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LinkOut Help [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2006-.

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LinkOut Help [Internet].

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Related Services: Outside Tool

Created: ; Last Update: June 21, 2023.

Estimated reading time: 4 minutes

The Library Outside Tool service places a link to a link resolver on every PubMed citation.

Section contents


Outside Tool allows a library to place a link on every PubMed record. This link points back to a link resolver offered by the institution for their users. Only one Outside Tool can be set up for each link resolver software unique base URL.

To best serve users, NCBI tries to avoid “blind” links that do not provide useful and directly relevant information for the specific PubMed record. Therefore, to register an Outside Tool, an institution must demonstrate that their link resolver software can provide relevant Web-accessible resources for all PubMed records.

Examples of relevant resources include:

  • online full text
  • library holdings via the local OPAC
  • local document delivery service (ILL form with prepopulated citation metadata is a requirement)

Search forms, tables of contents, journal home pages, bibliography building software, and other such resources that are not directly relevant to the PubMed record do not qualify as relevant resources.

All resources must be implemented locally before a request to set up an Outside Tool can be processed.

How It Works

PubMed links to your service by attaching the PubMed ID (PMID) of the current PubMed citation to the end of the URL of your link resolver base URL. For example:

Your tool URL: http://goodmedical.edu/mytool.cgi?
PMID: 12345678

Resulting URL: http://goodmedical.edu/mytool.cgi?12345678

Please note that PubMed will only pass back the PMID. Your software would then use E-Utilities to obtain citation information.

You can test your link resolver by constructing URLs as described above.

Register Your Outside Tool Service

Library LinkOut accounts are only issued to libraries. The Outside Tool service is not available for trial purposes.

Library link resolver software should be in place before a registration request is submitted. For your Outside Tool registration, you must provide:


The base URL of your link resolver software in the following format https:​//yourbaseURL?sid​=Entrez:PubMed&id=pmid: Note that the base URL should be unique to your institution. For example:


Four test URLs (i.e., 2 for full-text and 2 for ordering) including PMIDs to demonstrate the links resolve to the
actual resource/full-text or to a pre-filled order form. Provide requested test URLs in the following format:

Full-text https://goodlibrary.linkresolver.com/openurl?sid=Entrez:PubMed&id=pmid:20639561 
Pre-filled ILL form https://goodlibrary.linkresolver.com/openurl?sid=Entrez:PubMed&id=pmid:12345678

We will conduct further testing based on your 4 samples.

3. If access to full-text or the ILL/order form is password-protected, provide a temporary username and password that NLM staff can use to conduct testing. No requests will be sent.

4. The name, postal address, and phone number of the library/institution.

5. The name and e-mail address of the contact persons. Optional: A second email address for a group, e.g., librarystaff@university.edu.

6. A file (.png, .gif, or .jpeg) of an icon that will identify your institution in PubMed. For icon specifications and examples of
icons, see LinkOut Technical Information - Icons. If you are unable to provide a file, please provide a URL for the icon. The icon
URL must lead to a publicly available site.

7. The URL of a web page from your library/institution that explains your institution’s full-text service (not your vendor’s), to be included in the My NCBI directory of Outside Tool services.

8. A short label (under 50 characters) that will identify your institution and local service in My NCBI. Outside Tool services are listed alphabetically, therefore, begin your label the with your institution name. NCBI reserves the right to edit this label.

9. If your institution is already using LinkOut, please provide that Name Abbr (username)

Fill out the Library LinkOut Help Desk form with the subject line: “Request to set up an Outside Tool.” In the text of the message, use the following numbered format based on the explanations above:

Subject: Request to set up an Outside Tool


Base URL of your local service


Test URLs. Must include test URL to ILL service with citation prepopulated form


Temporary Username and Password for password-protected access


Institution name, postal address and phone number


Contact person name and e-mail address. Optional group e-mail address


URL of the Outside Tool icon to be displayed in PubMed


URL of your institution Help page


Short label that identifies your


If your institution has a LinkOut account, please provide the Library LinkOut username

Manage Your Outside Tool

After initial implementation of Outside Tool, libraries can manage their Outside Tool accounts through the Outside Tool Account Settings. See the Outside Tool Account Settings chapter of this manual. Please note that any changes to the Outside Tool settings or icon takes 48 hours to be implemented.

In the Outside Tool Account Settings libraries can edit:

  • Outside Tool contact(s) information
  • Tool Settings (Outside Tool label, base URL, help page URL and allow listing in MyNCBI)
  • Outside Tool icon

In addition, Outside Tool users can access statistics recorded by clicking “View Usage Statistics.” Statistics are kept for the last 12 months.

Display Your Outside Tool Icons in PubMed

Once your Outside Tool has been implemented, users can activate your Tool in two ways, by accessing PubMed through a special URL or by using My NCBI.

Display Your Outside Tool Icons Using a Special URL

To display your Outside Tool icon, append otool=username to the PubMed URL and enter PubMed through the resulting URL:


Replace username with the Outside Tool Username assigned by NCBI.

Appending otool=username to the PubMed URL displays your Outside Tool icons in PubMed’s Abstract display. Users click on your library’s icon to access your link resolver landing page.

Create a button or link to this URL from your library website. Replace your current PubMed links (in your catalog, on subject pages, etc.) with this URL and send a general announcement so that other departments in your institution can update their websites and personal computers.

When a user enters PubMed through a special URL, a “cookie” is placed in the workstation (more about cookies). This cookie instructs PubMed to display your Outside Tool icons. To use Outside Tool, the workstation must be able to accept cookies.

The cookie will expire after 8 hours of inactivity. To reactivate your icons, the user must enter PubMed through the special URL again.

Display Your Outside Tool Icons Using My NCBI

To activate your Outside Tool using My NCBI, users should:

  • Sign in to My NCBI (more about My NCBI).
  • Click the link NCBI Site Preferences, and then click Outside Tool under PubMed Preferences.
  • Select a library from the list of Outside Tool services available


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