don’t count on it to accurately detect a mix of human-written and AI content.

Grammarly AI Detector

Grammarly AI Detector
Pricing: $12/month (billed annually), free checks available
Target audience: Professional content writers, educators, students, and business teams
Key features:
  • Free AI content detection for texts up to 10,000 characters
  • No account required for free checks
  • Detailed sentence-by-sentence breakdown (premium users only)
  • User-friendly interface, especially if you’re already using Grammarly
Yes, you may know Grammarly as a proofreading tool, but it also offers an AI detector. Grammarly can detect AI-generated content produced by Gemini, ChatGPT, and Gemini and returns a percentage score.
Here’s how Grammarly fared in our testing:
  • AI-generated content: Failed to accurately detect 100% AI-generated content, with scores at 73% for Gemini, 56% for Claude, and solely 25% for ChatGPT texts
  • Human-written content: Inaccurately flagged human-written content as partially AI-generated in one case out of three (the score was 16%)
  • Mixed content: Failed to detect AI-generated content at all, tagging all three samples as fully human-written
Grammarly AI Detector
Verdict: Thanks to its generous 10,000-character limit, Grammarly had the potential to be one of the best free AI detectors, but its accuracy leaves much to be desired.

Turnitin AI Checker

Turnitin AI Checker
Pricing: On demand
Target audience: Educational institutions
Key features:
  • AI scores below 20% not displayed to avoid false positives
  • Separate scores for AI-generated content and AI-generated and AI-paraphrased text
  • Sentence-by-sentence breakdown
  • AI scores displayed only to educators
Turnitin, a premier originality detection software for U.S. educational institutions, launched its AI detection tool in 2023, with AI scans running by default on every paper submitted to it. The company is quite transparent about its AI checker model and has even published a whitepaper on its architecture and testing protocol. It also admits it might miss up to 15% of AI content to prevent false positives.
However, some educational institutions chose to disable the automatic AI content detection (case in point: Vanderbilt). The reason: false positives, especially in the case of texts written by non-native English speakers.
Turnitin AI Checker
Verdict: If you’re looking for an AI detector tool, Turnitin is a viable option only if you’re an educator at an institution that already uses it for checking assignments. If you’re a student and have access to Turnitin, you won’t be able to see your AI score.

Smodin

Smodin
Pricing: Starts at $9/month (billed annually)
Target audience: Students, content writers, businesses, universities
Key features:
  • Basic AI detection capabilities available for free (up to 5,000 characters, five free scans per week)
  • Sentence breakdown available (premium users only)
  • File upload for AI content detection (.docx, .doc, .pdf)
Smodin is an AI writing assistant for students and content creators alike that offers a free (albeit limited) AI detector. Unlike most tools on our list, however, Smodin can determine AI-generated content and human-written text only.
Here’s how Smodin fared in our testing:
  • AI-generated content: Incorrectly labeled ChatGPT output as 28% AI-generated text and Claude output as 68% AI-generated, while identifying Gemini content as 100% AI-written content
  • Human-written content: Correctly identified all three samples as fully human-written content
  • Mixed content: Incorrectly identified all three texts that combined human-written and AI-generated passages as 100% human-written
Smodin
Verdict: Smodin isn’t the most accurate AI detector out there. It tends to produce a lot of false negatives, and its limited free version leaves much to be desired. That said, you may find the file upload quite convenient.

Originality.ai

Originality.ai
Pricing: Starts at $12.95/month (billed annually) or $30 as a one-time payment (pay-as-you-go)
Target audience: Content marketers, writers, publishers, website owners
Key features:
  • GPT-4o, Claude 3.5, Llama 3.1, ChatGPT, and Gemini Pro content detection
  • File upload and URL import (premium users only)
  • Free lite checks for texts of up to 750 words
  • Confidence score instead of AI-generated text share
Originality AI offers more than an AI content detection tool. The platform also comes with plagiarism detection and a fact checker, along with a Chrome extension, API integration, and even a WordPress plugin.
It is upfront about being built for content writers and website owners, not students. So, if you’re wondering how to make your essay not AI detectable, Originality AI is probably not the tool for you.
Here’s how Originality AI fared in our testing:
  • AI-generated content: Correctly flagged AI-written content as 100% AI-generated
  • Human-written content: Correctly identified human-written content in all three cases
  • Mixed content: Incorrectly provided a 100% human-written confidence score for all samples
Originality.ai
Verdict: Originality.ai is a good tool for verifying that your blog posts, website copy, and other online content are completely human-written.

