I tested 5 AI writing detectors—one was nearly perfect, one completely missed the mark

AI Writing Detection: Testing 5 Apps to Find the Best and the Worst

AI tools like ChatGPT, Google Gemini, and DeepSeek have become essential for writers. They help with everything from drafting emails to summarizing content and analyzing tone. Since late 2022, these AI assistants have saved countless hours by handling writing tasks quickly and efficiently. Need a cover letter? AI can deliver one in seconds, complete with a greeting and a tailored summary of your experience.

However, AI-generated writing often shows predictable patterns—lack of originality, vague details, and repetitive phrasing. At the same time, AI is getting smarter. For instance, ChatGPT can rewrite text to sound more unique and avoid detection by tools like GPTZero. This ongoing back-and-forth between AI writing and detection feels like a cat and mouse game with no clear winner.

If you’re a writer, whether crafting content for work, school, or personal projects, knowing how well AI writing detectors perform can be useful. I tested five popular AI detection apps over a week, using three types of text: a chapter from a book, a ChatGPT-generated cover letter written with flair to avoid detection, and a half-human, half-AI article completion. Here’s a breakdown of how each tool performed.

1. GPTZero: Best Overall AI Detector

GPTZero offers both free and premium versions. The Premium plan ($23.99/month) includes basic and advanced scans. The advanced scan divides long texts into sections and assigns an AI probability score to each.

In my tests, GPTZero flagged some paragraphs with low AI probability (1-5%), but overall it worked well. The cover letter generated by ChatGPT was identified as 100% AI-written, the most accurate detection among the apps. For the mixed human-AI article, GPTZero rated it as 58% human—the closest to reality.

Despite occasional false positives, GPTZero remains a reliable choice for writers interested in spotting AI content.

2. Originality.AI: Accurate but Sometimes Too Generous

Originality.AI costs $12.95/month for 2,000 credits and offers detailed reports. It correctly identified the book chapter as 100% human-written, the only app to do so perfectly.

However, it struggled with AI-generated content designed to avoid detection. The ChatGPT cover letter was rated 91% human, and the half-human article was flagged as fully original with 100% confidence. This suggests Originality.AI can be fooled by text that blends human and AI elements, which is common in practical writing scenarios.

3. Grammarly: Confusing Interface and False Flags

Grammarly’s AI detection is part of its broader writing and plagiarism checks. It costs $30/month if billed monthly. The interface mixes plagiarism and AI detection results, which can be confusing.

Grammarly flagged 7% of the book chapter as matching external sources, a false plagiarism alert. It did not detect AI patterns in that text, which was a relief. However, it failed to catch the AI-generated cover letter and the mixed article, labeling both as fully human.

This inconsistency limits Grammarly’s reliability for writers focused on AI detection.

4. Winston AI: Mixed Results with False Positives

Winston AI, priced at $18/month, offers AI detection but no plagiarism checks unless you upgrade. It rated the book chapter as 96% human, fairly accurate, but flagged some paragraphs incorrectly as fully AI-written.

For the AI cover letter, Winston AI flagged the text as 100% AI but suggested the latter half might be human with a 48% probability. For the half-human article, it correctly reported a 46% human chance but missed some AI sections.

Winston AI shows promise but requires careful interpretation of results.

5. Monica: Least Effective AI Detection

Monica is a multipurpose tool that uses other detection services like Copyleaks and GPTZero for AI detection. It flagged the book chapter as 99% human but gave no detailed feedback.

While it correctly detected the AI cover letter as fully AI-written, Monica failed to identify the AI parts in the mixed article, marking it as 100% human. This major miss limits its usefulness for writers needing accurate AI detection.

Summary for Writers

• GPTZero is the most reliable for detecting AI writing, especially with advanced scans.
• Originality.AI accurately identifies human writing but can miss cleverly disguised AI content.
• Grammarly provides mixed results and false plagiarism warnings, making it less dependable for AI detection.
• Winston AI offers fair detection but can falsely flag human text as AI and vice versa.
• Monica is the least effective and lacks detailed feedback.

For writers who want to stay ahead, it’s useful to understand the strengths and weaknesses of these tools. Detecting AI-generated content is not foolproof yet, but some apps give you a clearer picture than others.

If you want to deepen your skills with AI tools and writing, consider exploring Complete AI Training for courses that cover AI writing and detection strategies.