What is an SSL certificate?
An SSL certificate (technically a TLS certificate) lets a website use HTTPS. It encrypts the connection between the visitor and your server, so passwords, card numbers and contact form messages cannot be read on the way. It also proves the site really belongs to the domain in the address bar. Browsers show a padlock for valid certificates and a full-page warning when something is wrong, which scares away almost every visitor.
Google has used HTTPS as a ranking signal since 2014, as announced on the Google Search Central blog. Today an expired certificate is one of the fastest ways to lose traffic and trust.
What this SSL checker tests
- Trust: is the certificate chain trusted by browsers?
- Hostname match: does the certificate cover the exact domain you entered?
- Expiry: how many days are left before it expires?
- Issuer, validity dates and the Subject Alternative Names (all domains covered)
- TLS protocol version and cipher in use
- The full certificate chain
How to check an SSL certificate
- Type your domain, for example
example.comorwww.example.com. - Click Check SSL.
- Look at the verdict at the top: green means all good, orange means it expires within 30 days, red means visitors will see a warning.
Check both the www and non-www versions of your domain. A common mistake is a certificate that covers only one of them.
Common SSL problems and fixes
- Expired certificate: renew it with your host. Free certificates from Let's Encrypt last 90 days and should renew automatically, so an expiry usually means the auto-renewal broke.
- Name mismatch: the certificate was issued for a different domain. Reissue it to include every domain and subdomain you use.
- Not trusted: often caused by a missing intermediate certificate. Install the full chain your provider gives you.
- Old TLS version: TLS 1.0 and 1.1 are outdated. Enable TLS 1.2 and 1.3 on your server.
After installing a certificate, make sure HTTP redirects to HTTPS using the Redirect Checker, and add the HSTS header, which you can verify with the HTTP Header Checker.
More security checks
A valid certificate is the foundation, but it is not the whole picture. Check your site's security headers with the HTTP Header Checker, and run a Website SEO Audit to confirm HTTPS works across the page. Use the Broken Link Checker to find old http:// links that should be updated to https://.
Types of SSL certificates
All certificates encrypt traffic in the same way. The difference is how much the certificate authority checks before issuing it:
| Type | What is verified | Typical use |
|---|---|---|
| Domain Validated (DV) | Control of the domain only | Blogs, business sites, most websites |
| Organization Validated (OV) | Domain plus the company's identity | Company and corporate sites |
| Extended Validation (EV) | Strict company checks | Banks and large brands |
| Wildcard | Covers all first-level subdomains (*.example.com) | Sites with many subdomains |
| Multi-domain (SAN) | Several different domains in one certificate | Agencies and groups of sites |
For most small business websites, a free DV certificate from Let's Encrypt is perfectly fine. Modern browsers no longer show the company name in the address bar for EV certificates, so the visual difference is gone.
Why certificates expire
Certificates have a maximum lifetime. Let's Encrypt certificates are valid for 90 days. For all public certificates, browser and certificate industry rules have been cutting the maximum lifetime step by step: since March 2026 it is 200 days, and it is scheduled to fall further to 47 days by 2029. Short lifetimes limit the damage if a key is ever stolen, but they mean renewal must be automatic. If your hosting or server does not renew automatically, set a calendar reminder at least two weeks before the expiry date shown by this checker.
How to renew or install a certificate
- cPanel hosting: most hosts include AutoSSL. Open "SSL/TLS Status" and click "Run AutoSSL".
- Ubuntu VPS with Nginx or Apache: install Certbot and run
sudo certbot --nginxorsudo certbot --apache. Certbot sets up automatic renewal; test it withsudo certbot renew --dry-run. - Cloudflare: set SSL mode to "Full (strict)" and install an origin certificate on the server.
After installing, check the domain here again to confirm the new expiry date and that the hostname matches.
Mixed content: the hidden HTTPS problem
A page can have a valid certificate and still show a warning if it loads images, scripts or styles over plain http://. This is called mixed content. Browsers block insecure scripts completely, which can break menus, forms or sliders. Search your theme and content for http:// links and change them to https://. The Website SEO Audit checks HTTPS and the HTTP to HTTPS redirect, and the HTTP Header Checker shows whether HSTS is enabled.
Why HTTPS matters for SEO and trust
Google has used HTTPS as a ranking signal since 2014, and Chrome labels HTTP pages as "Not secure". Visitors are far less likely to fill in a contact form or pay on a page with that warning. The article Why HTTPS matters on web.dev explains the benefits in more detail.
Frequently Asked Questions
How often should I check my SSL certificate?
Monthly is plenty, or set a reminder 30 days before the expiry date shown here.
Is a free SSL certificate as good as a paid one?
For encryption, yes. Paid certificates may add warranties or organization validation, but browsers show the same padlock.
Can I check a custom port?
Standard HTTPS ports 443 and 8443 are supported. Add the port after the domain, like example.com:8443.
Is this tool free?
Yes, completely free.
What does "certificate not trusted" mean?
The browser cannot link the certificate to a trusted authority. Usually the intermediate certificate is missing from the server, or the certificate is self-signed.
What is a hostname mismatch?
The certificate was issued for a different name. For example, it covers example.com but not www.example.com. Add both names when you request the certificate.
Does SSL slow down my website?
Modern TLS is very fast, and HTTPS enables HTTP/2, which often makes sites faster overall.
Last updated: October 25, 2026