That little padlock in your browser's address bar depends entirely on one thing: a valid SSL certificate. When it's healthy, your connection is encrypted and trusted. When it expires or is misconfigured, visitors get a scary "Not Secure" warning — and many leave immediately. Whether you're a site owner guarding against an expiry disaster or just want to verify a site is safe, checking an SSL certificate takes seconds. Here's how to check a website's SSL certificate online, and what the results actually mean.

What is an SSL certificate?

An SSL certificate (technically TLS today) is a small digital file installed on a website's server. It does two jobs: it encrypts the connection between your browser and the site so no one can snoop on the data, and it proves the site's identity by being issued by a trusted Certificate Authority (CA). The presence of a valid certificate is what turns http:// into the secure https:// and shows the padlock.

Why check a website's SSL certificate?

Checking a certificate answers several important questions:

  • Is the site actually secure? Confirm the connection is encrypted and the certificate is valid.
  • When does it expire? Certificates have expiry dates, and an expired one blocks visitors with a security warning. For site owners, this is the single most important thing to monitor.
  • Who issued it, and is it trusted? See the Certificate Authority behind it.
  • Does it cover the right domain? A certificate issued for the wrong name triggers browser warnings.
  • Why am I seeing a "Not Secure" error? A quick check often reveals the exact cause.

How to check an SSL certificate online

The fastest way needs no technical knowledge: use a free online SSL checker. Enter a domain into our free SSL Certificate Checker and it retrieves the site's certificate and shows you the key details at a glance — its validity dates, who issued it, and whether it's currently valid. It works from any device, no browser digging required.

What the results tell you

When you run a check, here's how to read what comes back:

  • Validity dates (issued / expires). Every certificate has a "valid from" and "valid until" date. The expiry date is the one to watch — once it passes, browsers reject the site. Most certificates last from a few months to a year.
  • Issuer (Certificate Authority). The organization that issued the certificate, such as Let's Encrypt, DigiCert, or Google Trust Services. A certificate from a recognized CA is trusted automatically; a self-signed one is not.
  • Common Name and SANs. The certificate lists the domain(s) it covers — the Common Name plus any Subject Alternative Names. If you're checking www.example.com but the certificate only covers example.com, that mismatch causes warnings.
  • The certificate chain. A valid certificate links back to a trusted root through intermediate certificates. A missing intermediate ("incomplete chain") makes some browsers and apps reject an otherwise-valid certificate.

How to check a certificate in your browser

You can also inspect a certificate directly:

  1. Click the padlock (or "Not Secure") icon in the address bar.
  2. Choose Connection is secure → Certificate is valid (wording varies by browser).
  3. View the details — issuer, validity dates, and the domains the certificate covers.

This is handy for a quick look, though an online checker is easier when you want to test a domain you're not currently visiting, or check one that's throwing errors.

Common SSL problems a check reveals

Running a check often pinpoints exactly what's wrong:

  • Expired certificate — the most common issue, and it blocks every visitor until renewed.
  • Name mismatch — the certificate doesn't cover the exact domain being visited.
  • Self-signed or untrusted — not issued by a recognized CA, so browsers warn.
  • Incomplete chain — a missing intermediate certificate that breaks trust for some clients.

Any of these produces the errors covered in our guide on fixing "Your connection is not private" and SSL errors, and an incomplete chain or protocol mismatch can also surface as ERRSSLPROTOCOL_ERROR. Checking the certificate first tells you which problem you're actually dealing with.

For site owners: don't let your certificate expire

An expired SSL certificate is one of the most common — and most avoidable — causes of a site suddenly showing as unsafe or unreachable. The moment it lapses, browsers throw a full-page security warning and your traffic drops off a cliff.

To avoid it: know your certificate's expiry date, enable auto-renewal if your provider offers it (many, like Let's Encrypt, renew automatically), and check periodically to confirm renewals are actually working. If your site does go down or start warning visitors, run it through our live website down checker to confirm whether it's reachable at all, then check the certificate to see if an expiry is the cause.

The bottom line

Checking a website's SSL certificate is quick and genuinely useful: enter the domain into a free SSL Certificate Checker to see its expiry date, issuer, and whether it covers the domain — or click the padlock in your browser for a fast look. Read the validity dates first, confirm the issuer is trusted and the domain matches, and watch for an incomplete chain. For site owners, a periodic check (and auto-renewal) is cheap insurance against the sudden, self-inflicted outage of an expired certificate.