Retraction checker
Paste a DOI to see whether the paper has been retracted or withdrawn, before you cite it.
The answer will appear here.
A whole bibliography? Use the reference checker.
Questions
Where does the answer come from?
From the publisher's Crossref record. Crossref now maintains the Retraction Watch database, so retractions, withdrawals and expressions of concern are linked to the paper they concern.
Can I still cite a retracted paper?
Only to discuss the retraction itself. Say that it was retracted and cite the retraction notice as well. Never cite it as support for a claim.
I have a whole bibliography to check.
Use the reference checker. It checks up to 20 references at a time for retractions, fabrications and errors.