The SSL Certificate Checker is an online tool for checking the SSL/TLS certificate status of a website or server. Enter a domain or IP address and an HTTPS port, and the tool attempts to establish an SSL/TLS connection and parse the X.509 digital certificate returned by the server. This helps you quickly determine whether the certificate is valid, when it expires, and which certificate authority issued it.
After the check is completed, you can view the server IP address, check time, elapsed time, and detailed SSL certificate information, including certificate status, remaining days, valid-from date, expiration date, subject, issuer, certificate version, serial number, signature algorithm, and public key type.
The tool displays the certificate valid-from date, expiration date, and remaining validity days. These details help identify HTTPS certificates that are approaching expiration and reduce the risk of browser security warnings, HTTPS access failures, or API connection errors caused by expired certificates.
The certificate subject describes information such as the domain name and organization associated with the certificate. The issuer identifies the certificate authority (CA) that signed and issued the certificate. Checking these fields helps confirm which certificate is currently deployed on the server and where it came from.
Website SSL/TLS certificates commonly use the X.509 format. The check can parse the certificate version, serial number, signature algorithm, public key algorithm, and public key length, providing useful information for certificate troubleshooting and HTTPS configuration checks.
www.example.com.443.SSL certificates have a defined validity period. After a certificate expires, clients will normally consider the HTTPS connection untrusted. For websites, APIs, payment systems, and other services that depend on HTTPS, certificate expiration can directly affect user access and secure communication between systems.
If the remaining validity period is short, confirm the renewal or reissuance plan and complete certificate updates on the server, load balancer, CDN, or reverse proxy before expiration. For production environments, it is recommended to establish certificate expiration monitoring instead of waiting until a certificate has already expired.
HTTPS is built on HTTP and TLS. During the TLS handshake, the server normally provides a digital certificate to the client. The client uses the certificate validity period, trust chain, hostname matching, and signatures to determine whether the server identity and secure connection can be trusted. Therefore, the SSL certificate is an important component of an HTTPS connection.
SSL certificate checking focuses mainly on the actual digital certificate returned by the server and its X.509 information, such as validity, issuer, signature algorithm, and public key. SSL security scoring may additionally evaluate TLS protocol versions, cipher suites, HTTP security headers, certificate chains, and server security configuration. The two checks therefore have different scopes.
A certificate being within its validity period does not mean that the entire HTTPS configuration is correct. You should also check whether the hostname matches the certificate, whether the certificate chain is complete, whether TLS is configured correctly, and whether the page contains HTTP mixed content.
If a website uses a CDN, load balancer, or multiple servers, different network nodes may use different certificates. When DNS resolution changes, the SSL connection may reach a different server, so the detected server IP and certificate information may differ.
SSL certificates are normally issued for domain names rather than directly for public IP addresses. When a TLS connection is established through an IP address, the server may return a certificate for a domain based on SNI, so the certificate subject may display a domain name.
A result showing “Certificate Valid” means that the certificate obtained from the current SSL/TLS connection is within its validity period at the time of the check. Remaining days indicate how long remains before expiration. Subject and issuer identify the service and certificate authority, while the signature algorithm and public key information describe the cryptographic parameters used by the certificate.
This tool is suitable for website operators, server administrators, developers, and security professionals who need to quickly check HTTPS certificate status. The result reflects the certificate actually returned by the server at the time of testing. When a server uses a CDN, load balancer, or multiple nodes, it is recommended to perform checks from the relevant user network environments.
Comments 0