Winston AI

Winston AI
Pricing: Starts at $12/month (billed annually), free plan available
Target audience: Content writers, students, teachers
Key features:
  • Legacy AI content detection for previous ChatGPT models
  • Advanced AI model detection even on the free plan
  • ChatGPT, Claude, Google Gemini, Llama, Jasper content detection
  • Multi-language support across seven languages, including English, Spanish, and Chinese
Winston AI is an AI detector that can detect AI, human-written, and AI+human content. In addition to AI-generated text, Winston AI can also detect AI-generated images and deepfakes. Under its free plan, you can run a check on up to 2,000 words, but only while your free trial is ongoing.
Here’s how Winston AI fared in our testing:
  • AI-generated content: Correctly identified all three samples as over 98% AI-generated
  • Human-written content: Scored fully human-written samples as 94%, 96%, and 97% human
  • Mixed content: Incorrectly scored the samples as almost fully human-written, with scores exceeding 95% in all three cases
Winston AI
Verdict: Winston AI offers you a wide range of features and relatively accurate results for purely AI-generated or human content. But if you’re looking for a free checker (even a limited one) you can use regularly, this tool isn’t it.

Undetectable AI

Undetectable.ai
Pricing: Starts at $10/month (billed annually)
Target audience: Content writers and students looking to bypass AI checks
Key features:
  • AI detection likelihood across multiple tools (including QuillBot, Grammarly, GPTZero, and Sapling)
  • Overall human score and AI probability score
  • AI humanizer available within the same interface
  • Sentence breakdown of the probably AI-generated text
If you’re dismayed by just how disparate AI check results can be across multiple tools, Undetectable AI was created for you. It returns the AI detection likelihood score across multiple AI checkers, including some of the ones we mentioned on this list.
Here’s how Undetectable AI fared in our testing:
  • AI-generated content: Correctly identified Gemini, ChatGPT, and Claude content with 95+% AI probability score
  • Human-written content: Falsely flagged human-written samples as 58%, 61%, and a whopping 80% AI-generated
  • Mixed content: Identified the AI content correctly, but mistakenly flagged some human-written paragraphs as AI-generated
Undetectable.ai
Verdict: Undetectable AI is worth looking into if you’re an unapologetic generative AI user and want to make your use of tools like ChatGPT undetectable. That said, false positives are rampant with this tool.

In Closing

So, what is the best AI detector? Well, the final verdict depends on your particular needs. You might value free access above everything else, for example. Or, you might be willing to pay a subscription fee, but you’d want a detailed sentence breakdown and multi-language support.
That said, there is one AI detector that turned out to be the most accurate one in our testing: StudyPro. So, if you’re looking for a dependable AI detector packaged into a powerful AI-powered academic writing tool, check it out!

Frequently asked questions

In our testing, StudyPro turned out to be the most accurate AI detector: it correctly identified AI-generated, human-written, and mixed content. All other AI content detectors notably struggled with mixed texts that combined AI-generated and human-written passages.
That said, if we’re taking into account the results of only running scans on purely AI-generated or human-written text, Originality.ai and QuillBot also showed accurate results.
Which AI detector is the best one depends on what you expect it to do. For example, StudyPro offers an AI checker that will seamlessly integrate into your academic writing workflows. Undetectable.ai, on the other hand, will give you an idea of how your text may perform with different AI detectors.
Some of the best AI detectors we tested include:
  • StudyPro
  • QuillBot
  • Grammarly AI detector
  • Turnitin
  • Smodin
  • Originality.ai
  • Winston AI
  • Undetectable.ai
They can work, but only up to a point. For example, in our testing, most AI content detectors struggled with accurately detecting AI content within texts that combined both AI-generated and human-written paragraphs. In some cases, AI content detection tools may also mistake human-written content for AI text and vice versa.
So, we’d advise you to test an AI detection tool yourself before starting to rely on it and take its results with a grain of salt.
Sources:
  1. Coley, M. (2023, August 16). Guidance on AI detection and why we’re disabling Turnitin’s AI detector. Vanderbilt University. https://www.vanderbilt.edu/brightspace/2023/08/16/guidance-on-ai-detection-and-why-were-disabling-turnitins-ai-detector/
  2. Survey: 86% of students already use AI in their studies -- campus technology. (2024, August 28). Campus Technology. https://campustechnology.com/articles/2024/08/28/survey-86-of-students-already-use-ai-in-their-studies.aspx
  3. Turnitin. (2024, October 18). Turnitin’s AI writing detection model architecture and testing protocol. https://www.turnitin.com/whitepapers/turnitin-ai-writing-detection-model-architecture-and-testing-protocol
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