There are a few tools and resources available that can help you check if an article is retracted. Retraction Watch has information on retractions as well as a searchable database. Many library provided resources, i.e. ProQuest databases, will list RETRACTED in the article's title. The journal's website will post a RETRACTION NOTICE. Both libkey nomad and JETfind now have retracted article information.
As of August 2023, there was an update to JETfind to include information on retracted notices and retracted publications. Please note that this feature is not 100% and other resources, such as Retraction Watch or the Journal's website, should also be consulted. This information will show up in two different ways.
Retracted Publication and/or Retraction Notice tag in the article's information.
Retracted Publications and/or Retractions Notices options under Resource Type.
JET Library also uses a feature from Libkey to facilitate direct linking (labeled as Download PDF), this can also display Retracted Article information and it is a separate feature from the one described above.