SSL Certificate Checker
Check the TLS certificate a public HTTPS host is serving on port 443, including expiry, issuer, subject and SAN coverage.
The certificate lookup uses NetworkCalc's public Security Tools API. The domain and request metadata are sent to that third-party service.
What this checks
The lookup reads the TLS certificate served by the requested public host at check time. It can confirm the certificate subject, issuer, validity dates and Subject Alternative Names. It does not prove the website itself is trustworthy or malware-free.
How to interpret the important fields
The validity window tells you when the certificate becomes valid and when it expires. The issuer identifies the certificate authority or issuing chain name reported by the lookup. Subject Alternative Names (SANs) list hostnames the certificate is intended to cover. If you are checking www.example.com, that hostname should be represented by the certificate directly or by an appropriate wildcard such as *.example.com.
A certificate can be valid by date and still be wrong for the hostname, while a hostname can be covered correctly by a certificate that is close to expiry. That is why expiry, subject/SAN coverage and the actual host being checked should be reviewed together.
Expiry status
NexusNova calculates days remaining from the certificate's reported valid_to timestamp. Expired and not-yet-valid certificates are clearly flagged rather than treated as healthy. If a certificate is near expiry, check the hosting or certificate-management system responsible for renewal instead of assuming a browser cache will fix it.
A practical troubleshooting example
If a browser shows a certificate warning after a DNS or hosting change, first confirm the domain resolves where you expect with DNS Lookup, then run this checker for the exact hostname. If the served certificate lists a different hostname or old validity period, the server, proxy or CDN may still be presenting the wrong certificate. If the certificate looks correct here but the browser still warns, compare the browser's certificate details and local clock before escalating.
Why port 443 only?
The underlying service can inspect other ports, but this public browser tool deliberately stays on standard HTTPS port 443 to keep its scope narrow and reduce abuse. It also rejects localhost, private-address forms and internal-style hostnames.
What this tool does not verify
This page does not perform a full vulnerability scan, malware check, application-security review or private-network inspection. A valid certificate only shows that a TLS identity credential is being served for the checked host; it is not a guarantee that the website or organization behind it is safe.
Certificate validity is one part of HTTPS health
A TLS certificate binds a public key to names and a validity period. Certificate metadata can help reveal subject names, issuer and expiration information seen for a public HTTPS endpoint, which is useful when investigating an unexpected certificate or a renewal date.
A valid certificate is not a guarantee that the application is secure or healthy. Certificate chains, hostname matching, server configuration, protocol support, authentication and application controls also affect the real service.
Pair certificate checks with service context
Confirm the hostname you tested is the hostname users reach, then compare the certificate details with the server or provider configuration. For an outage, use DNS and application diagnostics alongside this result.
Use certificate details to narrow a problem
A TLS certificate helps a browser verify a website hostname and establish encrypted HTTPS communication. Compare the expiry date, issuer and subject alternative names with the hostname entered. A certificate may cover one hostname but not another, and different servers can serve different certificates.
For example, a certificate that lists example.com may not cover shop.example.com unless the second name or a suitable wildcard is included. If the expiry date is approaching, the site operator should check the renewal and deployment chain. If the certificate looks valid but a browser still reports a warning, investigate the hostname, intermediate chain, client clock, proxy and the exact error message.
Interpretation and limits
This check targets the public HTTPS service on port 443 from the checker’s network vantage point. It does not test every route, private hostname, custom port, certificate chain seen by every browser, application login or the security of the site's content. A successful certificate check is one useful signal, not a full website security audit. Do not send credentials to a page merely because its certificate is valid.
Certificate-checking questions
Does a valid certificate mean a website is trustworthy?
No. It helps secure the connection to the hostname but does not certify the owner’s intentions, content quality or business legitimacy.