How does the SSL checker test a certificate?

Enter a hostname (example.com) and the tool opens a TLS connection, fetches the full certificate chain, and reports issuer, subject, validity dates, SANs, signature algorithm and chain trust. It also checks HSTS headers and looks up the cert in Certificate Transparency logs to spot misissuance. You see exactly what a browser sees when it validates your HTTPS — useful for catching expiry risks, chain misconfigurations, or TLS version problems.

Is the SSL checker free?

Yes, completely free with no signup. Check as many domains as you want — production sites, staging, internal subdomains accessible from the internet — no rate limits beyond abuse protection. All PingThat tools are in one open tier, which is why devs and sysadmins keep it in their bookmarks for quick cert sanity checks.

Does the SSL checker connect to external servers?

Yes, inherently. Checking an SSL certificate means actually opening a TLS handshake to the host and pulling its cert. The tool performs that handshake from the server side, then relays the result to your browser — your IP is not what connects to the target host. The hostname you check IS sent to the checker backend and to Certificate Transparency log APIs, since looking up CT entries requires it.

What does 'chain of trust' failure mean?

Every certificate is signed by an intermediate CA, which is signed by a root CA that browsers trust natively. If your server only sends the leaf cert and not the intermediate, modern browsers may fail to validate even though the cert itself is fine. The checker flags this explicitly: 'incomplete chain, intermediate missing'. Fix by including the intermediate cert in your server's cert bundle — your CA provides it.

Why does the checker say my cert expires soon even though I renewed?

The tool reports what the server is currently serving. If you renewed with your CA but haven't deployed the new cert to the server (or to your load balancer, CDN, or reverse proxy), the old one is still live. Also check you deployed to all hosts in a fleet — it's common to update one and forget the backup. Rerun the check after deployment to confirm the new validity dates are visible.

SSL Certificate Checker Online Free

SSL/TLS Test — Certificate Checker & HTTPS Validation

Enter a domain to check its SSL/TLS certificate status. See HTTPS connectivity, HSTS configuration, server info, and certificate transparency logs.

How to check an SSL certificate

Enter the hostname or full URL of the site you want to inspect.
The tool fetches the TLS certificate chain and parses issuer, subject, validity dates and SAN entries.
Review the expiration date and certificate chain for trust issues.
Use the cipher and protocol summary to confirm the server supports current TLS versions.

Common use cases

Verifying an SSL certificate is valid and trusted before a domain launch.
Catching certificates that expire in under 30 days before they break production.
Confirming that a renewal actually deployed to the load balancer serving a domain.
Auditing a vendor's TLS configuration during a security review.

Frequently asked questions

Why does the tool sometimes say 'chain incomplete'?

A missing intermediate certificate means some clients (especially older mobile) cannot verify the chain. Reinstall the cert with the full intermediate bundle from your CA.

What does SAN mean?

Subject Alternative Names — the list of hostnames the cert covers. Modern TLS does not rely on the Common Name, so the hostname you use must appear in the SAN list.

Can it check TLS versions?

Yes. The tool reports the negotiated protocol (TLS 1.2 vs 1.3) and the cipher suite, so you can spot servers still accepting deprecated versions.

Is my query logged?

No. The lookup runs through the browser and no query history is stored server-side.

Why check SSL certificates?

SSL/TLS certificates encrypt traffic between browsers and servers. An expired or misconfigured certificate can cause security warnings and lost trust.

HTTPS connectivity check
HSTS header detection
Certificate transparency logs
Response time measurement
Server identification

Free. No signup. Browser tools (subnet, JWT, password strength) run locally; lookup tools query public APIs (Cloudflare DoH, RDAP, certificate logs). Full per-tool breakdown at /methodology/.

Sources (3)

Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., & Polk, W. (2008). Internet X.509 Public Key Infrastructure Certificate and CRL Profile. RFC 5280, IETF.
Rescorla, E. (2018). The Transport Layer Security (TLS) Protocol Version 1.3. RFC 8446, IETF.
Hodges, J., Jackson, C., & Barth, A. (2012). HTTP Strict Transport Security (HSTS). RFC 6797, IETF.

These are the IETF RFCs, NIST publications, and W3C standards the tool implements or queries. Locate them on the IETF Datatracker (datatracker.ietf.org) or the official standards body.

Related guides

SSL Certificate Monitoring — What to Watch and When to AlertPractical guide to monitoring TLS certificates — expiry thresholds, CAA records, OCSP stapling, and what actually breaks in production.

By Marco B. · Last verified June 2026 — runs in your browser