Undetectable AI (undetectable.ai) is an AI detection and content rewriting platform that first released in early 2023. It’s best known for its humanizer, which modifies AI-generated text to sound more natural and less detectable by AI scanners. The company even offers refunds if content generated with its tool fails to bypass AI detection.[1]
In addition to the humanizer, Undetectable AI provides various tools for students, teachers, and businesses, including the AI detector featured in this review.
Pros
- Free AI detections with no sign-up.
- Passed 6 of 7 AI detection tests.
- Passed 9 of 10 false-positive tests.
- Free trials and business discounts available.
Cons
- 6 of 8 humanized texts bypassed detection.
- It’s unclear which features each plan includes.
- Annual subscribers receive fewer monthly credits.
Features
- AI detection: Flags AI in text, image, video, or voice.
- Chatbot: Answers questions with human-like responses.
- SEO writer: Generates content designed to rank well online.
- Career tools: Includes a resume generator and AI job applier.
- Writing aids: Grammar checker, word counter, and paraphraser.
- Bulk scan: Looks for AI in multiple URLs or documents at once.
- YouTube transcriber: Creates text from speech in YouTube videos.
- Translator: Supports more than 20 languages.
- Chrome extension
- API
Pricing Plans
Undetectable AI offers three primary plans, each providing access to the same full set of AI tools. The main difference between plans is the number of words (credits) included per month.
| Cheapest | Mid-Price | Most Expensive |
| $19/month or $60/year | $31/month or $114/year | $42/month or $189/year |
| 20,000 words/month or 10,000 if billed annually | 35,000 words/month or 20,000 if billed annually | 50,000 words/month or 35,000 if billed annually |
Basic versions of most tools, including the AI detector, are available to users free of charge.
Undetectable AI also has a business plan with customized pricing and features, non-expiring credits, priority support, access to the smart job applier, and white-label solutions.
Credit Values
AI detection scans are free and can be performed without spending credits. For AI content generation tools (e.g., humanizer, SEO writer), each submitted word counts as 1 credit.
Test #1: Undetectable AI vs. LLMs
The goal of our first test was to assess how accurately Undetectable AI could identify content written entirely by an LLM.
Using the prompt below, we had several LLMs generate 500-word articles. The resulting texts were then scanned with the AI detector to see if the unmodified LLM-generated writing would be flagged as AI.
Prompt Used
“Please compose an article about the RMS Titanic that uses only factual information and is 500 words in length. Write in a natural, human-like style to help avoid AI detection, and do not use em dashes.”
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| LLM | Test Result | Proof |
| ChatGPT – 5.2 Thinking Model | 82% AI
✅ |
 |
| Claude – Sonnet 4.6 Extended | 88% AI
✅ |
 |
| Google Gemini – Thinking | 68% AI
✅ |
 |
| DeepSeek – DeepThink | 86% AI
✅ |
 |
| Perplexity – Free Model | 99% AI
✅ |
 |
| Grok – Auto | 67% AI
✅ |
 |
| Meta | 44% AI
🟡 |
 |
Test #2: Undetectable AI vs. Humanizers
This part of our evaluation involved processing the ChatGPT-generated text from Test #1 through the eight humanizers listed below. Each resulting text was then scanned with Undetectable AI to determine whether the humanized versions would evade detection.
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| AI Humanizer | Test Result | Proof |
| Humanize.ai (humanized text) |
39% AI
🟡 |
 |
| StealthGPT (humanized text) |
22% AI
❌ |
 |
| WriteHuman.ai (humanized text) |
26% AI
❌ |
 |
| SuperHumanizer (humanized text) |
41% AI
🟡 |
 |
| StealthWriter.ai (humanized text) |
40% AI
🟡 |
 |
| WalterWrites.ai (humanized text) |
57% AI
✅ |
 |
| Grammarly (humanized text) |
95% AI
✅ |
 |
| QuillBot (humanized text) |
39% AI
🟡 |
 |
Test #3: False-Positives
For the third and final test, we evaluated whether Undetectable AI would mistake human-written articles for LLM-generated text. To do this, we ran 10 articles through the AI detector and recorded the score assigned to each.
Any instance where human-written content was flagged as AI was treated as a false positive.
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| Article URL | Test Result | Proof |
| The Tell-Tale Heart | 98% Human
✅ |
 |
| For Whom the Bell Tolls (excerpt) | 95% Human
✅ |
 |
| NBC News (article) | 97% Human
✅ |
 |
| Wikipedia (“woodchipper”) | 85% Human
✅ |
 |
| Fox News (article) | 24% Human
❌ |
 |
| Morningstar (article) | 78% Human
✅ |
 |
| Investing.com (article) | 89% Human
✅ |
 |
| Nobelprize.org (interview) | 98% Human
✅ |
 |
| arXiv (academic paper) | 96% Human
✅ |
 |
| Science News Explorers (article) | 83% Human
✅ |
 |
Does Undetectable AI Work?
Test results indicated that Undetectable AI works fairly well at detecting AI and distinguishing LLM-generated text from human-written content. However, it struggled with humanized articles, where its detection accuracy decreased significantly.
Looking at Trustpilot reviews, many customers complained about the pricing and billing system. That said, Undetectable AI still holds an average rating of 3.5 stars.
Frequently Asked Questions
Do unused credits carry over?
It depends. Unused credits do not carry over on standard plans, but they do on business plans.
Are sentence-by-sentence breakdowns provided?
Yes, scanned text is color-coded in detection reports. Content likely generated by AI is highlighted in pink, while text more likely written by humans is highlighted in green (see image).
Is document scanning included?
Yes, users can upload and scan files in TXT, DOCX, PDF, and CSV formats.[2]
Is image scanning provided?
Yes, the AI image detector allows users to scan PDF, JPG, or PNG files up to 10MB in size.[3]
Are user images stored or shared?
No, images uploaded by users are deleted immediately after the detection process.[4]
Are reports shareable?
Yes, AI detection reports can be exported as PDFs and shared with others.
Does Undetectable AI provide certifications?
No, Undetectable AI does not provide certifications proving that a scan occurred or that content is guaranteed to be AI-free.
Are AI detections used for internal training?
Nothing in Undetectable AI’s privacy policy or terms of service indicates that AI detection results are used to train its AI models.