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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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Information for Libraries

Created: ; Last Update: December 18, 2019.

Estimated reading time: 5 minutes

LinkOut provides direct links from PubMed and other NCBI databases to a wide range of information and services beyond the NCBI systems. LinkOut aims to facilitate access to relevant online resources to extend, clarify, and supplement information found in NCBI databases. LinkOut resources include full-text publications, biological databases, consumer health information, research tools, and more (see examples of LinkOut resources).

How LinkOut Works for Libraries

LinkOut allows participating libraries to link directly from PubMed citations to their library’s link resolver where library full text resources and Interlibrary Loan options are available to their users. Libraries icons and links to their link resolver display in all PubMed citations.

LinkOut does not perform any user verification. Once a user clicks on a link for a local link resolver, access depends on pre-existing licensing agreements between the library and the full-text provider(s).

PubMed and OpenURL-based Services

Section contents:

About PubMed & OpenURL-based Services

OpenURL is a syntax for packaging metadata and identifiers describing information objects and for pointing to a user-specific appropriate copy of the object. The syntax has been accepted as a NISO standard.

PubMed supports OpenURL-based services through Outside Tool. Outside Tool allows libraries to place a link to their OpenURL-based service on all PubMed records.

Implementing OpenURL-based Services in PubMed

OpenURL-based services can be registered with NCBI to provide a link from the Abstract display of PubMed records. This link points back to a service offered by the institution for their local users.Your library’s OpenURL-based service can be implemented as an Outside Tool.

Outside Tool does not differentiate between online holdings, print holdings, or items that will have to be ordered from another institution. Outside Tool does not allow users to limit a search to library holdings or to display library holdings as a filter in the search result.

Evaluating Your OpenURL-based Service

To implement an OpenURL-based service through Outside Tool, we require the service to provide functional links to the following qualified resources from each PubMed record. This requirement allows us to best serve our user community, by avoiding "blind" links that do not provide useful and specific information for the individual PubMed record.

Qualified resources are:

  • Full-text: The link should lead directly to the article level for the online full text, not the table of contents or the journal homepage.
  • Library holdings via the local OPAC: The link should lead directly to the OPAC Holdings display or to the corresponding bibliographic record with holdings/location information displayed. The link should not lead to a general catalog or search page.
  • Local document delivery service: The link should produce a form with citation information already populated for the user. This is a requirement for Outside tool implementation.

Due to the scope of PubMed, it is unlikely that any single library will be able to provide electronic holdings for every citation in PubMed. A link to a local ILL service must be available to provide users a means to obtain the full text for citations the library does not hold.

In order to best serve all users and expedite processing, libraries requesting Outside Tool must provide a unique base URL that identifies their link resolver. Outside Tool requests that list a base URL already registered will not be assigned a new Outside Tool account. Instead, the existing link resolver with the same base URL should be used.

To determine whether your OpenURL-based service meets the qualifications for implementation as an Outside Tool, construct a URL to your service and retrieve the PubMed records listed below.

To construct the URL to your OpenURL-based service, combine the base URL of your service with a PMID:

Base URL: https://baseURL/OpenURL_local
Tail: ?sid=Entrez:PubMed&id=pmid:
PMID: 12345678
Resulting URL: https://baseURL/OpenURL_local?sid=Entrez:PubMed&id=pmid:12345678

Please test all of the following PMIDs to verify that your service is working correctly. Your service MUST provide one qualified resource for each PMID tested.

PMIDs for testing








All resources must be in place before the registration request is submitted. If your local service cannot provide one qualified resource for each PMID tested, it cannot be implemented as an Outside Tool.

If your service can provide one qualified resource for each sample PMID, it may be implemented in PubMed as an Outside Tool. Proceed with the registration process described in Outside Tool: Register Your Service.

Activating Library Icons in PubMed

Library icons may be activated in PubMed: through a special URL to access PubMed, by using a shared My NCBI account, or by signing in to My NCBI.

Displaying Library Icons through a special URL to access PubMed

To display Outside Tool icons through a simple link to PubMed, use the following URL:

For the new PubMed use:

Replace Outside Tool with the Outside Tool username assigned by NCBI.

Displaying Library Icons using a shared My NCBI account

My NCBI accounts can be configured so that database filter selections, Outside Tool selections, and highlighting selections can be shared by multiple users. Outside Tool icons can be selected in My NCBI and activated using a special URL. To do this, please follow the instructions in the Sharing My NCBI Account Settings section of this manual.

Displaying Library Icons in My NCBI

Library icons can be selected in My NCBI and displayed while the user is signed in to their My NCBI account. See PubMed Preferences – Outside Tool.

To display icons without signing into My NCBI, set up a Sharing My NCBI Account Settings for your patrons.

Localizing PubMed for Your Users

In addition to displaying library icons in PubMed, there are a variety of ways to “localize” the PubMed display, allowing users to link directly from PubMed to library services and other resources. This section provides information on:

About Cookies and Special URLs

Many of the features used to create a localized PubMed environment use “special URLs”. When a user enters PubMed through a special URL, a cookie is placed in the workstation that instructs PubMed to set the preferences indicated by the URL. To use special URLs, the workstation must be able to accept cookies.

Cookies will expire after 8 hours of inactivity. At this time, the PubMed options will be reset to the default settings. To reactivate your preferences, the user must enter PubMed through the special URL again. You can set preferences that will not time out on a workstation by signing the workstation in to My NCBI and selecting Keep me signed in.

Sharing My NCBI Account Settings

My NCBI accounts can be configured so that Filter selections, Outside Tool, and highlighting selections can be shared by multiple users.

To share account settings:


Register for a My NCBI account that will be used to share settings with patrons. Libraries should use their LinkOut User Name as the My NCBI account User Name.


Sign in to the account and click NCBI Site Preferences to select the services you want for your library’s My NCBI account. Under PubMed Preferences:


To select Filters, click PubMed Filters and Icons. On the resulting page search for your library and click the check boxes under the column “Filter.”


To select an Outside Tool, click Outside Tool. On the next page, select the radio button next to the desired library and click “Save”


To select highlighting preferences, click the link Highlighting under Common Preferences. Select the radio button next to the desired color and click “Save”


To select which services to share click the links NCBI Site Preferences and click the Shared Settings link under Common Preferences. On the resulting page, click the check boxes for the settings you would like to share. Only the settings for a service where the Share Selection box is checked will be shared.

After selecting the features you want to share, use the following special URL to activate the settings:


For the new PubMed use:

Advanced Search:

Replace username with the shared My NCBI account Username.

Settings activated using a shared My NCBI account URL will time out after 8 hours of inactivity.

Clearing Settings Using a Special URL

To clear LinkOut settings activated using a special URL and return to the default PubMed display, access PubMed using the following URLs:

To clear the Outside Tool icon:

For the new PubMed use:

To clear the myncbishare setting:

For the new PubMed use:

In the above URLs, there are two underscores ( _ ) preceding reset.


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