Top 20 free Online Plagiarism Checkers

15 mins read

I have been an avid CopyScape user for a couple of years. Lately, I have been having my doubts on whether CopyScape might be the best plagiarism checker considering there are very many free online plagiarism checkers nowadays and it does not have to cost you an arm and a leg to avoid plagiarism.

Plagiarism can be very costly to you as a web publisher or as a freelance writer. Contrary to what most bloggers might tell you, your site’s rankings will drop once you start posting duplicate content.

As a freelancer, clients often refuse to publish and subsequently pay for work that has traces of plagiarism. This can be very discouraging especially if you find that it was from an important client.

As a student, plagiarism is one of the worst forms of academic indiscipline. It is usually severely punished and it is not uncommon to find students who were expelled because of plagiarism.

Plagiarism can be easily avoided by using both free and premium online plagiarism checkers to scan documents and posts for duplicate content before publishing.

How to Avoid Plagiarism

The best way of evading plagiarism as a writer is to avoid borrowing too much content from the original sources. Sometimes in the process of researching and writing, it becomes harder to forge new content from the sources especially if you are unfamiliar with the topic.

Paraphrase and Summarize

These are two of the most indispensable tools in research. Mastering these two tools will make online plagiarism checkers obsolete for you. Paraphrase and summary allow you to include other people’s ideas in your work without plagiarizing. Consider relying on either tool when an idea from one of your sources is important to your research but the wording is not.

Above all, think about how much of the detail from your source is relevant to your argument. If all your reader needs to know is the bare bones, then summarize. Ultimately, be sure not to rely too heavily on either paraphrase or summary. Your ideas are what matter most.

The paraphrase must be entirely in your own words. You must do more than merely substitute phrases here and there. You must also completely alter the sentence structure. As a writer this is the only guaranteed means of avoiding plagiarism. However, it is very difficult to find new words to describe an idea that was already perfectly expressed by the original author.

There are a few strategies that can help you to get around this common problem.

  1. During the research process when you come across a piece of text that you feel would be useful in your writing, it is important to avoid copying the words verbatim (word for word). Spend a few minutes reading through the text. Close the window, open your text editor and attempt to write all the main pieces of information from the research material. This will make it easier to craft your own words.
  2. If you think you will want to paraphrase the passage, make a note only of the author’s basic point. You don’t even need to use full sentences.
  3. Avoid using passive voice to paraphrase.

With these strategies you will be able to produce plagiarism free work. Sometimes plagiarism can appear in your work, and it is always adviseable to check all content using plagiarism checkers before publishing.

Example of a proper paraphrase

Text from “An Anthropologist on Mars”

The cause of autism has also been a matter of dispute. Its incidence is about one in a thousand, and it occurs throughout the world, its features remarkably consistent even in extremely different cultures. It is often not recognized in the first year of life, but tends to become obvious in the second or third year. Though Asperger regarded it as a biological defect of affective contact — innate, inborn,analogous to a physical or intellectual defect — Kanner tended to view it as a psychogenic disorder.

Paraphrased text

In “An Anthropologist on Mars,” Sacks lists some of the known facts about autism. We know, for example, that the condition occurs in roughly one out of every thousand children. We also know that the characteristics of autism do not vary from one culture to the next. And we know that the condition is difficult to diagnose until the child has entered its second or third year of life. As Sacks points out, often a child who goes on to develop autism will still appear perfectly normal at the age of one. Sacks observes, however, that researchers have had a hard time agreeing on the causes of autism. He sketches the diametrically opposed positions of Asperger and Kanner. On the one hand, Asperger saw the condition as representing a constitutional defect in the child’s ability to make meaningful emotional contact with the external world. On the other hand, Kanner regarded autism as a consequence of harmful childrearing practices.

Free Plagiarism Checkers

I decide to test out as many plagiarism checkers as I could find online. I soon found out that there are very many free and premium plagiarism checker sites online, but very few live up to their promise.

For the purpose of this comparison I dug around my PC and I found content that I had written, but was still unpublished. I copied some random content from the internet into my unpublished articles. To be precise they were 150 words, spread out across 5 plagiarized sentences, all plagiarized from different websites. This means that a perfect (there isn’t one) plagiarism checker should be able to detect about 25% plagiarism. A reliable plagiarism checker should detect around or close to 15% of the text as being plagiarized.

I first ran a plagiarism check of the text using CopyScape, and it only detected 9% plagiarism. This is rather disappointing. So how did the free plagiarism checkers hold up?

I picked the top 20 and listed them for you to try out.

