To verify that a knowledge base link will work as an 856 link for a corresponding MARC record, test the link in the WorldShare interface. The link labeled "Website" under the "Identifiers" column for the title is used as the 856 link. If clicking this link resolves to the resource, it will work correctly as an 856 link.
Please note that for links to work correctly, the corresponding knowledge base settings must be configured. For proxied access to resources, this means providing the proxy URL prefix in Settings. Some providers also require additional identifiers to create links to full-text. These can be supplied in the "Provider Settings" accordion of the Settings. For a complete explanation of knowledge base settings, see Institution settings.