Similarity Check faqs

Do I need to be a Crossref member to join Similarity Check?

Yes, the Similarity Check service is only available to members who are depositing DOIs with Crossref.

What technology are you using to provide this service?

Crossref has partnered with leading plagiarism screening systems vendor Turnitin to create the Similarity Check database and to use their iThenticate tool for checking documents against the database. As a Similarity Check member you will need to sign a license with Turnitin to use their system; this license has been fully reviewed and approved by Crossref and several of its member publishers and should not require any additional negotiation.

What is the difference between Similarity Check and iThenticate?

Similarity Check is a plagiarism screening service that uses the iThenticate text comparison software from Turnitin.  Similarity Check is a service for scholarly and professional publishers, and publishers must join Crossref or be an existing Crossref member to participate.  Other organizations and individuals can use the iThenticate service directly.

Similarity Check members benefit from a tailored service that includes read-only access to the full text of articles in the Similarity Check database for comparison purposes, discounted checking fees and unlimited user accounts per organization.  Similarity Check participants also benefit from membership of the Similarity Check community of publishers and are encouraged to display Similarity Check logos to show their participation in the project and deter potential plagiarists.

Authors and researchers can pre-screen manuscripts or dissertations using iThenticate to ensure that they have attributed all sources and are not inadvertently misappropriating content. This is a separate service to Similarity Check and is optional, but can help to ensure that sources are correctly cited ahead of submission  Visit to learn more.  

How will my content be indexed?

Your content will be crawled in much the same way that a search engine would index your full text, but rather than crawling your entire site the Similarity Check crawler uses a site map of deposited DOIs to locate content and start crawling at your DOI landing page, or directly at the full text if you have registered "as-crawled" URLs with Crossref. Upon arrival at the DOI landing page the crawler needs to be redirected to full text. Further information on how to do this can be found on the Similarity Check Indexing page.

How do I check a document for possible plagiarism?

To check a document for possible plagiarism you simply upload the document using the web-based iThenticate tool and choose whether to check it against just the Similarity Check database, or additionally iThenticate's database of other proprietary content and/or the open web. The system will then produce a "similarity report". This report shows the percent of the document that matches other content in the database, where that content comes from, and the matching content itself; information that a human can then use to make a judgement on whether there has in fact been a case of plagiarism. Uploading a document to iThenticate does not add the document to the Similarity Check database, and you can delete the document from the system upon completion of the similarity screening.

An Similarity Check user manual (PDF 3.6 MB) is also available to download.

What do I do if I find a case of possible plagiarism?

Each organization is likely to have their own protocols and procedures for dealing with misconduct, but there are also several other resources available. See our list of useful resources and guidelines.

What is the definition of a "document"?

Documents submitted for checking are defined to be article or chapter length works of no more than 50 pages. (Note: documents submitted for checking do not get stored or included in the database and can be deleted after checking via the iThenticate interface).

How does Similarity Check work with manuscript tracking systems?

Manuscript tracking vendors are encouraged to integrate Similarity Check into their manuscript tracking systems in a way that is flexible enough for the publishers to use Similarity Check where they see fit in their editorial process. Crossref is currently meeting with manuscript tracking vendors to discuss how to best integrate Similarity Check. A comprehensive API guide is available, or vendors can contact

What do researchers and scholars need to know about Similarity Check?

Please see this page for more information on how plagiarism screening helps researchers.

Sign up for Similarity Check updates.

Updated May 4, 2016

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