Merlin AI Detector Review 2025: Can It Really Spot AI Text?

If you’ve been using AI to write or edit your work, you’ve probably wondered how good tools like Merlin AI Detector really are at spotting it. Can it actually tell if your text was written by AI or not? 

In this review, we’ll break down how Merlin performs in different tests, what it gets right (and wrong), and whether it’s worth using before you submit your work. 

Let’s find out.

What Is Merlin 

Merlin AI is an AI productivity assistant available as a free Chrome extension. 

It combines the power of ChatGPT with a variety of AI writing and analysis tools, helping students and content creators generate, summarize, and check content all in one place.

What Is Merlin AI Detector

Merlin AI detector is a tool that identifies whether a piece of text is AI-generated. It works by analyzing linguistic patterns, sentence structures, and other “fingerprints” left by AI models like ChatGPT, GPT-4, or Google Gemini. 

The detector uses two main techniques: perplexity and burstiness. 

Perplexity measures how predictable each word is, with lower values often indicating robotic phrasing. 

Burstiness tracks sentence variation, since humans naturally mix short and long sentences, while AI tends to produce uniform lengths. 

Additional signals like token distribution, syntax variety, and vocabulary richness further refine the analysis.

Merlin AI detector supports multiple formats—you can paste text, upload documents, or use the API. It’s context-aware and works across 128+ languages, giving instant results even on large files. For clarity, it highlights AI-suspect sentences and can generate detailed PDF reports. 

Extra Tools in Merlin

The platform includes over 26 AI tools to enhance writing and research. Some notable features are:

• Plagiarism checker – ensures content originality

• AI Chat – interact with AI for research or idea generation

• Essay Writer – draft essays or summaries quickly

• Image and AI content generators – from illustrations to literature reviews

• Sentence and paragraph rewriters – improve style or humanize AI-generated text

How Accurate Is Merlin AI Detector

Merlin AI detector claims it can reliably spot AI-generated text, but how well does it really work? 

To find out, I ran a series of tests using different types of content: fully AI-written text, a mix of human and AI writing, and AI text that’s been humanized by tools like QuillBot. 

Here’s a look at how it performed.

Test 1: Pure AI Text

Setup: 

To create this test, I generated a full paragraph using ChatGPT-5. This gave me 100% AI content to see if Merlin could detect it.

Results: 

Merlin labeled the text as 100% AI-generated.

Observations: 

This result was expected and reassuring. It shows that Merlin can reliably spot text written entirely by AI. 

The tool seems particularly sensitive to patterns like uniform sentence lengths and predictable word choices—classic signs of AI writing.

Test 2: Mixed AI + Human Writing

Setup: 

For this test, I took a paragraph written by a human before ChatGPT was released and then asked ChatGPT-5 to continue it. 

The final text had 187 human-written words (41%) out of 454 total words, creating a mix of human and AI writing.

Results: 

Merlin reported 51% AI-generated.

Observations: 

This score feels realistic. It reflects the mixed nature of the text, identifying roughly half as AI while recognizing the human portions. 

Merlin seems to balance signals like sentence structure variation and word choice to detect partial AI content.

Test 3: Humanized AI Text by QuillBot

Setup: 

Here, I took the 100% AI text from Test 1 and ran it through QuillBot’s advanced AI Humanizer mode to make it read more human-like.

Results: 

Surprisingly, Merlin still flagged it as 100% AI-generated.

Observations: 

This shows that Merlin can detect AI text even after humanization tools try to disguise it. While QuillBot changes sentence phrasing and style, Merlin picks up on the underlying linguistic patterns that remain AI-like.

Pros and Cons of Merlin AI

Pros

• High Accuracy: Merlin reliably detects AI-generated content, especially from popular models like GPT-3 and GPT-4.

• Fast and Easy to Use: The simple interface delivers results almost instantly, making it ideal for quick checks.

• Multilingual Support: Supports over 128 languages, making it versatile for global content.

• Detailed Reports: Confidence scores and PDF reports provide clear insights into detection results.

Cons

• File Upload Limits: Free users have lower upload limits, while the Pro version allows up to 50MB—important for long documents or batch checks.

• Cost: Some advanced features require a paid plan, which may not fit all budgets.

Merlin Pricing

Merlin offers both free and paid plans to suit different levels of AI use. 

Free Plan

The free plan lets you test the AI Detector on up to 3,000 words per check and gives limited access to basic AI models, over 70 AI tools, basic image generation, Chrome extension features, and device syncing.

Pro Plan

For heavier or more frequent use, the Pro plan costs $19 per month and removes word limits for AI detection. It also unlocks advanced models like GPT-5 and Claude Sonnet 4.5, unlimited access to all 70+ AI tools, advanced image generation, batch uploads, extended Chrome extension features, and priority support.

Can You Bypass Merlin AI Detector

The short answer? Not easily. 

Simple tricks like swapping words or lightly rewriting sentences can slightly lower an AI score, but they usually aren’t enough. 

In Test 3, for instance, we ran 100% AI text through QuillBot’s advanced humanizer, and Merlin still flagged it as 100% AI-generated. 

To reliably stay below detection—generally under 20% AI—you need a professional humanization tool.

EssayDone Humanizer is one such tool, designed to make AI-generated content read like it was written by a real person. It restructures sentences, varies syntax, and adjusts word choice to mimic natural human writing patterns.

The results are impressive. Using the 100% AI text from Test 1, EssayDone lowered the AI detection score to just 4%, effectively turning fully AI-generated content into something virtually indistinguishable from human writing. 

By targeting both linguistic patterns and sentence structure, professional humanizers like EssayDone offer a reliable way to create content that reads naturally while passing AI checks.

Alternatives to Merlin AI Detector

FAQ

Is Merlin 100% accurate?

No — nothing is. Merlin is strong at spotting obvious AI patterns (especially older, widely-used models), but it can give false positives or miss heavily edited text. Treat its score as a signal, not an absolute verdict.

How to bypass Merlin AI detector?

Simple word swaps or paraphrasing tools often fail to fool Merlin. In our tests, even QuillBot’s advanced mode couldn’t lower the AI score. For reliable results, you’d need a professional humanizer that rewrites structure and tone naturally.

Will my professor use an AI detector?

Possibly. Many instructors and institutions now use AI and plagiarism tools, especially in large classes or writing-heavy courses. If you’re unsure, ask your professor or check your course policy.

Can I use AI detectors on my own work before submission?

Yes — and it’s a smart move. Running your drafts through detectors can highlight passages that still look machine-like and help you fix wording or add original analysis before you turn things in.

Are AI detectors legal?

Yes — using AI detectors is legal. However, how schools use results can involve academic policies and privacy rules, so consequences vary by institution. Always follow your school’s conduct and data-use policies.

Is the Merlin AI detector free?

Merlin offers a free plan (good for light use) and a Pro plan. The free tier allows limited checks (around 3,000 words per check), while Pro removes many limits and unlocks advanced models and features.

Conclusion

So, that wraps up our look at the Merlin AI Detector. 

It’s clear that while the tool performs fairly well in catching AI-generated text, it’s not flawless—detection limits still happen.

Hopefully, this review helped you understand what to expect from Merlin and how it compares to other detectors out there. 

Anyway, knowing how these tools work can help you write smarter and spot AI use more confidently.