SSL Certificate Checker (Expiry & Issuer Lookup)
Enter a domain name to check its SSL/TLS certificate's expiry date, issuer, SAN, and fingerprint. Days remaining are color-coded so you never miss a renewal and risk site downtime.
Tips
- Check expiry dates well ahead of time. Renewing 2-4 weeks before expiry gives you a buffer in case the renewal process runs into trouble.
- Free certificates from Let's Encrypt and similar CAs only last 90 days, so it's worth checking here periodically that your auto-renewal is actually working.
- The browser padlock icon only tells you whether a certificate is currently valid — it never shows how many days are left, which is exactly the gap this tool fills.
- The SAN (Subject Alternative Names) field can list several hostnames beyond the main domain, such as a www subdomain. It's worth checking that no unexpected domains are included.
- The fingerprint uniquely identifies a certificate. Comparing fingerprints before and after a renewal is a reliable way to confirm the swap actually happened.
Frequently asked questions
Side Note — A brief history of SSL/TLS certificates and certificate authorities
The HTTPS connections we rely on every day trace back to SSL (Secure Sockets Layer), developed by Netscape in 1994. Early SSL 2.0 had serious vulnerabilities, and after SSL 3.0 the protocol was standardized as TLS (Transport Layer Security) 1.0 in 1999. The name changed, but the core design — encrypting traffic using certificate-based public-key cryptography — has carried through to today.
Certificate authorities (CAs) verify that an applicant genuinely controls a domain before issuing a signed certificate. Obtaining a certificate used to cost money and take real effort, but that changed dramatically in 2016 when the nonprofit ISRG launched Let's Encrypt, a free CA. Its certificates are only valid for 90 days, though, which effectively requires automated renewal tooling such as certbot in any real deployment.
An expired certificate is more than a scary browser warning — it can escalate into a serious outage. There have been repeated, well-publicized incidents of major API services and even large financial institutions going down for hours because a certificate renewal was missed, which is why ongoing monitoring remains an operational necessity rather than a one-time setup task.