Mozilla TLS Observatory
FreeDeprecatedNot yet verified
Scans a domain's TLS setup and X.509 certificate chain and grades it against Mozilla's guidelines.
Example request
curl -A 'WildAPIsResearch/0.1 (+https://wildapis.com)' 'https://tls-observatory.services.mozilla.com/api/v1/certificate?id=1'
Free tier, in plain English
No key or account required; the only stated limit is one rescan per target every 3 minutes.