Similarity Check

For editorial originality, Similarity Check helps editors compare the text of submitted papers for similarity.

Similarity Check is a service for editors who want an extra check. The service helps our members to actively engage in efforts to prevent scholarly and professional plagiarism by providing their editorial teams with access to Turnitin’s powerful text comparison tool, iThenticate. Watch the video below to find out more:

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


With editors under increased pressure to assess higher volumes of manuscript submissions each year, the iThenticate tool provides immediate feedback regarding a manuscript’s similarity to other published academic and general web content. And with a database of over 50 million full-text scholarly content items, editors can be confident that iThenticate will provide a comprehensive and reliable addition to their workflow.

As Similarity Check members contribute their own published content into iThenticate’s database of full-text literature, the service is open to any Crossref member who is actively publishing DOI-assigned article content.


While there are several plagiarism screening tools available, using iThenticate as a Similarity Check member is unique as it creates a symbiotic relationship between content-owners and Turnitin. Similarity Check members enjoy cost-effective use of iThenticate because they contribute their own published content into Turnitin’s database of full-text literature. This means that as the number of Similarity Check members grow, so too does the size of the content database powering iThenticate. More content in the database, means greater peace of mind for editors looking to determine a manuscript’s originality.

Turnitin also provide Similarity Check members with access to additional features in iThenticate, such as enhanced text-matches within the document viewer. And with access to Turnitin’s dedicated Similarity Check support team, our members always have a direct line to Turnitin in order to discuss any iThenticate technical or billing queries.

How it works

In return for a reduced rate of access to iThenticate, Similarity Check members allow Turnitin to index their full catalogue of current and archival published content as this ensures the highest level of text-matching accuracy. This means that the service is only available to members who are actively publishing DOI-assigned content.

Turnitin index members content directly via their Content Intake System. Their CIS accesses our metadata daily to collect the full-text content links provided by our members within their DOI deposit metadata. Turnitin follow these URLs and index the content found at each location. If full-text content is protected by authentication, then the member’s hosting provider must whitelist Turnitin’s IP range to ensure their content is accessible for indexing purposes.

On application to join, members must ensure they have full-text URLs present in at least 90% of their article-level DOI metadata (across all the member’s journal prefixes, if applicable). These URLs need to point directly to the full-text PDF, HTML or plain text content. Member’s must also ensure that these links are included in all future deposits too.

Once member’s meet the eligibility criteria for Similarity Check, Turnitin will provide them with access to iThenticate. Using iThenticate, members will be able to upload their own manuscripts to compare against the full corpus of published academic and general web content in Turnitin’s database. iThenticate provides 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.

How to participate

If you are a Crossref member and are assigning article-level DOIs which include the URL to the full-text PDF, HTML or plain text content, then you are eligible to join Similarity Check. Please follow the steps below to apply:

  1. Review the membership Terms & Conditions on this page and read through Turnitin’s service agreement.
  2. Ensure that you have included full-text URLs in the at least 90% your Crossref article-level DOI deposits and that Turnitin’s IP range will have access to your content.
  3. Complete the online registration form.
  4. Sign a copy of the service agreement and email it back to

Turnitin and Crossref will then review your application and test your DOI metadata to ensure that your content is able to be indexed. Once this is confirmed, you will be able to begin using iThenticate.

For more information about Turnitin’s IP range or for how to include full-text URLs in your DOI metadata, refer to our get started guide. Full technical instructions are available on our help site.

Obligations and fees


Similarity Check fees are in two parts: a per-document checking fee and an annual administrative fee. Per-document checking fees are paid directly to Turnitin and are significantly less than those charged by Turnitin to stand-alone iThenticate users. Additionally, volume discounts also apply. The annual administrative fee is paid to us and is set at 20% of your Crossref annual membership fee.

Terms and conditions

The Similarity Check service is a program being offered by Crossref to its members, on an optional basis. The Similarity Check Service is designed to aid Crossref members in identifying circumstances in which works being considered for publication may have been previously published in whole or in part by (i) facilitating the creation of the Similarity Check Database, (ii) identifying appropriate providers of software tools that can compare the text of works being considered for publication to the text of other works, including those in the Similarity Check Database, and (iii) establishing general recommended terms of participation for Participating Publishers and the identified software provider.

All Crossref members in good standing who currently meet all Crossref member obligations shall be eligible to participate in Similarity Check as “Participating Publishers.” Participating Publishers must make substantially all of their Publisher Content (as further defined below) available for inclusion in the Similarity Check database. To meet the required level of participation, the Participating Publisher must deposit the content associated with at least 90% of that member’s deposited DOIs for full text journal articles, although 100% inclusion of Publisher’s full text content in machine readable form (journal articles, conference proceedings articles, books and books chapters and theses and dissertations) (“the Publisher Content”) is the agreed goal. Components (defined as subparts of content that are generally not citable) and datasets will not be included, and will not be considered “Publisher Content” for purposes of determining the level of participation. This requirement will also apply to the content associated with the Participating Publisher DOI’s deposited monthly with Crossref on an ongoing basis.

