SSL Checker

SSL Checker opens a real TLS handshake to any domain and turns the raw certificate into a plain-English bill of health: is it valid, how many days until it expires, does it cover the hostname you typed, is the certificate chain complete, and which TLS versions does the server actually speak. No X.509 dump to decode, just the answers a site owner needs, in about two seconds.

Certificates in one minute

An SSL/TLS certificate does two jobs. It encrypts the connection between a browser and your server, and it proves identity: that the server answering for yourdomain.com is really yours. That proof works through a chain of trust. A Certificate Authority (CA) your device already trusts signs an intermediate certificate, and that intermediate signs your certificate. A browser trusts your cert because it can follow that chain back to a root it was born knowing.

A few fields on the certificate matter in daily life:

• Common Name and SANs. The hostnames the certificate is valid for. Modern certs carry the real list in the Subject Alternative Name (SAN) field. If the host you typed isn’t in it, browsers reject the cert with a name-mismatch error, even though everything else is fine.
• Validity window. A not-before and a not-after date. Public certificates now max out at ~398 days of validity, so renewal is a recurring fact of life.
• Key and signature. The key type and size (RSA 2048, EC P-256) and the signature algorithm. A SHA-1 signature or a sub-2048-bit RSA key is a red flag on any modern certificate.

The chain is where it quietly breaks

The single most common “it works for me but not for them” bug is an incomplete chain. Your server is supposed to send your certificate and the intermediate certificate(s) above it. Desktop Chrome and Safari often paper over a missing intermediate by fetching it themselves, so it looks fine on your laptop. But many Android versions, older devices, curl, and the API clients and bots that talk to your site machine-to-machine can’t do that fetch, and they see an untrusted certificate. SSL Checker inspects the chain the server actually serves, not the idealised one, so a missing intermediate shows up before your integrations start failing.

Expiry is an outage waiting on a calendar

An expired certificate is one of the most damaging avoidable outages there is: every visitor hits a full-page browser warning, most leave instantly, and every API or webhook that calls you starts failing at the same moment. It’s entirely preventable. The expiry countdown is the first thing this tool shows, colour-coded: comfortable above 30 days, warning inside a month, alarm inside a week or already expired. If your issuer is an automated CA like Let’s Encrypt or ZeroSSL (certificates that renew every 90 days), the tool notes it, because a short validity window is a feature there, not a problem. The durable fix for everyone else is monitoring plus auto-renewal. Don’t rely on remembering.

TLS versions: which handshakes your server still speaks

TLS has four versions you’ll see in the wild, and the guidance is simple. TLS 1.2 and 1.3 are current and good. TLS 1.0 and 1.1 were deprecated in 2021, are refused by up-to-date clients, and fail PCI-DSS compliance; offering them is pure downside. SSL Checker probes each version and badges what the server offers. One honest caveat it surfaces: a modern server stack sometimes can’t even test an ancient protocol because its own libraries refuse to speak it, so the tool says “couldn’t test” rather than pretending a version is absent. For the deep cipher-suite audit a security team needs, SSL Labs remains the gold standard and takes a couple of minutes; this tool gives you the everyday 95% in seconds.

For AI agents

This tool exposes a plain-text endpoint designed for language models and agents:

GET https://nitrosites.com/tools/ssl-checker/scan.php?url=<target>&format=agent

It returns a token-cheap digest of the same analysis shown on this page. Soft rate limits apply; results are cached briefly. No key or login required.

Frequently asked questions

How do I know when my SSL certificate expires?

Run your domain through this checker. The expiry date and a day countdown are the first thing you'll see. Set a reminder at 30 days out, or use a certificate with auto-renewal like Let's Encrypt.

What happens when an SSL certificate expires?

Browsers show a full-page security warning and most visitors leave immediately. APIs and integrations that call your site start failing too. It's one of the most damaging avoidable outages a site can have.

What is an incomplete certificate chain?

Your server must send the intermediate certificate(s) alongside your own. Some browsers paper over a missing intermediate, but many devices, bots and API clients can't, so the site "works on my machine" while quietly failing for others. This tool checks the chain the server actually serves.

Should TLS 1.0 and 1.1 be disabled?

Yes, they've been deprecated since 2021 and fail PCI-DSS compliance. Your site should offer TLS 1.2 and 1.3 only; this checker shows exactly what's on offer.

Is this the same as an SSL Labs scan?

No, SSL Labs runs a deep multi-minute cipher audit and is excellent for security teams. This tool gives you the 95% you usually need (validity, expiry, chain, protocols) in about two seconds.