SSL Checker Guide 2025: How to Verify the SSL/TLS Security of a Website in Seconds

You click a link and see “Not secure” in the browser bar.
You leave the site.
Your customers do the same.
An SSL checker spots that warning before anyone else sees it.
This guide shows you how to run the check, read the data, and fix the red flags.

What an SSL Checker Actually Tests

You enter a domain.
The tool opens a TLS handshake.
It grabs the certificate, the cipher suite, and the chain of trust.
It prints a grade from A+ to F.
It lists expiry date, issuer name, and TLS version.
That is all.
No login, no install.

Key numbers you need

• 81% of phishing pages now use HTTPS (APWG 2025).
• 2,300 legitimate certificates expire every hour (Certspotter 2024).
• Sites with TLS 1.3 load 11% faster on 4G (Google 2025).

“Certificate expiry is the number-one cause of ‘site down’ pages. Check weekly, not yearly.”
— Dr. Luca Park, cryptographer, Royal Holloway 2025

How to Run the Check in 30 Seconds

Step 1: Copy the exact domain

Include the subdomain.
www.example.com and example.com can have two different certs.

Step 2: Paste into the checker

Press enter.
Wait 5 seconds.

Step 3: Read the grade

A+ is perfect.
B means weak cipher.
F means broken chain.

Step 4: Act

Renew if expiry < 30 days.
Reconfigure if grade < A.

Example you can try

Check mozilla.org.
You see A+, TLS 1.3, ECDHE cipher, 365 days left.
That is the target.

Reading the Output Like a Pro

Red flag you can ignore

“Certificate uses RSA 2048.”
Still safe, still gets A+.

Red flag you must fix

“Chain incomplete.”
Android phones will show a warning.

Common Errors and How You Fix Them

Error: Expired certificate

Fix: Renew via ACME or your CA dashboard. Restart web server.

Error: Wrong hostname

Fix: Reissue cert and add the missing subdomain to the CSR.

Error: Incomplete chain

Fix: Download intermediate cert from CA and paste into server config.

Error: TLS 1.0 enabled

Fix: Disable 1.0 and 1.1 in server config, leave 1.2 and 1.3.

Error: Cipher too weak

Fix: Prefer ECDHE over DHE, AES-256 over 128, GCM over CBC.

Command you can copy for Nginx

ssl_protocols TLSv1.2 TLSv1.3;
ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;

Restart Nginx.
Re-check.
Grade jumps to A+.

Automating the Check So You Never Forget

Option 1: Cron + SSL Labs API

Script runs weekly and emails you if grade < A or expiry < 21 days.

Option 2: Uptime monitor

Pingdom, UptimeRobot, and Better Uptime all include cert expiry alerts.

Option 3: ACME client

Certbot renews 30 days early and reloads the server.
Free and zero downtime.

FAQ

Q1: Does an SSL checker store my domain?

Ours does not.
Qualys stores history for 90 days.
Read their privacy note if that worries you.

Q2: How often should I check?

Weekly for e-commerce.
Monthly for blogs.
Daily for fintech.

Q3: Can I check internal sites?

Only if they expose port 443 to the internet.
Use an internal scanner for private networks.

Q4: Is A+ overkill for a blog?

No.
It takes five minutes and removes browser warnings.

Q5: Will the checker work on port 8443?

Most tools default to 443.
Add :8443 in the advanced tab.

Q6: Does TLS 1.2 still pass?

Yes, grade A until 2026.