In addition, all Participating Publishers will enter into an agreement directly with the plagiarism detection vendor (the “Vendor”) providing the software platform for the Similarity Check services. A form agreement can be found here: Similarity Check Service Agreement


Each Similarity Check Participating Publisher, subject to Vendor’s compliance with the service level standards and reporting obligations contained in the Vendor’s agreement with Similarity Check and in the Vendor’s agreement with each Participating Publisher:

  1. Must make Publisher Content available in the Similarity Check database on an ongoing basis, within no more than 7 days of digital availability, by both registering DOIs for Publisher Content with Crossref within this period and enabling Vendor to index Publisher Content. (Failure of the Vendor to index content made available by a participant will not affect the right of the Participating Publisher to use the Similarity Check service. The Participating Publisher is only responsible for making content available for indexing. Failure to make content available for indexing could result in suspension of the Similarity Check Service for a Participating Publisher.)
  2. Must deposit with Crossref, along with DOIs for the Publisher Content, full, correct and current metadata including article title and all authors.
  3. Must make the full text of the Publisher Content available, as part of the Similarity Check Database, to other Participating Publishers in the context of the interface provided by the Vendor as part of the content checking process. Users of the Vendor’s service who are not Participating Publishers will only see snippets of text with a DOI link to the Participating Publisher’s site, where the Participating Publisher will have full discretion to determine whether and on what terms to user may be given access to the full text.
  4. May not submit works to be checked against the Similarity Check Database through the Vendor’s service until substantially all the journal articles included in the Publisher Content has been made available to the Vendor for inclusion in the Similarity Check database (i.e., >90% of the journal content associated with eligible Participating Publisher DOIs on deposit with Crossref).
  5. Must have full-text URLs (also known as “as-crawled URLs”) on deposit at Crossref that point to the full-text PDF (preferable), HTML or plain text content.
  6. Is responsible for verifying that their in-house and outside editorial staff and reviewers do not use their access to the Similarity Check Service as a “back-door” method for getting free full-text access to included content. The steps to be used to accomplish this should include (i) limiting access to the service to those employees and outside contractors who, in the Participating Publisher’s reasonable judgment, have a need to use the service; (ii) requiring each employee and contractor using the service to register using his or her real name and current job title; (iii) limiting submissions to the service for checking to those that pertain to a publication published by the Participating Publisher; (iv) taking reasonable steps to ensure that account information and passwords used to access the service are kept confidential and are not shared beyond the permitted users of the service; (v) submitting to an audit of users, to be conducted by the Vendor at the Vendor’s cost no more often than once per year, to determine if unauthorized users are being given or are getting access to the Vendor’s services through the Participating Publisher; and (vi) taking reasonable steps to monitor use and potential abuse of the service, based on usage reports to be provided by Vendor.
  7. Shall be entitled to the number of accounts with Vendor that are reasonably necessary for the Participating Publisher to make use of the Service, with no set limit on the number of accounts on a per-member basis.
  8. Shall establish a procedure within the Participating Publisher for help desk and support questions regarding the use of the Vendor’s software, and shall made arrangements for appropriate training for one or more persons including, where feasible, on-site training at the Vendor’s facilities, to facilitate efficient contact between the Participating Publisher and Vendor. The established procedure shall include the designation of a single point of contact with the Participating Publisher unless otherwise agreed in the agreement between the Participating Publisher and Vendor. Such individual agreements may also include additional support and service commitments on the part of the Vendor.
  9. Shall establish a procedure for informing authors that works submitted for publication may be checked through a plagiarism detection system and that, as part of this process, the submitted work will be copied for internal checking purposes and that a copy may be retained, although not further disseminated or integrated into the Similarity Check or other, Vendor supplied databases.

Similarity Check Monitoring and Verification

After an initial start up period of 3 months from the commencement of participation by a particular member, Crossref will have the ability to review the level of participation of Participating Publishers to confirm that they are meeting the obligations of the service. A Participating Publisher who meets those qualifications will have two status indicators available for use. We expect that members will find it valuable to highlight their participation in Similarity Check to demonstrate that they are adding value to the editorial process and cooperating to help ensure that content published as original is properly identified. Suitable logos will be developed that indicate Similarity Check participation, as follows:

“Similarity Check Depositor”: May be displayed on a Participating Publisher’s site and at other locations as set forth in the Similarity Check Trademark Guidelines to indicate that the member has satisfied the requirements for participating in Similarity Check. This will, by implication, indicate that the member is being a “good citizen” in the fight against plagiarism. However, the use of this status indicator does not carry any implication with respect to the plagiarism status of the Participating Publisher’s works.

“Similarity Check Deposited”: May be displayed on articles or other relevant content to indicate that the item has been deposited into the Similarity Check Database. This can act as warning to those who might plagiarize the item.

These phrases and the associated logos will be factual indications that the member participates in the Similarity Check service and that a particular work is included in the database used by the Similarity Check service. Their use does not give any indication or assurances about the content of the particular works with which they are associated, including about whether the particular work contains or does not contain plagiarized materials.

During the period that the initial plagiarism detection vendor, Turnitin LLC., is the sole Vendor for the Similarity Check Service, use of the Similarity Check trademarks and/or logos, as described in these Terms and Conditions, will include the phrase “Powered by iThenticate.”


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 article-level DOIs with us.

What technology are you using to provide this service? We have 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 service agreement with Turnitin to use their system and to provide them with access to your full-text content. This agreement has been fully reviewed and approved by us and several of our members and should not require any additional negotiation.

What is the difference between Similarity Check and iThenticate? Similarity Check is a service specifically for our members. It provides members with cost-effective access to the iThenticate text comparison software from Turnitin. Other organizations and individuals can use the iThenticate service directly by contacting iThenticate.

Similarity Check members benefit from a 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.

I’m not able to include full-text URLs in my DOI metadata. Can Turnitin index my content using another method? No. To ensure the most robust, secure and complete indexing of content, Turnitin is only able to support the direct-indexing method. This involves following the URLs that member’s provide in their Crossref metadata to find and index full-text content. Turnitin do also operate a general web crawler, called Walker, but this crawler targets general web content and is not suitable for comprehensively indexing full-text, published academic content.

Please contact our member services team with any questions or to get set up, or contact our support team for any technical or troubleshooting questions.

For iThenticate user help, please refer to Turnitin’s Similarity Check User Manual or get in touch with their support team at

Last Updated: 2018 May 16 by Madeleine Watson