DupliChecker.com, Quetext.com, Plagium.com and PaperRater.com are all free web-based plagiarism detectors. Viper and Plagiarism Checker X are free software applications for detecting plagiarism. Many free versions of plagiarism checkers require users to register for an account. Others limit the features that are available.
Quetext offers unlimited plagiarism searches without the requirement of registering for an account. However, there is no option to upload text files, so users must copy and paste all text into the web-based search box.
The free version of Plagium allows users to search documents of up to 5,000 words at a time, but payment is required to use the uploading function and the features included with the free version are limited.
Paper Rater offers plagiarism detection in conjunction with spelling and grammar checking. A premium account is required for documents longer than 5,000 words, and for uploading documents.
Viper is available to Microsoft Windows users, and checks documents against 10 billion sources online, according to the company's website. The software is completely free; there are no upgrades available.
Plagiarism Checker X is also available for Microsoft Windows, and can scan documents in a variety of formats including doc, PDF, rtf and plain text. The program offers three different types of reports that vary in the amount of detail they give about the scanned document.