Skip to content
Education Host

Tools

SSL Certificate Checker

Check the SSL certificate for a domain, including issuer, expiry date, subject, validity period and common HTTPS details.

Add a port with a colon if needed — for example example.com:8443. Default is 443.

This checker opens a TLS connection to the host and reports the certificate it presents — issuer, validity dates, days remaining and the names it covers. Certificates that are expired, self-signed or mismatched are still shown, with the verification problem stated clearly.

Education Host runs your check for this request only. It is not stored in a database by this tool, although normal server and security logs may record requests like any other website.

The basics

What is an SSL certificate?

An SSL/TLS certificate proves a website's identity and enables the encrypted HTTPS connection between a browser and the server. Browsers only trust certificates that were issued by a recognised certificate authority, cover the hostname being visited and are still within their validity period.

When any of those conditions fails — expiry being the most common — visitors see security warnings instead of the website.

What a certificate contains

  • Subject — the hostname the certificate was issued for
  • Subject alternative names — every hostname the certificate covers
  • Issuer — the certificate authority that signed it
  • Validity window — the from/until dates browsers enforce
Expiry

Why SSL expiry matters

Certificate expiry is one of the most common causes of a website suddenly showing security warnings. Modern certificates are short-lived by design, so renewal has to happen regularly — and automated renewals can fail quietly until the day the certificate lapses.

  • Browsers show full-page warnings for expired certificates, and most visitors turn back
  • APIs, integrations and payment flows that call the site start failing
  • Mail, portals and other services behind the same certificate break at the same time
  • Automated renewal can fail silently — a scheduled check catches it early
Issuers

What does the issuer mean?

The issuer is the certificate authority (CA) that signed the certificate — organisations such as Let's Encrypt, Sectigo, DigiCert or GlobalSign. Browsers trust a certificate because they trust the authority that issued it, through a chain of signatures back to a root the browser ships with.

The issuer says nothing about the quality of the website itself — a free Let's Encrypt certificate encrypts traffic just as well as a paid one. What matters is that the chain verifies and the certificate stays in date.

If it is expiring

What to do about an expired or expiring certificate

Renewal is usually straightforward — the important part is knowing where the certificate is managed and confirming the renewal actually deployed.

  1. 1Find where the certificate is issued and managed — hosting control panel, a certificate provider, or automated tooling such as Let's Encrypt
  2. 2Renew or reissue the certificate before the valid-until date
  3. 3Install the renewed certificate everywhere the old one was used — web server, load balancer, CDN or mail services
  4. 4Re-check with this tool to confirm the new dates and that the chain verifies
  5. 5If renewal was meant to be automatic, find out why it did not run before the same thing happens again
More tools

Related tools

Part of a growing set of free Education Host checks.

IP Address Checker

See the public IP address your browser is using to reach this website.

Check your IP address

DNS Checker

Check DNS records for a domain, from A and MX to TXT, CAA and PTR.

Check DNS records

Blacklist Checker

Check whether an IP address appears on common DNS-based email blacklists.

Check blacklist status

IP Lookup

Look up technical details for an IP address, including classification and reverse DNS.

Look up an IP address

DMARC Checker

Check whether a domain has a DMARC record and review the published policy.

Check a DMARC record

Whois Lookup

Look up public domain registration information where available.

Run a Whois lookup
Browse all tools

SSL certificate checker — frequently asked questions

Answers to common questions about SSL certificates, expiry and HTTPS.

What is an SSL certificate?
An SSL/TLS certificate proves a website's identity and enables the encrypted HTTPS connection between a browser and the server. Browsers only trust certificates issued by recognised certificate authorities and still within their validity period.
How do I check when an SSL certificate expires?
Enter the domain in the checker above — it connects to the host over TLS and shows the certificate's valid-from and valid-until dates, plus the number of days remaining.
What does SSL issuer mean?
The issuer is the certificate authority (CA) that signed the certificate — such as Let's Encrypt, Sectigo or DigiCert. Browsers trust a certificate because they trust its issuer.
What does "expired" mean?
The certificate's valid-until date has passed. Browsers show full-page security warnings for expired certificates, and most visitors will not proceed past them.
What does "expiring soon" mean?
The certificate is still valid but has 30 days or less remaining. Renewal is often automatic with modern hosting, but a certificate this close to expiry is worth confirming.
Why does a site need HTTPS?
HTTPS encrypts traffic between visitors and the site, protecting logins, forms and personal data. Browsers flag plain HTTP pages as not secure, and search engines expect HTTPS as standard.
Can Education Host help fix SSL certificate issues?
Yes. Education Host provides SSL certificates and managed hosting for education organisations, and can help diagnose expired, misconfigured or mismatched certificates.
Does Education Host store SSL checks?
This tool runs your check for the current request and does not store it in a database. Normal server and security logs may record requests like any other website.