Paste a domain and instantly verify certificate validity, expiry date, hostname/SAN match, intermediate chain, TLS versions, ciphers, OCSP stapling, HSTS, and more. Get clear fixes for common issues.

When a padlock looks “okay” but users still see warnings, you don’t have hours to spelunk server configs. You need a fast, trustworthy answer: Is the certificate valid? Does it match the hostname? Is the chain complete? Are we serving modern TLS without weak ciphers? That’s exactly what an SSL Checker delivers. Paste a domain (optionally with a port), and in a few seconds you’ll get a clean pass/fail summary plus detailed findings and practical next steps.

Everything below is written from scratch to be plagiarism-safe and SEO-friendly. It’s designed to help developers, admins, marketers, and support teams understand what the tool checks, why it matters, and how to fix problems without guesswork.

Quick refresher: “SSL” vs. “TLS” (and why the distinction matters)

We still say SSL out of habit, but modern encrypted web traffic uses TLS. Browsers have long disabled legacy SSL protocols. An SSL Checker is really a TLS health checker—it verifies that your site presents a valid certificate and negotiates secure, up-to-date protocols and ciphers.

Bottom line: don’t panic about the name; do make sure your site supports TLS 1.2 and TLS 1.3, and that older protocols are off.

What the SSL Checker actually tests

When you run a check on example.com (or example.com:8443 if you use a nonstandard port), the tool performs a handful of network-safe probes and reports results in plain language:

1) Certificate basics

• Validity window: Not Before / Not After dates (with a friendly days-to-expiry countdown).
• Issuer & trust: Whether the certificate chains to a trusted public CA.
• Key & signature: Public key type/size (e.g., RSA-2048, ECDSA P-256) and signature algorithm (e.g., SHA-256).
• Hostname match: Common Name and Subject Alternative Name (SAN) coverage—including wildcard behavior (*.example.com covers foo.example.com but not example.com).
• Revocation signals: OCSP stapling status and CRL availability (helpful for compliance).

2) Chain and intermediates

• Chain completeness: The server must present required intermediate certificates. Missing or out-of-order intermediates trigger “works in some browsers, fails in others” headaches; the checker flags this instantly.
• Cross-signed paths: Notes multiple valid paths and which one the server presents.

3) Protocols and ciphers

• TLS versions: Support for TLS 1.3 (preferred) and TLS 1.2; flags if TLS 1.0/1.1 remain enabled.
• Cipher suites: Highlights strong, forward-secure suites (ECDHE) and warns on weak/obsolete ones (e.g., RC4, 3DES, export-grade, static RSA key exchange).
• Forward secrecy: Verifies ephemeral key exchange (ECDHE/DHE) so past traffic can’t be decrypted if a key leaks.

4) Modern web signals

• HSTS: Presence of the Strict-Transport-Security header and its max-age, includeSubDomains, and preload directives.
• ALPN & HTTP versions: Whether the server advertises HTTP/2 and/or HTTP/3 (QUIC) via ALPN.
• SNI behavior: Notes if the certificate varies correctly by Server Name Indication for multi-tenant hosts.
• Certificate Transparency (CT): Presence of embedded SCTs (increasingly expected by browsers).

5) Helpful extras (optional)

• Redirects to HTTPS: A quick check that http:// cleanly upgrades to https://.
• Mixed content hints: A lightweight fetch to spot obvious insecure asset links on the landing page (useful post-migration).
• CAA records (informational): DNS CAA entries that restrict which CAs may issue for your domain.

Why these checks matter (in real life)

• Expiry causes outages. A certificate expiring on a weekend leads to panicked rollbacks and lost revenue. A countdown alert buys you time.
• Hostname mismatches break trust. If the SAN doesn’t include the exact host (or the wildcard isn’t appropriate), users see scary warnings.
• Intermediates are the silent culprit. Many “it works on my laptop” incidents trace to a missing intermediate on the server.
• Old protocols = audit failures. Keeping TLS 1.0/1.1 alive for “one legacy client” can fail compliance checks.
• Weak ciphers & no PFS increase risk. Even if the padlock shows, your traffic may be easier to attack.
• HSTS prevents mistakes. It turns accidental http:// requests into https:// automatically and helps with secure-by-default posture.
• ALPN clarifies performance. Knowing that HTTP/2 or HTTP/3 is active explains latency and multiplexing behavior.

