The format of bibliographic identifiers in Wikidata is specified via P1793. Constraint violation reports can identify identifiers that don't comply with that pattern, but in the case of very liberal specs (for example the DOI specs, which basically allow any character), the lack of validation can produce nominally well-formed values that don't resolve.

Building on T99046, a bot should be designed to check whether a formatted URL based on an identifier returns a valid resource, or otherwise flag the corresponding statement for review.