SSL Certificate Checker

Inspect TLS certificates, issuer details, SAN entries, and expiration status
This free online ssl certificate checker runs in your browser and is part of our Developer Tools collection.

SSL Certificate Checker

Inspect a server certificate for issuer, validity dates, subject names, and chain basics.

What this helps with

  • Check certificate expiration timelines before outages
  • Verify SAN coverage for multi-domain deployments
  • Validate issuer and TLS handshake basics quickly
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Instant In-Browser Execution Runs locally in JavaScript without wait times or server delays.
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100% Privacy & Security Your inputs and files are never stored or logged on remote servers.
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Cross-Device Responsive Fully optimized for mobile smartphones, tablets, and desktop displays.
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100% Free Forever No subscription fees, no signups, and no software installations.

How to Use the Online SSL Certificate Checker

1 Enter Hostname & Port

Type the domain name (e.g. `github.com`) and port (default 443).

2 Initiate TLS Handshake

Click "Check SSL" to perform a TLS certificate inspection.

3 Review Validity & Expiration Days

Inspect Valid From, Valid Until, exact days remaining until expiration, and active renewal alert status.

4 Examine Issuer & SAN Domains

Review the Certificate Authority (e.g. Let's Encrypt, DigiCert, Cloudflare), key signature algorithm, and all Subject Alternative Name (SAN) domain aliases.

Frequently Asked Questions

Common questions about using this free online ssl certificate checker.

Why is monitoring SSL certificate expiration critical? ▾
When an SSL/TLS certificate expires, browsers immediately block access with severe security warnings ("Your connection is not private"), devastating site traffic, brand trust, and revenue.
What are Subject Alternative Names (SANs)? ▾
SAN extensions allow a single SSL certificate to secure multiple different domains and subdomains (e.g. `example.com`, `www.example.com`, and `api.example.com`).
What is the standard validity lifetime for modern SSL certificates? ▾
Industry standards (CA/Browser Forum) mandate a maximum validity of 398 days (approximately 13 months) for public TLS certificates, with automated Let's Encrypt certificates renewing every 90 days.
What TLS protocol versions are considered secure today? ▾
TLS 1.2 and TLS 1.3 are secure and recommended. Legacy SSL 2.0, SSL 3.0, TLS 1.0, and TLS 1.1 have critical vulnerabilities and are blocked by modern browsers.

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