Inspect any domain's SSL/TLS certificate in real time: issuer, validity dates, Subject Alternative Names (SANs), full certificate chain, key algorithm, and Certificate Transparency log history - all in one query.
An SSL lookup inspects the SSL/TLS certificate served by a domain - returning issuer details, validity dates, Subject Alternative Names (SANs), full certificate chain, key algorithm, and TLS version. It also surfaces Certificate Transparency log entries showing every certificate ever issued for the domain pattern.
How is SSL Lookup different from checking a certificate in my browser?
Browsers show basic certificate details for the page you're currently viewing. SSL Lookup queries any domain remotely without visiting it, returns the certificate chain in full structured form, parses the complete SAN list, and cross-references Certificate Transparency logs - none of which a browser surfaces conveniently.
What are SANs (Subject Alternative Names) and why do they matter?
The SAN field of an SSL certificate lists every hostname the certificate is valid for. A single certificate often covers a primary domain plus dozens of subdomains, related domains, and CDN endpoints. For OSINT and security research, SAN fields are one of the most reliable ways to discover undocumented subdomains and related infrastructure.
What are Certificate Transparency (CT) logs?
Certificate Transparency logs are public, append-only records of every SSL certificate issued by trusted Certificate Authorities. Every legitimate CA must publish issued certificates to CT logs. Monitoring CT logs for newly-issued certificates matching your brand keywords is one of the earliest signals of an impending phishing campaign or impersonation attempt.
What does it mean when a certificate is "about to expire"?
SSL certificates have a fixed validity period - typically 90 days for Let's Encrypt, 1 year for commercial CAs. Browsers begin showing warnings 30 days before expiry; expired certificates cause HTTPS failures, broken page loads, and SEO penalties. Monitor critical certificates so renewals happen before expiry.
How do I look up SSL certificates for multiple domains at once?
For bulk SSL certificate inspection across a portfolio, use the SSL Certificate API, which supports concurrent requests and scheduled re-checks for expiry monitoring at scale.
Can I look up SSL certificates for subdomains?
Yes. Enter any subdomain (e.g., shop.example.com) to check its specific certificate. Alternatively, a wildcard certificate (*.example.com) covers all direct subdomains - SSL Lookup will show the wildcard coverage in the SAN field.
Common Name*.onlineszamla.nav.gov.huOrganizationNemzeti Ad\C3\B3- \C3\A9s V\C3\A1mhivatalLocality/CityBudapestCountryHU
Certificate Issuer
Common Namee-Szigno OV TLS CA 2023OrganizationMicrosec Ltd.Locality/CityBudapestCountryHU
Public Key
Size256 bitAlgorithmECDSA
PEM:
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE7IlOjM0zTJkiuWlfJilgztFCMTiFxwLn+hDoKQBVBnO8MLyo9u2j105ygkJeucxl2VWQEq3+wna4EzTaxCtgoQ==
-----END PUBLIC KEY-----
