The factorable.net site provides
key checker to
verify whether weak or compromised key or not.
However this can only check X.509 certificate or SSH public key.
Thus you can't easily check your key before its certificate issuance
by PKCS#10 CSR (certificate signing request) or PKCS#8 PEM public key.
This tool can generate a fake certificate by specifying CSR
for checking factorable weak key checker.
Resulting certificate has wrong signature value but it doesn't matter for the checker.