The following are methods that can be used to help identify the source of a link.
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.
DOI Links - Will always appear after any KB Links or 856 links. They typically fall into 1 of 3 buckets:
The example screenshots below are of a DOI informed by 856 field. They 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
LibKey Links - Mouse Hover over the Access Online button. Check to confirm the URL contains "libkey"
Unpaywall links- If the DOI link does not match the above scenarios, it is likely from Unpaywall.
How can I tell if a link is from the WorldCat Knowledge Base or is a DOI link?