SSL Checker

Certificate expiry is the leading cause of self-inflicted HTTPS outages: teams buy, install, and forget their certificates until a browser warning is already greeting visitors. The SSL Checker inspects the TLS certificate served on port 443 of any hostname and surfaces everything a fast review requires, the negotiated protocol and cipher suite, subject and issuer details including organization and country, the exact validity window, and, most usefully, a days-remaining figure color-coded green, amber, or red as the deadline closes in. A valid-or-invalid badge summarizes whether the certificate chain authorizes the hostname you asked about, while the serial number, SHA fingerprint, and full subject-alternative-name list give you the details needed to compare against an issuance record or debug a name-mismatch warning. Entering a hostname with or without the https:// scheme works, and every check times out after fifteen seconds so a dead host does not hang the page. Whether you are a site owner setting a renewal reminder, a QA engineer verifying a new deployment, or a curious visitor validating a shopping site, this TLS certificate checker turns what was once an OpenSSL command-line chore into a one-click inspection.

1. 1

   Type a bare hostname such as example.com into the Hostname field; the https:// prefix and any path are stripped automatically.

2. 2

   Press the Check certificate button, or hit Enter inside the field, to query port 443 on that host.

3. 3

   Read the Valid or Invalid badge, then the Days remaining, Protocol, and Authorized stats in the result header.

4. 4

   Compare the Subject and Issuer rows side by side to confirm who the certificate was issued to and by whom.

5. 5

   Inspect Valid from and Valid to, the serial number and fingerprint, then scan the Subject Alternative Names list for the domains you expect.

• Confirming a client site's certificate is still valid before launch day instead of discovering expiry in production.
• Verifying that a shared-hosting certificate actually covers all of your subdomains via the SAN list.
• Double-checking the issuer and organization after switching certificate authorities.
• Spotting name-mismatch problems when users report browser warnings for www versus apex domains.
• Adding an expiry check to a manual pre-deployment checklist when no monitoring is configured.
• Teaching HTTPS basics by comparing valid, expired, and self-signed certificates side by side.

• Schedule a recurring check at least 30 days before expiry; the days-remaining stat turns amber under 30 and red under 7.
• Verify the SAN list contains every hostname you serve, including the www variant, because browsers fail closed on mismatches.
• Do not judge security by the padlock alone; confirm the issuer is a CA you recognize and the certificate is not self-signed.
• Keep an eye on the negotiated protocol: TLSv1.2 minimum is table stakes, and TLSv1.3 should be your target.
• Renew before the amber window whenever possible, since CA processing delays can easily consume a 30-day buffer.
• Treat an Invalid result on your own domain as an incident; visitors may already be seeing interstitial warnings.

• Enter the bare domain without https://; the tool strips schemes and paths, but the hostname regex rejects spaces and IP addresses.
• Keep a list of your domains and re-run this tool monthly as a poor-man's certificate monitor.
• Compare the fingerprint before and after renewal to confirm the new certificate is actually being served.
• When SANs look incomplete, check your load balancer or CDN, which sometimes terminate TLS with their own certificates.