SSL Checker

Connect to a site over HTTPS and read the security credentials its server presents: who issued them, which hostnames they cover and when they expire.

How to use it

1. Enter a hostname such as example.com.
2. Run the check.
3. Review the issuer, covered names, validity dates and status.

What you will see

• Subject – the main hostname the server identifies as.
• Issuer – the authority that signed it, such as Let's Encrypt or Sectigo.
• Valid from / until – the dates it can be trusted.
• Alternative names – every extra hostname covered, like www or subdomains.

Why check regularly?

An expired or mismatched credential triggers a full-screen browser warning that drives visitors away. Checking ahead of the expiry date — and after any server change — avoids surprises, even when renewal is automatic.

Common problems

• The www version is not covered
• Automatic renewal failed silently
• A CDN or proxy is serving an outdated copy

SSL or TLS?

"SSL" is the familiar name, but modern servers use its successor, TLS. The checker reads whatever the server sends on port 443.

Limitations

A valid result confirms encrypted connections only; it does not scan for malware or other vulnerabilities. Different subdomains or servers may present different credentials.

A worked example

A developer adds a new subdomain, shop.example.com, and visitors see a warning. The check shows the credentials cover only example.com and www.example.com. Reissuing them with the new name added solves the problem.

Free vs paid

Free authorities such as Let's Encrypt provide the same encryption strength as paid ones and renew automatically. Paid options can include organisation validation, warranties and support, which some businesses prefer.

Wildcards and subdomains

• A wildcard such as *.example.com covers every first-level subdomain.
• It does not cover the root name unless that is listed too.
• Deeper levels such as a.b.example.com need their own entry.

Routine checks

1. After adding a subdomain or moving hosts.
2. After CDN or proxy changes.
3. Monthly for important sites, even with auto-renewal.

Related tools

• SSL Certificate Checker – a detailed second view
• HTTP Headers Checker – check HSTS and security headers
• WWW Redirect Checker – confirm a single address

Step by step: checking after a server move

1. Run the check on the bare name and on the www version.
2. Confirm the issuer and expiry date match what you installed.
3. Check every subdomain you use, such as shop or blog.
4. Open the site in a private browser window to confirm there is no warning.

HSTS in brief

HTTP Strict Transport Security tells browsers to always use HTTPS for your site. It protects visitors from downgrade attacks, but once enabled it is remembered for months, so make sure every subdomain works over HTTPS before turning it on.