Free SSL Certificate Checker — Verify Any Website’s TLS Certificate Instantly

Check the SSL/TLS certificate of any domain in real time. Enter a hostname above
and our tool connects directly to port 443, fetches the live X.509 certificate,
and displays every relevant detail in a single view — no account required.

What This SSL Checker Does

Our certificate inspection tool performs a full TLS handshake with the target
server and retrieves the presented certificate chain. It parses the DER-encoded
certificate on the backend and returns structured information you can act on.

You get immediate access to the Common Name, the issuing Certificate Authority, both valid-from and valid-until dates, the exact number
of days remaining before expiry, the certificate’s serial number, and
its SHA-256 fingerprint for verification against Certificate Transparency
logs. Subject Alternative Names (SANs) are listed in full — critical when
checking wildcard coverage or multi-domain configurations. You also see the
public key type and size (RSA bit-length or EC curve) and the
signature algorithm used to sign the certificate.

If the certificate has already expired, the tool highlights this clearly.
Certificates expiring within 30 days are flagged with a warning.

When to Use an SSL Certificate Checker

A TLS checker is useful for system administrators, DevOps engineers, and
security professionals who need to:

  • Verify a new deployment — after installing or renewing a certificate,
    confirm the correct chain is being served before notifying stakeholders.
  • Monitor third-party services — check that vendors and API partners have
    valid SSL certificates and haven’t let them lapse.
  • Debug browser warnings — when a visitor reports a “not secure” warning,
    pull up the live certificate to diagnose whether the issue is expiry,
    hostname mismatch, or a missing intermediate.
  • Audit internal infrastructure — scan internal hostnames to catch
    self-signed or soon-to-expire certificates before they break production.
  • Prepare for compliance audits — gather certificate details for PCI DSS,
    SOC 2, or ISO 27001 evidence collection without logging into every server.

How It Compares to openssl s_client

Many administrators reach for the command openssl s_client -connect crtmgr.com:443 -servername crtmgr.com to inspect a certificate. Our web-based
SSL checker gives you the same data through a browser, formatted for readability:

  • No need to install OpenSSL or navigate terminal output.
  • Expiry countdown calculated automatically instead of manual date math.
  • SANs parsed and listed line-by-line.
  • Fingerprint displayed in the standard colon-separated hex format recognized by
    Certificate Transparency monitors and CA/B Forum tools.

API Access for Automation

For scripted checks and CI/CD pipelines, the SSL checker is available as a REST
API that returns structured JSON. Always use HTTPS — Cloudflare enforces it:

Linux / macOS (curl):

curl -s "https://api.crtmgr.com/api/v1/ssl-checker?domain=crtmgr.com" | python3 -m json.tool

Windows (PowerShell):

Invoke-RestMethod -Uri "https://api.crtmgr.com/api/v1/ssl-checker?domain=crtmgr.com" | ConvertTo-Json -Depth 5

Windows (cmd):

curl -s "https://api.crtmgr.com/api/v1/ssl-checker?domain=crtmgr.com"

The API responds with a JSON object containing domain, cn, issuer,
not_before, not_after, days_left, expired, serial_hex,
fingerprint_sha256, sans (array), key_type, key_size, and
signature_algorithm. See the full API documentation for details.

Certificate Transparency and Fingerprint Verification

Every certificate returned includes the SHA-256 fingerprint. You can cross-check
this value against public Certificate Transparency logs (such as
crt.sh/?q=crtmgr.com) to confirm that the certificate you see is the same one
logged by the issuing CA. This is a recommended practice when investigating
potential man-in-the-middle scenarios or verifying that a newly issued
certificate has propagated through CT logs.

Supported Certificate Types

The tool works with any publicly reachable HTTPS server on port 443. It supports
RSA and ECDSA keys, certificates issued by Let’s Encrypt, DigiCert, Sectigo,
GlobalSign, Amazon Trust Services, Google Trust Services, and any other
CA trusted by the Mozilla root program. Wildcard certificates and multi-domain
(SAN) certificates are fully parsed.

Rate Limits

To keep the service fast for everyone, SSL certificate checks are limited to a
few requests per minute per visitor. Results are cached in your browser for five
minutes, so refreshing the same domain won’t consume additional quota.

If you need to check certificates in bulk, consider integrating with the
public API directly.

Related Tools

CSR Generator — if the certificate you just checked is
about to expire, create a new Certificate Signing Request with the correct SANs
and key type for your renewal.

Find Your Public IPv4 and IPv6 — detects your current public IPv4 and IPv6 addresses

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