These days, we’re all aware of plagiarism and don’t want to do it or appear to do it. However, there are some not-so-obvious ways you can plagiarize:

• Re-using some of your own previous writing. Yes, self-plagiarism is a thing, and you will get pinged for it. That’s why it’s best to re-write every time rather than modify something that applies to a new paper.
• Using direct quotes without proper citation. Really in STEM, it’s best not to use direct quotes from other work at all. Summarize from a paper you read, don’t quote it.
• Using an AI tool to help you write. AI tools can be useful for helping you spot grammar issues and helping you get “unstuck”, but be careful not to rely on them too heavily, not only because you need to demonstrate your own knowledge and abilities but also because they do plagiarize inputs to a certain degree.
• Sometimes our brains can copy phrasing sort-of subconsciously, so that you end up with a sentence or paragraph that is highly similar to something you read without meaning to be.

Being questioned on the originality of your work sounds like zero fun, so aside from following best practices, it can be useful to use a “plagiarism checker” to be sure ahead of your deadlines. Chances are that your University uses Turnitin or a similar tool to make sure that your work isn’t plagiarized when you submit it. Turnitin is a powerful, subscription-based tool that gives a similarity score between your paper and sources it can find on the internet.

Luckily, I found some free tools you can use on your own before you submit. To test their accuracy and utility, I prepared a plagiarized document (~2 pages single-spaced, 993 words) of copied and pasted text from 3 academic publications and a blog article on my own website. One of the academic publications was open source and two were closed access/behind a “pay wall” (requiring payment for access). They were published in Nature (closed access, impact factor for that year: 41.5), Science of the Total Environment (closed access, impact factor: 10.8), and Biogeochemistry (open access, impact factor: 4.8).

I then ran this page on each of the top free tools. Here’s a description of the tools and how they fared:

• Grammarly, known more for checking your grammar and spelling, also has a plagiarism checker. It only gives you a check mark or not, and it gave me a check mark. It failed to catch any of my copy-and-paste text from either academic publications or from my own website.
• EasyBib is another well-known tool for students that turns out to also offer a plagiarism checker. Annoyingly, it made me sign up before trying it out, and unfortunately, the free version also only gives a yes or no answer. It did find something in my test but I’m not sure how much, as it declared only “We found plagiarism errors in your paper.”
• Scribbr’s checker, powered by Turnitin, claims to be the “most accurate” checker of 2022. This also made me sign up before trying it out, and it requires an upload rather than providing a text box to paste into. The free version gives a simple level of risk output, with a premium version offered to give you a percentage score. With the free version, will show you a blurry “report” on matches it finds, with only the website name and number of words that are similar clear to see. From that limited info, Scribbr seems to have found the Nature publication text, but failed to catch anything else. It gave me the score “high risk of plagiarism.” Oddly on my first test, which contained only 2 academic publications, it actually failed to catch that too and gave me a “low risk of plagiarism” score. I had hypothesized that it might be due to the pay wall, so I added an open access publication to my text. However, in this new test, it didn’t find the open access source, and instead suddenly found the Nature paper.
• Dupli Checker gives you a percentage score similar to what Turnitin outputs, so that’s more useful. Also useful, if it does find plagiarized work, it will show you the source. It fared better than the previous two in spotting academic text, but still didn’t catch every sentence – only a bit from each of the three publications. It didn’t find my website. It gave me a score of 35% Plagiarism, 65% Unique.
• Plagiarism Detector is similar to Dupli Checker in how it works, with a percentage score and sources. It found more, but not all, of the text from academic publications. It also didn’t find my website. It gave me a score of 48% Plagiarized, 53% Unique.
• Small SEO Tools’ plagiarism checker only allows up to 1000 words without going premium, so its best use would be for abstracts and short assignments or for a blog post. Like Dupli Checker and Plagiarism Detector, it found some of each of the academic publication texts. It added some stats about the text and gave me a score of 30% Plagiarized, 70% Unique.
• Que Text was the first one to catch my self-plagiarism from my own website. However, it failed to find any of the academic sources. I also found out that after a free trial run, the free version only lets you check 1 page of up to 500 words per month. The score it gave me was 34% of “text that matches text elsewhere.”
• CopyLeaks caught my website text, the Nature paper, and the open-access Biogeochemistry paper, just not the Science of the Total Environment paper. The score was thus a 72.9% match, with added metrics of results found, a similar word count, and what percentage were identical, minor changes, paraphrased, or omitted words. It also showed the sources, but locked all but two, only to be seen if I signed up. Unfortunately, it seems only the first ten are free though.
• PlagiarismChecker.co fared best out of all of the checkers I tried. It limited my word count to 800 so I had to remove a couple paragraphs, but it found all of my plagiarized sources, including my website. It didn’t match every sentence though. It gave the score 73% Plagiarism, 27% Unique, and provided the sources and additional metrics about the document, with a downloadable report. (The featured image of this post is from my test report).
• Other tools that ended up finding my website but not academic text include the plagiarism checkers on PapersOwl and A Research Guide, which both gave me a score of 35.2% similar, 64.8% original/unique.

Based on this little experiment, I found that no plagiarism checker is perfect, but PlagiarismChecker.co and CopyLeaks are both likely to give you a good idea of what issues (if any) you might need to address in your work. I’ve included links to each of the tools tested below. With that, good luck and happy writing!