How to use the SSL Checker (it’s genuinely simple)

1. Enter the host (and port if not 443). You can paste https:// or just the domain.
2. Run the scan. In a couple of seconds you’ll see a summary card (pass/warn/fail) plus details.
3. Review the certificate block. Check expiry, issuer, SAN coverage, key type, and signature at a glance.
4. Scan chain results. If you see “missing intermediate,” fix that first—it cures a surprising number of browser warnings.
5. Confirm protocols & ciphers. Look for TLS 1.3/1.2 and forward-secure ciphers; plan to disable legacy suites.
6. Note HSTS & ALPN. If absent, consider adding HSTS (with care) and enabling HTTP/2/3 if your stack supports it.
7. Save a report. For audits or tickets, export the findings and attach them to your change or incident record.

Interpreting common findings (and how to fix them)

“Certificate expires in 7 days”

• Why it happens: Manual renewals or automation hiccups.
• Fix: Renew now. If you use Let’s Encrypt or another ACME CA, confirm the ACME client runs and has permission to write challenges or update DNS. Add monitoring so you’re alerted at 30/14/7/3 days.

“Hostname mismatch”

• Why: The requested host isn’t in the SAN list, or you’re relying on a wildcard in the wrong place.
• Fix: Re-issue a certificate that includes every host users visit (www, apex/root, and any app subdomains). Remember that *.example.com does not cover example.com itself.

“Chain incomplete / missing intermediate”

• Why: The server is sending only the leaf certificate.
• Fix: Install the CA’s intermediate bundle and serve it with the leaf cert. Most platforms accept a “fullchain” file; use it.

“Old TLS versions enabled (1.0/1.1)”

• Risk: Fails many audits; some clients may negotiate weaker security.
• Fix: Disable TLS 1.0/1.1. Keep TLS 1.2 (with modern ciphers) and enable TLS 1.3 if available.

“Weak or non-PFS cipher suites”

• Why: Legacy compatibility settings.
• Fix: Prefer ECDHE+AES-GCM/ChaCha20-Poly1305, drop static RSA key exchange, remove RC4/3DES/export suites.

“OCSP stapling disabled”

• Impact: Revocation checks are slower and less reliable.
• Fix: Enable OCSP stapling on the server so clients can verify revocation status without contacting the CA directly.

“No HSTS header”

• Consider: HSTS protects against protocol downgrade and mixed-mode navigation.
• Fix: Start with a conservative max-age (e.g., a week), monitor, then extend (e.g., 6–12 months). Only consider preload after you’re confident all subdomains support HTTPS.

“HTTP/2 or HTTP/3 unavailable”

• Consider: Not a security bug, but enabling them can improve performance (multiplexing, lower latency).
• Fix: Update TLS stack/ALPN settings; ensure proxies and CDNs are configured to advertise the protocols you want.

Best-practice checklist (copy/paste into your runbook)

• TLS versions: Enable TLS 1.3 and 1.2; disable 1.0/1.1.
• Cipher suites: Use ECDHE key exchange; prefer AES-GCM or ChaCha20-Poly1305; remove weak/legacy suites.
• Certificates:
  • Key: RSA-2048+ or ECDSA P-256/P-384
  • Sig alg: SHA-256 or better
  • SAN: include all hostnames (apex + www + apps); use wildcards carefully
  • Chain: serve full chain (leaf + intermediates)
• Revocation: Enable OCSP stapling where supported.
• HSTS: Add Strict-Transport-Security after validating full HTTPS coverage; consider includeSubDomains later; preload only when ready.
• ALPN: Advertise h2 and h3 if your platform supports them.
• SNI: Ensure correct cert is returned for each SNI host behind load balancers/cert muxers.
• Automation: Use ACME for renewals; alert at 30/14/7/3 days pre-expiry; store contact emails with the CA.
• Documentation: Keep a certificate inventory (hosts, issuers, expiry dates, owners) and a one-page TLS policy shared across teams.

