The MediaWiki API should be able to be given a sample input string and return whether the string would be a valid title. For example, the string "abc" would return True while the string "aB{" would return False (as "{" isn't allowed in page titles).
This would essentially be a dry-run mode of action=edit, but would allow for some sanity checks when, for example, testing whether strings are valid template parameter names.
Optionally, this test could check against other restrictions such as the local title and global blacklists or the AbuseFilter to see if a specific string matches (though this possibly opens up an attack vector).
Version: unspecified
Severity: enhancement