The rise of powerful AI language models like GPT-3 has made it easier than ever to generate human-like text. While AI writing tools can be immensely helpful for content creators, they also open the door for potential misuse. Students could use AI to cheat on essays, spammers could auto-generate fake reviews and comments, and unscrupulous marketers could publish AI-written articles stuffed with keywords to game search engine rankings.
This is where AI content detectors come in. These tools analyze a piece of text and predict the likelihood that it was generated by AI rather than written by a human. While not 100% accurate, the best AI detectors can reliably flag suspicious content that warrants a closer look.
I tested over 20 of the most popular AI content detectors by feeding them samples of human-written text as well as text generated by OpenAI‘s GPT-3 model. I evaluated them based on accuracy, ease of use, and extra features. Here are my picks for the top 10 free AI content detectors:
1. Writer.com AI Content Detector
https://writer.com/ai-content-detector/
Writer.com‘s detector is my top pick for its combination of accuracy, simplicity, and generous free usage limit. It correctly identified the GPT-3 sample as AI-generated and the human-written sample as likely human-generated.
The interface couldn‘t be simpler – just paste your text and click a button for an instant analysis. You get a clear percentage score indicating the likelihood the text is AI-generated vs human-written. The free version allows up to 1500 characters at a time, which is enough to check a couple meaty paragraphs.
One thing I love is the "Edit text" button, which lets you iteratively revise the content and re-check it until the AI score goes down. This can be really handy if you‘re using AI writing tools and want to substantially edit the output to make it read as more human-like.
While Writer.com‘s detector may lack some of the bells and whistles of other tools on this list, I found its straightforward accuracy and usability to be a winning combination. Give it a try for your AI content detection needs.
2. Content at Scale
https://contentatscale.ai/ai-content-detector/
Content at Scale‘s detector has an impressive 25,000 character limit for free usage. It breaks down the results into multiple scores: Perplexity, Burstiness, Variety, and an overall Human-Written Score.
When I tested it, the human-written sample got a 99% Human Score while the GPT-3 sample got an 80% Human Score. So while it leaned in the right direction, it wasn‘t quite as decisive as Writer.com in identifying the AI text.
The Burstiness score presumably looks at the text‘s information density, while the Variety score seems to consider vocabulary diversity. These extra metrics provide some interesting insights but interpreting them takes a bit more effort compared to the simple percentage scores most other detectors provide.
3. Copyleaks
https://copyleaks.com/features/ai-content-detector
Copyleaks is primarily a plagiarism checker, but they‘ve recently added AI content detection as a free add-on feature. The interface is a bit clunky, as you have to create an account and make a couple clicks to get to the AI analysis.
Rather than an overall score, Copyleaks provides a color-coded analysis where it highlights different sentences and assigns them individual probability scores for being AI-generated. So you have to sort of eyeball the results to get an overall sense.
When I tested it, the human-written text got AI probability scores of 2-3% for each sentence, while the GPT-3 sample had sentences scoring anywhere from 20% to 80%. So it seemed fairly accurate, but I found myself wishing for a clearer way to interpret the overall results.
4. GPT-2 Output Detector
https://huggingface.co/openai-detector
This detector from Hugging Face is unique in that it‘s specifically designed to detect output from OpenAI‘s GPT-2 model, rather than more recent models like GPT-3. So it‘s a bit less relevant today, but still interesting to try.
The human-written sample got a 99.9% chance of being human-written, while the GPT-3 sample was rated as having a 97% chance of being AI-generated. Interestingly, the GPT-3 text still got a high AI probability score even though this detector is tuned for GPT-2. This shows there are some common tells that can identify machine-generated text across different models.
Unfortunately, the UI is very bare bones and there‘s a limit of only 512 tokens per query (a few paragraphs). So while it performed well, the limited customization for more recent AI models makes this one less practical as a go-to tool compared to some others on the list.
5. ZeroGPT
https://www.zerogpt.com/
ZeroGPT provides a clean, simple interface with clear results. It rates the text on a scale from "Your Text is Very Unlikely to be AI-Generated" to "Your Text is Likely to be AI-Generated". When I tested it, the human-written text got the lowest AI likelihood rating while the GPT-3 sample was rated as likely to be AI-generated.
One nice touch is that it color-codes individual sentences to highlight ones that are highly likely to be AI-generated. It also provides an overall "fakeness" score from 0-100%. The GPT-3 sample got a fakeness score of 75% while the human text got 0.16%.
There were no obvious restrictions on text length, which is great for checking longer articles. Overall ZeroGPT is a solid, easy to use tool that I‘d recommend trying, though its accuracy wasn‘t quite on par with Writer.com in this test.
6. GPTZero
https://gptzero.me/
Launched in early 2022, GPTZero was one of the first AI content detectors to gain widespread attention. It was created by a college student to help teachers identify essays written by AI.
The tool has a simple, clean interface. It analyzes your text and returns two scores: "Perplexity" and "Burstiness". Perplexity measures the complexity and randomness of the text, while burstiness looks at variations in sentence length.
In my testing, GPTZero rated the human-written text as "Your text is very likely to be human-written", while the GPT-3 sample was identified as "likely to be written entirely by AI". However, both samples returned perplexity and burstiness scores in the green range, so the evidence for the AI determination was not totally clear-cut.