Plagiarisma uses a freemium business model. With a free/unlimited membership you are limited to only 10 and 100 daily searches respectively. Plagiarisma offers a plagiarism checker, url checker, a very good article rewriter, and a similarity checker (for side by side comparison). For students, teachers, and academic writers the site also includes a grammar checker, scholar (checks journals and databases) and a books search. To make your work easier they have desktop software, browser extensions for Firefox and chrome.

Plagiarisma was surprisingly accurate, maybe too accurate in my case. Not only did it detect all the 6 plagiarized sentences plus their sources, it also flagged other parts of my article that weren’t plagiarized.

Duplichecker is free, with some limits on daily searches and number of words. The site also provides very many other useful SEO tools such as a metatag analyzer, whois checker, broken link check, keyword density, page speed, pinging tool, and so many other tools I should probably write another post to cover all of them.

Duplichecker, surprisingly, produced very similar results to CopyScape. I had to check with other articles, and all the results were still 100% similar. Damn, duplichecker is in fact a free version of CopyScape.

  • Viper – Detected 13% plagiarism

Viper works entirely through desktop software, and there have been some complaints of the software being spyware. The plagiarism checker is mainly developed and optimized for students and academic essays. It comes bundled with many features such as side by side comparison, local-database check, and links to the source of plagiarism.

Nonetheless, according to the site’s TOS, they will upload/sell the papers after three months. According to some sources they upload all your papers to their site within a month. I would not advise you to use viper.

Plagium offers everything that CopyScape serves. This includes url check, plagiarism check, and an alert service that is similar to Copysentry, albeit with a freemium model. The plagiarism checker is free although it is limited to only 10 daily checks (you can always get around this limit by clearing your cookies).

Paperrater basically edits your paper for grammatical, punctuation, and many other English writing errors. Additionally, the website also offers a free and unlimited plagiarism checker. It is a great tool for students. The plagiarism checker was surprisingly accurate.

The site has a very simple and easy to use UI. There are no limits and you can upload ms word documents 0r copy paste the text. Surprisingly it also produced very similar results to CopyScape and duplichecker. My favorite copyscape alternative. The premium version produces better and more accurate results.

Very easy to use. This plagiarism checker tool requires no registration, has no limits and it is pretty fast. You can copy and paste text, or upload .docx documents. Also detected same level of plagiarism as CopyScape.

The rest on the list only barely worked or even failed to work completely. Give them a try to see if they will work for you.

Best Plagiarism Checkers for Academic Work

Plagiarism checks for academic work are slightly different. Most of the plagiarism checkers out there such as Copyscape are made for web content. This makes them insufficient for checking for plagiarism in academic papers, because in academic work the sources used for most of the research are journals as opposed to web pages. All major academic publishing companies such as Elsevier and Ebscohost place all their journals behind a paywall. Access to any journal article requires an expensive subscription.

This also means that very few plagiarism checkers can be able to check for duplicate content from academic journals.

WriteCheck is the best for checking for academic plagiarism, but it is a bit too pricey. Some free alternatives that work include Plagtracker and Plagscan.

Initially, I planned on writing this article as a way of proving the inferiority of the free plagiarism checkers because I couldn’t imagine that any of them could be as good as CopyScape. I was surprised to come across duplichecker, and plagscan which seem like perfect alternatives of CopyScape yet they are free. Plagiarisma was also a surprising free alternative which in fact surpasses all the plagiarism checkers that I have come across yet it is free. I think I might have to abandon CopyScape for one of these alternatives.

Which Plagiarism checker do you use, and how effective is it?



I am a web developer most of the time. I enjoy writing about online work, business, travel, and technology.


  1. I really loved that one, since it’s full of interesting facts
    and it is a kind of article. I spent just a couple of minutes reading,
    and because of well-structured text, then I know it totally.

  2. I appreciate yur great info. Tried getting all these thru social media BT pple r unwilling to give yu the info yu need. Thanx a lot. I’m expecting to receive those ebooks to familiarize myself with academic writing

  3. I’ve used most of mentioned tools, but I’ve found great one for me, which has also free version – It’s both payed and free, but still very accurate, so you can choose the best option for you and your needs. I think it’s awesome alternative to CopyScape as well.

  4. Hello Sammy Kikwai,

    Thank you for the great feedback. However, I do not agree about the Noplag. I would like to ask you, what exactly didn’t work on This is great, easy to use, with free checks – plagiarism detection service. I would be happy to give you a walk through to proof that it works and that it is a great alternative to CopyScape as well as Turnitin.

    Let me know a good time so we can schedule a webinar where I will show you how it works and how accurate results it produces.


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