SSL Checker
Check the SSL certificate of any domain.
Check the SSL certificate of any domain.
This free SSL Checker from KX Toolkit is part of our all-in-one online toolkit. It runs entirely in your browser, so your data never leaves your device for client-side operations. 100% free, forever - no paywall, no credit card, no trial.
How to use the SSL Checker
- Enter the URL or domain.
- Pick the depth or check options if the tool supports them.
- Run the audit - results stream in as each check completes.
- Export the report or fix the issues flagged.
What you can do with the SSL Checker
- Pre-flight a new website before going live.
- Quick monthly health check on client sites.
- Diagnose why a page is slow or returning errors.
- Verify redirects after a domain or URL migration.
Why use KX Toolkit's SSL Checker
- Browser-based: Works on Windows, macOS, Linux, iOS and Android - no install, no extension.
- Privacy-first: Client-side tools never upload your data; server-side tools delete files right after processing.
- Mobile-friendly: Full feature parity on phones and tablets - not a stripped-down view.
- Fast: Optimised for instant feedback. No artificial waiting screens, no email-gated downloads.
- One hub for everything: 300+ tools across SEO, text, image, PDF, code, color, calculators and more - skip switching between sites.
Tips for the best results
Always run an audit BEFORE you publish, not after - most issues are easier to fix while the page is still in staging.
Related Website Management Tools
If you find this tool useful, explore the full Website Management Tools collection or browse our complete tool directory. KX Toolkit is built for marketers, developers, designers, students and anyone who needs a quick utility without signing up for yet another SaaS.
What does an SSL checker actually verify?
It validates the certificate chain (root, intermediate, and leaf certs all present and trusted), the certificate covers the requested hostname, the cert is not expired or not yet valid, the issuer is a trusted Certificate Authority, and the negotiated TLS version and cipher are secure. Advanced checkers also test for vulnerabilities like Heartbleed, BEAST, and weak ciphers. A green check is necessary but not sufficient; manually verify the cert details to catch subtle issues like missing intermediates that some browsers tolerate while others fail.
My SSL works in Chrome but fails in Firefox, what is wrong?
Almost always a missing intermediate certificate. Chrome caches intermediates aggressively and may use a previously seen one, while Firefox and mobile browsers do not. Re-issue the cert and ensure the full chain (server cert plus intermediate) is bundled in the .crt or PEM file you serve. Test with the SSL checker, which validates strict chain compliance. About 30% of "works for me" SSL issues are missing intermediates, especially with Let's Encrypt setups that miss the chain file in nginx.
How long should my SSL certificate validity period be?
Browsers limit publicly trusted certs to a maximum of 397 days, with some CAs moving to 90 days (Let's Encrypt has been 90 days from the start). Shorter validity is more secure because compromised keys roll over quickly, but requires automation. Set up auto-renewal at 30 days before expiry to handle outages. Manual annual renewals are increasingly impractical: missed renewals are one of the most common causes of unexpected site outages, often during off-hours when nobody notices for hours.
What is the difference between DV, OV, and EV certificates?
Domain Validated (DV) only verifies you control the domain, issued in minutes, and used by 95%+ of sites. Organization Validated (OV) additionally verifies your business identity, takes days, and shows extended details in cert info. Extended Validation (EV) does deep business verification and used to show a green company name in the address bar (browsers removed this UI in 2019, eroding the EV value proposition). For most sites, DV from Let's Encrypt or another free provider is sufficient and equally secure.
Why do I see mixed-content warnings even though my SSL is valid?
Mixed content means the page is HTTPS but loads at least one resource (image, script, stylesheet) over HTTP. Browsers either block these resources or warn users. The SSL cert is fine; the issue is hardcoded http:// URLs in your HTML, CSS, or JavaScript. Audit with the browser console (errors clearly list the offending URLs), then update them to https:// or protocol-relative //. Also check Content Security Policy headers, which can both detect and enforce HTTPS-only resource loading.
How often should I check my SSL certificate?
Set up automated monitoring with alerts at 30, 14, and 7 days before expiry; do not rely on manual checks. Tools like UptimeRobot, Better Uptime, and SSL Labs offer this for free. Additionally, run a deep SSL audit (SSL Labs Server Test) quarterly to catch new vulnerabilities like weak ciphers or protocol deprecations as standards evolve. Monthly SSL checks are insufficient because TLS 1.0 and 1.1 deprecations have caught many sites unaware between checks.
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