Who benefits from an SSL Checker

• Developers & SREs: Fast triage during incidents; confirm fixes after a deploy or cert renewal.
• SecOps & compliance: Evidence for audits—protocols, ciphers, HSTS, CT, revocation—captured in one report.
• Platform & IT teams: Validate load balancers, CDNs, and origin servers present the right cert per SNI.
• Marketing & product: Quick sanity check post-rebrand (new domains) or after turning on “force HTTPS.”
• Customer support: Translate browser errors into concrete steps (“Missing intermediate—install fullchain”).

Workflows that pay off immediately

1) Pre-launch cutover

Before pointing DNS to a new host, run the checker against the staging hostname. Fix mismatches and chain issues while traffic is low.

2) Post-renewal verification

After renewing (manual or ACME), scan the domain to confirm the new Not Before date is in effect on all edges (CDN + origin + failover).

3) CDN + origin alignment

If you terminate TLS at a CDN and re-encrypt to origin, run checks against both endpoints. Ensure modern TLS and correct certs on each leg.

4) Multi-domain/SAN housekeeping

Quarterly, export a list of SANs and compare to your active host inventory. Retire unused names; add new ones before they cause outages.

5) Incident retro

Attach the checker report to your post-mortem (e.g., “expired leaf cert on api.example.com, no alert fired”). Turn the fix list into backlog items.

Limitations (honest and useful)

• No private keys or server code: The checker only sees what any client can see during a TLS handshake.
• Client-side oddities: Some enterprise proxies or very old clients behave differently than a standard probe; test those separately if required.
• Content security isn’t audited: The tool focuses on transport encryption (TLS). App-layer issues (XSS, CSRF, CSP headers) are out of scope.

FAQs

Does “valid certificate” mean end-to-end security?
It means the connection is encrypted and the certificate is trusted for that host. App-layer security still matters.

Should I choose RSA or ECDSA?
Both are secure when configured well. ECDSA offers smaller certificates and faster handshakes; many sites deploy dual certs to support older clients.

Do wildcard certificates cover the apex domain?
No. *.example.com covers sub.example.com but not example.com. Include the apex explicitly.

What is OCSP stapling and do I need it?
It lets your server “staple” a fresh revocation proof from the CA to the TLS handshake. It improves privacy/performance and is recommended.

Is HSTS preload worth it?
Only after you’re 100% certain all subdomains are HTTPS-only. Preload is sticky and requires formal removal to undo.

Why does my site pass locally but fail for some users?
Usually a missing intermediate or SNI/cert muxing issue. The checker’s chain and SNI notes will point you toward the fix.

Suggested hero image & alt text

Concept: A minimalist dashboard titled “SSL Checker — Certificate & TLS Report” showing a green “Valid” badge with days to expiry, a card listing Issuer, SANs, Key (ECDSA P-256 / RSA-2048), Signature (SHA-256), and a second panel summarizing TLS 1.3 / TLS 1.2, Forward Secrecy: On, HSTS: Enabled, OCSP stapling: Active; a small side strip lists Findings with gentle green/amber/red indicators (e.g., “Chain complete,” “TLS 1.0 disabled”). Neutral UI, no real domains.

Alt text: “Certificate report showing validity, SANs, and issuer alongside TLS protocol and security features with simple pass/warn badges.”

Final takeaway

A padlock isn’t a diagnosis. An SSL Checker turns vague browser warnings into clear, actionable steps: confirm the certificate, fix the chain, modernize TLS & ciphers, and enable guardrails like HSTS and OCSP stapling. Make it part of your deployment checklist and renewal routine, and you’ll spend less time firefighting and more time shipping—securely.