That little padlock in the address bar is doing more than you might think. It's the visible sign of an SSL certificate — the thing that encrypts everything between a visitor and a website, and quietly underpins trust on the entire web.
Here's what an SSL certificate actually is, why it matters, what goes wrong when one expires, and how to check any site's certificate for free.
What an SSL certificate does
An SSL certificate (technically TLS now) does two jobs. First, it encrypts the connection so that passwords, card numbers and everything else travel scrambled — no one in between can read them. Second, it verifies identity, confirming the site is really who it claims to be, so you're not handing data to an impostor.
When a site has a valid certificate, it's served over HTTPS and the browser shows the padlock. Without one, browsers now warn visitors that the site is 'Not secure.'
Why it matters — beyond security
- Trust — visitors (rightly) hesitate to enter anything on a 'Not secure' site.
- SEO — HTTPS is a Google ranking signal; secure sites have an edge.
- Functionality — modern browser features and many payment systems simply refuse to work without HTTPS.
- Data protection — without it, anything submitted can be intercepted on the network.
The thing that catches people out: expiry
Certificates don't last forever — they expire, often every 90 days for free ones. When a certificate lapses, every visitor hits a full-page security warning, forms stop being safe, and trust evaporates instantly. It's one of the most common and most avoidable site outages.
Automate renewal (free certificates from Let's Encrypt renew automatically) and keep a reminder well before the expiry date. A lapsed certificate is an emergency that's entirely preventable.
How to check a certificate
Check any site's certificate with the free SSL Certificate Checker. It shows whether the certificate is valid and trusted, when it expires (and days remaining), which hostnames it covers, the issuer, and the TLS version — all from a live connection.
SSL Certificate CheckerCheck a site's SSL certificate and expiry.For the fuller security picture, review your response headers with the HTTP Header Checker — HTTPS is the foundation, but headers like HSTS build on top of it.