The following are methods that can be used to help identify the source of a link.
Knowledge Base (KB) Links - KB links will appear above 856 links and DOI links, and they will include Database: [Name of Database] in the description
See: Links from the WorldCat knowledge base to full text content
Links from WorldCat Record 856 field - WorldCat 856 links do not contain Database: [Name of Database] as part of the description.
The screenshots below show an example of checking the MARC 856 field and then hovering over the Access Online link to check the URL is matching from the MARC:
Note: Not all 856 links will surface on a record. When they do you can use the method above to confirm.
See: Links from WorldCat record 856 and 956 to open access content/free content
DOI Links - Will always appear after any KB Links or WorldCat 856 links. They typically fall into one of three categories:
DOI informed by non-WorldCat record 856 field (central index record) - Hover over the Access Online link. Check the MARC 856 field in Discovery by clicking the link next to "Staff View (MARC Record)". If the URL matches, the link is coming from the 856 field.
See: Links from non-WorldCat Record 856
LibKey Links - Mouse Hover over the Access Online button. Check to confirm the URL contains "libkey".
See: LibKey Discovery search results
Unpaywall links - If the DOI link does not match the above scenarios, it is likely from Unpaywall.
See: Open Access DOI links enhanced by Unpaywall
We are finding “Access online” linking buttons to titles that we do not own