How Accurate Is Copyleaks AI Detector? We Tested It Against GPTZero and ZeroGPT

From my opinion, a good AI detector should do more than identify text that was generated entirely by AI.

Pure AI-generated content is usually the easiest was to detect. however, whether a detector can distinguish between the following three senarios is the key factor for a true accurate detector:

1. Text generated entirely by AI

2. AI-generated text that has been substantially edited by a human

3. Text written entirely by a human

Because AI detector is easy to detect "100% human" or "100% AI", but mixed human can be tricky to detect.

This article tests whether Copyleaks can make those distinctions.

I tested each sample with Copyleaks, GPTZero, and ZeroGPT.

I focused mainly on one question:

Can these detectors accurately reflect how much human involvement was present in the final text?

By comparing the results before and after human editing, we can see whether Copyleaks provides a accurate detection, or simply classifies content as either AI or human.

Quick Answer: How Accurate Is Copyleaks?

Based on our test, Copyleaks was accurate.

It classified the pure AI generated text as 100% AI. After the article was partially edited by human, the AI score is still 100%. For the purely human written article, Copyleaks report it as human written.

Here is a quick overview of the results:

Copyleaks accurately detected the unmodified sample of AI content, and reported a lower AI score for the heavily edited sample of human writing. Copyleaks also reported the closest AI score to the ground truth for the sample written purely in human language, making it the most accurate detector in this test.

How We Conducted the Test

To make the comparison as fair as possible, we kept the three samples similar in topic, format, and length.

The first article was 100% AI written and not edited.

The second article was 100% AI written, but also massively rewritten by a person. The editor took the structure, rewrote the sentences, added original details, and chopped out generic content.

The third article was manually written from a blank page and not containing any AI written sentence or an AI generated outline.

For each detector, we recorded:

● The overall result

● The displayed AI score

● Highlighted AI sentences

Test 1: Completely AI-Generated Content

For the first test, I asked [ChatGPT] to write an article about [The Impact of AI on Education].

The article contained approximately [150] words.

We copied the result directly into Copyleaks, GPTZero, and ZeroGPT without making any changes.

Original AI-generated sample

Here is a short excerpt from the original article:

Artificial intelligence has the potential to improve education, but it should support teachers rather than replace them. AI tools can provide students with immediate feedback, personalized exercises, and explanations that match their level of understanding. This can be especially useful in large classes, where teachers may not have enough time to help every student individually. However, relying too heavily on AI may reduce students’ ability to think independently and solve problems without assistance. AI systems can also provide inaccurate or biased information, which students may accept without checking. For this reason, schools should teach students how to use AI critically and responsibly. Teachers should remain responsible for evaluating student progress, explaining complex ideas, and encouraging discussion. When used with clear rules and human supervision, AI can make learning more accessible and efficient. Nevertheless, it should be treated as an educational tool, not as a substitute for human judgment, creativity, or meaningful interaction.

Below is the tested results from Copyleaks, GPTZero, ZeroGPT:

Copyleaks reprted it as 100% AI:

GPTZero reported it as 100% AI:

Zerogpt reported it as 100% AI:

Pure AI detection results

All three dectector are coorected, they all reported it as 100% AI.

Test 2: Partially AI-Generated Content

For the first test, I asked [ChatGPT] to write an article about [The Impact of AI on Education], and then I rewrited half of these paragraph to see what will happen.

Rewritten AI-generated sample

Artificial intelligence has the chance to improve education, but it should help teachers rather than replace them. AI tools can provide students with personalized and immediate feedback, , and explanations that match their understanding. This can be extremely useful in large classes, where teachers may not have enough time to help every studentto improve. However, relying too heavily on AI may reduce students’ ability to think independently and problem solving skills. AI systems can also provide inaccurate or biased information, which students may accept without further checking. For this reason, schools should teach students how to use AI critically and responsibly. Teachers should remain responsible for evaluating student progress, explaining complex ideas, and encouraging discussion. When used with clear rules and human supervision, AI can make learning more accessible and efficient. Nevertheless, it should be treated as an educational tool, not as a substitute for human judgment, creativity, or meaningful interaction.

Below is the tested results from Copyleaks, GPTZero, ZeroGPT:

Copyleaks reprted it as 100% AI:

GPTZero reported it as 100% AI:

Zerogpt reported it as 53% AI:

AI detection results

Copyleaks and GPTZero still report it as 100% AI, while ZeroGPT report it as 53%, which is more accurate.

Test 3: Completely Human-Written Content

For this test, I asked rewritten all the paragraph by myself, and see what the dtecttion results will be

Rewritten AI-generated sample

Artificial intelligence can play a role in education but it should help teachers, not replace them In large classes, AI systems can provide feedback, explanations and adaptations that match each student's knowledge and can mine the content to give precisely the knowledge needed to advance. This is of considerable value as a teacher and learning aid but overuse could interfere with independent thinking and problem solving, as AI systems can produce incorrect or biased information that students may take for granted Nonetheless teachers need to assess student progress periodically and explain complex ideas and maintain discussions To take the full benefit of AI, schools need to teach students how to use it critically Human-centred learning will have a vital role to play to complement the benefitsJust like with any critically useful tool, when guided with boundaries AI can contribute to effective learning but cannot replace human interaction, education and judgementWe must therefore try to use AI as a teacher's aid, not a teacher's alternative.

Below is the tested results from Copyleaks, GPTZero, ZeroGPT:

Copyleaks reprted it as 0% AI:

GPTZero reported it as 0% AI:

ZeroGPT reported it as 0% AI:

AI detection results

All three detector report it as human written this time, they are all correct.

Final Comparison

All three detectors correctly identified the two clear cases: the completely AI-generated paragraph and the completely human-written paragraph.

The main difference appeared in the partially human-edited sample.

Copyleaks and GPTZero did exactly the same thing in all three tests. They perfectly identified the pure AI and pure human samples, and both returned the partially edited sample as 100% AI.

ZeroGPT was better on the combined sample. Its 53% AI was much closer to reality, since roughly half the original paragraph had been rewritten by a real person.

Final Verdict: How Accurate Is Copyleaks?

According to the test, Copyleaks did the right thing when it had a text that was decidedly AI- or human-generated.

The company was wrong in its assessment of the partially cleaned-up paragraph: Even though half of the paragraph had been rewritten by a human, Copyleaks still marked it as 100 percent AI.

Copyleaks is good at distinguishing between pure AI versus pure human but - in this case - struggled with the mixed bag text. ZeroGPT had the most accurate assessment for the mixed bag.

In this test (bullet points):

●Copyleaks correctly flagged purely AI content.

●Copyleaks correctly flagged purely human content.

●Copyleaks incorrectly flagged partially computer edited content as 100 percent AI.

●ZeroGPT flagged the partially computer edited content relatively accurately.

Copyleaks was correct in two of the three tests. But here is the point of this (philosophically) in the acceptance of AI text detectors: AI scores are a gauge, and not a gospel.