SSL Checker
Error
Valid Certificate Invalid / Expired
Subject (Owner) Details
| Common Name (CN) | |
| Organization (O) | |
| Organizational Unit (OU) |
Issuer (CA) Details
| Common Name (CN) | |
| Organization (O) | |
| Organizational Unit (OU) |
Certificate Validity
| Valid From | |
| Valid To | |
| Serial Number |
Properties & Constraints
| Basic Constraints | |
| Key Usage | |
| Extended Key Usage |
Subject Alternative Names (SANs)
An SSL certificate quietly expiring is one of those problems that goes from invisible to embarrassing overnight, one day the site works fine, the next every visitor gets a browser warning. This tool checks a domain's certificate status, chain and expiry date on demand, so you can catch a lapsing certificate before your visitors do.
Ensure your website is secure by testing your SSL certificate status, chain, and authority details instantly.
Keep track of expiry dates and renewal schedules to avoid critical browser security warnings for your visitors.
Verify cryptographic parameters, signature algorithms, key sizes, and subject alternative name (SAN) configurations.
What gets checked
- Certificate validity and current status
- Expiry date and remaining time before renewal is needed
- Issuing certificate authority
- Signature algorithm and key details (commonly SHA-256 with RSA or ECDSA on modern sites)
- Subject Alternative Names (SANs) covering additional domains or subdomains
A common error worth knowing about
A "domain mismatch" happens when the domain you're visiting isn't listed in the certificate's Common Name or SANs, often after adding a new subdomain without reissuing the certificate to cover it. The fix is straightforward: reissue the certificate with every domain and subdomain it needs to cover included. Most commercial certificates run for a year, while free options like Let's Encrypt renew every 90 days, so it's worth checking on a schedule rather than waiting for a browser warning to remind you.
Checking a server's overall security posture? An Open Ports Lookup is a natural next step alongside this.
FAQS
What is an SSL certificate?
An SSL (Secure Sockets Layer) certificate is a digital certificate that authenticates a website's identity and enables an encrypted connection between the web server and a user's browser, keeping sensitive data secure.
Why is it important to check my SSL status?
Regularly checking your SSL status helps ensure your certificate is valid, matches your domain, and hasn't expired. An expired or mismatched certificate displays security warnings to visitors, leading to lost traffic and trust.
How do I fix a "Domain Mismatch" error?
A domain mismatch occurs when the domain name you are visiting is not listed in the certificate's Common Name (CN) or Subject Alternative Names (SANs). You can resolve this by re-issuing the certificate to include all necessary domains.
What does the Signature Algorithm mean?
The Signature Algorithm determines the cryptographic hash functions and encryption methods used by the Certificate Authority to sign the certificate. Modern secure websites typically use SHA-256 with RSA or ECDSA encryption.
What are Subject Alternative Names (SANs)?
SANs are an extension in SSL certificates that allow you to secure multiple domain names, subdomains, or IP addresses under a single certificate instead of purchasing separate ones.
How often do SSL certificates need renewal?
Most commercial SSL certificates are valid for 1 year, while free certificates (like Let's Encrypt) are valid for 90 days. It is highly recommended to set up auto-renewal to prevent service disruption.