It allows up to 5,000 characters to be checked at once, which is sufficient for most use cases. More than some tools but less than others. One nice feature is the WordPress plugin that lets you automatically scan your drafts for AI content before publishing.
7. Sapling
https://sapling.ai/utilities/ai-content-detector
Sapling‘s detector has a streamlined UI that‘s very quick and easy to use. It took all of five seconds to analyze the test samples. The human-written text was scored as 99% likely to be human-generated, while it was 100% confident the GPT-3 sample was machine-generated.
It provides a simple percentage breakdown showing how much of the text is likely human vs AI. But it doesn‘t give any additional insights or the ability to dig deeper into which parts of the text are suspicious.
The 2,000 character limit is serviceable but a bit lower than some other free tools. You can subscribe to a paid plan for increased limits and to remove the Sapling branding from the results page.
8. Originality.AI
https://originality.ai/ai-content-detector
Originality.AI is a paid plagiarism checker and AI detector, but it offers a limited free plan with up to 5,000 words per month. It provides a clear "Content Authenticity Score" from 0-100, with higher being more likely human-generated.
The human-written sample got an impressive 99% authentic score. Oddly, the GPT-3 sample also scored 99% authentic, indicating the detector was fooled by the AI text. This seems to be an outlier though, as most online reviews suggest Originality.AI is usually reasonably accurate.
The UI has a polished feel and the flow is intuitive. The results include a couple helpful extras like a spam score, spelling and grammar check, and a list of any plagiarism detected.
While the generous word count allowance is great, at the end of the day what matters most is detection accuracy. Originality.AI came up short in this area compared to top performers like Writer.com in my testing. However, the full paid version may perform better with more training data.
9. CrossPlag AI Content Detector
https://crossplag.com/ai-content-detector/
CrossPlag‘s detector did a solid job of identifying the GPT-3 sample as very likely to be AI-generated. It provides a clear percentage breakdown: 81% likely AI, 19% likely human for the machine text. Whereas the human-written sample was scored as 99% likely to be human.
The free version appears to be unlimited, with no cap on number of checks. However a notice indicates that it‘s "meant for illustrative purposes only" and that the full paid version offers improved accuracy.
CrossPlag loses some points for usability. After pasting your text, you have to manually click to enable the AI detection. The percentage results are presented clearly, but there‘s no detailed sentence-by-sentence analysis. Overall, not a bad tool but not quite as polished as some others.
10. Corrector App
https://corrector.app/ai-content-detector/
Rounding out the list is Corrector App‘s detector. The good: it offers a generous 25,000 character limit for free, and the UI is clean and simple. It provides both an overall percentage score as well as a hashtag-shaped visual of how the AI probability ebbs and flows over the course of the text.
The not-so-good: it wasn‘t very accurate in my testing. It gave the human-written sample an AI probability score of 37%, indicating it was somewhat unsure about its origin. With the GPT-3 sample it did better, scoring it as 63% likely to be AI-generated. But I‘d hope for more definitive results when the input text is 100% machine-generated.
Corrector App is still in beta, so it may well improve over time as more training data helps refine the model. But for now, you‘re probably better off using one of the more tried and true tools higher up the list for the most dependable AI content detection.
Limitations of AI Content Detectors
As you can see from the test results, even the best AI content detectors available today are not 100% foolproof. Most tools still struggle to consistently identify text generated by the latest AI models like GPT-3 and ChatGPT. As the detectors get better, you can bet the AI writing tools will also keep advancing to evade detection.
AI content detectors work by looking for patterns and quirks commonly found in machine-generated text, like repetitiveness, simplistic sentence structures, and so on. But as the AI models ingest ever-larger datasets and grow more sophisticated, their output becomes harder and harder to distinguish from human writing.
It‘s also important to note that a piece of text getting a high AI probability score doesn‘t automatically mean it‘s "bad" or attempting to deceive. There are plenty of legitimate reasons to use AI writing tools, like generating ideas, creating first drafts, or personalizing content at scale. As with any technology, it‘s all about how you use it.
Likewise, content that reads as very "human-like" is not always higher quality or more trustworthy. Skilled human writers can still produce inaccurate, misleading, or spammy content. Critical thinking skills and fact-checking are essential for evaluating any information you find online, regardless of its presumed origin.
The Future of AI Content Detection
Looking ahead, I believe AI content detectors will remain a valuable tool even as they continue to play catch-up with ever-improving AI writers. Much like spam filters or plagiarism checkers, they can be a helpful first line of defense in flagging suspicious content for closer review.
Teachers can use detectors to identify students who may be cheating on assignments. Publishers, moderators and SEO professionals can spot auto-generated spam and misinformation. And companies can monitor for fake AI-generated reviews, comments and other content that aims to mislead.
As the detectors integrate larger language models and more advanced machine learning architectures, their accuracy should keep improving over time. We may also see the emergence of industry-specific detectors trained on narrower datasets to identify AI content in specialized domains like law, medicine, or academia.
At the end of the day, the best approach is likely a combination of technological assistance and human judgment. Tools like Writer‘s AI Content Detector can highlight passages that warrant a closer look – but there‘s no full replacement for critical reading and thinking skills. The goal is to have thoughtful, well-researched writing – regardless of whether it comes from a human or a machine.
