The Crossref Curriculum

Similarity Check

A service provided by Crossref and powered by iThenticate—Similarity Check provides editors with a user-friendly tool to help detect plagiarism.

Our Similarity Check service helps Crossref members prevent scholarly and professional plagiarism by providing immediate feedback regarding a manuscript’s similarity to other published academic and general web content, through reduced-rate access to the iThenticate text comparison software from Turnitin.

Only Similarity Check members benefit from this tailored iThenticate experience 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.

Watch the introductory Similarity Check animation in your language: français; español; português do Brasil; 简体中文; 日本語; 한국어; العربية; bahasa Indonesia; or English below.


With editors under increased pressure to assess higher volumes of manuscript submissions each year, it’s important to find a fast, cost-effective solution that can be embedded into your publishing workflows. Similarity Check allows editors to upload a paper, and instantly produces a report highlighting potential matches and indicating if and how the paper overlaps with other work. This report enables editors to assess the originality of the work before they publish it, providing confidence for publishers and authors, and evidence of trust for readers. And as the iThenticate database contains over 50 million full-text scholarly content items, editors can be confident that Similarity Check will provide a comprehensive and reliable addition to their workflow.

Making sure only original research is published provides:

  • peace of mind for publishers and authors that their content is identified and protected,
  • a way for editors to educate their authors and ensure the reputation of their publication, and
  • clarity for readers around who produced the work.

Benefits of Similarity Check

Similarity Check participants enjoy use of iThenticate at reduced cost because they contribute their own published content into Turnitin’s database of full-text literature. This means that as the number of participants grows, so too does the size of the database powering the service. More content in the database means greater peace of mind for editors looking to determine a manuscript’s originality.

Crossref has worked closely with Turnitin to ensure iThenticate is enhanced to meet the specific needs of our members, providing extra features such as enhanced text-matches within the document viewer.

How the Similarity Check service works

To participate in Similarity Check, you need to be a member. Similarity Check subscribers allow Turnitin to index their full catalogue of current and archival published content into the iThenticate database. This means that the service is only available to members who are actively publishing DOI-assigned content and including in their metadata full-text URLs specifically for Similarity Check.

Turnitin indexes members’ content directly via its Content Intake System (CIS). Its CIS accesses our metadata daily to collect the full-text content links provided by our members within their metadata. Turnitin follows these URLs and indexes the content found at each location.

When you apply for the Similarity Check service, Turnitin will check that they can access your existing content via the full-text URLs in your Crossref metadata. Once confirmed, you’ll be provided with access to the iThenticate tool where you will be able to submit manuscripts to compare against the corpus of published academic and general web content in Turnitin’s database. You can do this in the iThenticate tool, or through your manuscript submission system using an API. iThenticate provides a Similarity Report containing a Similarity Score and a highlighted set of matches to similar text. Editors can then further review matches in order to make their own decision regarding a manuscript’s originality.

Fees for Similarity Check

Similarity Check fees are in two parts: an annual service fee, and a per-document checking fee.

The annual service fee is 20% of your Crossref annual membership fee and is included in the renewal invoices you receive each January. When you first join Similarity Check, you’ll receive a prorated invoice for the remainder of that calendar year.

Per-document checking fees are also paid annually in January. Volume discounts apply, and your first 100 documents are free of charge.

Similarity Check infographic

Download the Similarity Check factsheet, and explore factsheets for other Crossref services and in different languages.

How to participate in Similarity Check

Similarity Check is only available to Crossref members. If you aren’t yet a Crossref member, then you can apply to join.

As a Crossref member, when you apply to join the Similarity Check service, you must ensure you have full-text URLs present in the metadata of at least 90% of your registered articles (across all your journal prefixes). These URLs must point directly to the full-text PDF, HTML, or plain text content. You must also include these links in all future deposits too. If you aren’t registering any journal articles and instead are registering other content types (such as conference papers), please contact us.

Please note that the metadata you deposit with Crossref is available to be searched and retrieved by everyone, and this includes Similarity Check URLs. If your content is paywalled, please make sure that your Similarity Check URLs prompt an authentication step before allowing a user to access full-text content. You’ll also need to ensure that your hosting provider has whitelisted the Turnitin IP range to ensure that the content is available for them to index.

You can check the percentage of Similarity Check URLs already included in your metadata using the widget below - just start typing your account name in the box, select the correct one from the list, and your result will be automatically calculated. Don’t worry, you don’t need to know your Member ID.

If you do meet the threshold, the widget will link you to a form where you can apply for Similarity Check and click to accept the service terms. If you don’t meet the threshold, the widget will provide a .csv file to download which shows all your DOIs that don’t have the links. It will also provide instructions for how to add the missing full-text URLs.

Member Name
Member ID
Good news - you’re eligible to register for our Similarity Check service.

You can now apply here and accept the service terms.

Once we receive your application, we’ll work with the team at Turnitin to confirm that they can access your content. We’ll also send you a pro-rated invoice for your first year subscription to the service. Don’t forget, if your full-text content is protected by authentication, then you’ll need to ask your hosting provider to whitelist Turnitin’s IP range to ensure your content is accessible for indexing purposes. Do make sure that this is done before you apply.

We’re sorry, but you are not eligible to register for our Similarity Check service just yet.
To be eligible you need to register full-text urls for Similarity Check pointing to the full text article for more than 90% of your content. Find out how to add these full-text urls for Similarity Check to your existing content. To see exactly which content items are missing the full text article, simply click the “Generate CSV” button above. Please note, this CSV can only show the first 10k content items. If you have more than 10k content items missing DOIs, please contact us on and we'll be able to provide you with the full list.
We’re sorry, but you are not eligible to register for our Similarity Check service just yet.
It looks as though you haven’t registered any content with us yet. To be eligible for Similarity Check you need to be registering content with us and including URLs for Similarity Check that point to the full text article for at least 90% of your content. Find out more about how to register content and learn more about full-text URLs for Similarity Check.

Please note - if you aren’t registering ANY journal articles at all and are only registering non-journal content (eg conference papers, books) then the tool may not give accurate results. Please get in touch with our membership team for more help.

Last Updated: 2020 April 8 by Amanda Bartell