SSL Certificate Checker
Check SSL certificate details, expiration dates, and security status for any domain. Verify certificate chains, issuer information, and protocol support for comprehensive security analysis.
About SSL Certificate Checker
A comprehensive SSL certificate checker that analyzes website security certificates, validates expiration dates, and examines certificate chains. This tool provides detailed information about SSL/TLS certificates including issuer details, validity periods, signature algorithms, and supported protocols to help ensure secure connections.
Why use a SSL Certificate Checker?
SSL certificates are critical for website security and user trust. Expired or misconfigured certificates can cause browser warnings, lost visitors, and security vulnerabilities. This tool helps monitor certificate health, prevent expiration-related downtime, verify proper installation, and ensure compliance with security best practices.
Who is it for?
Essential for webmasters monitoring certificate expiration, security teams conducting audits, developers troubleshooting SSL issues, and IT administrators managing multiple domains. Perfect for anyone responsible for maintaining secure websites or APIs who needs to verify certificate validity and configuration.
How to use the tool
Enter the domain name you want to check (e.g., example.com)
Click 'Check Certificate' to retrieve SSL certificate information
Review certificate details including expiration date and issuer
Check the certificate chain for proper validation
Analyze security warnings or recommendations for improvements
Frequently Asked Questions
How do I check an SSL certificate?
Enter a hostname (e.g., example.com) or full HTTPS URL. The tool establishes a TLS connection, retrieves the certificate chain, and displays: subject (the domain the cert was issued for), issuer (the Certificate Authority — Let's Encrypt, DigiCert, Sectigo, etc.), validity period (issued and expires dates), Subject Alternative Names (SANs — other hostnames the cert is valid for), public-key algorithm and size (RSA 2048+, ECDSA P-256), signature algorithm (SHA-256 with RSA or ECDSA), serial number, and the full chain back to a trusted root. Critical fields to verify: expiration date, SAN coverage of your hostname, and that the issuer is a CA you trust.
When does my SSL certificate expire?
The 'Valid Until' (or 'Not After') field in the certificate shows the exact expiration timestamp in UTC. Most browsers warn users 30 days before expiry; auto-renewal systems (Let's Encrypt's certbot, ACME-based tooling) typically renew at 30-60 days before expiry. This tool flags certificates expiring within 30 days as a warning. For ongoing monitoring, set up automated checks: a cron job querying the cert daily, alerting via email/Slack/PagerDuty if expiry is < 14 days away. Modern CAs (Let's Encrypt) issue 90-day certs that must be renewed every 60-75 days — this short lifetime is intentional, forcing automation that catches problems early.
Is online SSL checking safe and accurate?
Yes. The tool only reads the certificate that the server presents publicly during the TLS handshake — same data your browser sees on every HTTPS connection. No credentials, cookies, or session data are involved. The accuracy is exactly what TLS clients see: certificates are public by design, intentionally distributed to anyone who connects to the server. The check works for any publicly-reachable HTTPS endpoint. For internal/private servers behind a firewall, this tool cannot reach them — use OpenSSL locally instead: `openssl s_client -connect host:443 -servername host`. For Certificate Transparency log inspection, use crt.sh — that's a different lens on the same certificate data.
Why is my browser warning about an SSL issue?
Common causes: (1) Expired certificate — Valid Until date is in the past. (2) Hostname mismatch — the certificate's Subject or SANs don't include the hostname being visited (e.g., a cert for example.com is served when the user visited www.example.com without www listed). (3) Untrusted issuer — the cert chain doesn't end at a CA in the browser's trust store (common for self-signed certs in development). (4) Weak signature — SHA-1 signed certs are rejected by modern browsers since 2017. (5) Revoked cert — listed in CRL or OCSP. This tool surfaces all five categories. Fix at the source: renew, update SAN list, rebuild the chain, regenerate with SHA-256, or contact the CA for re-issuance.
What is SSL/TLS Certificate Transparency?
Certificate Transparency (CT) is a public, append-only log of every TLS certificate issued by a participating CA. Major CAs (Let's Encrypt, DigiCert, Sectigo, Google Trust Services) submit every cert they issue to multiple CT logs. Browsers (Chrome since 2018, Safari since 2020) require certs to be in CT logs — otherwise they're rejected. Why it matters: CT lets domain owners detect unauthorized certs issued for their domain (someone tricked a CA into issuing a cert for your-bank.com without your authorization). Tools like crt.sh and Censys let you monitor CT logs for your domains. CT doesn't prevent mis-issuance, but makes it loud enough to catch.
What's the difference between RSA and ECDSA certificates?
Same security goal, different math. RSA-2048 (the older default) uses 2048-bit keys based on factoring; certs are larger (~1KB), TLS handshakes are slower. ECDSA P-256 (modern default) uses 256-bit elliptic-curve keys based on the discrete log problem; certs are smaller (~256 bytes), handshakes are faster, equivalent cryptographic strength to RSA-3072. In 2026, most new certs are issued as ECDSA P-256 for performance; many large sites serve both via dual-cert deployments for legacy-client compatibility. For generating your own key pair when requesting a cert, use the [Key Pair Generator](/tools/key-pair-generator/) and select ECDSA P-256 unless a specific compatibility requirement mandates RSA.
What does the certificate chain look like and why does it matter?
A TLS certificate doesn't stand alone — it's signed by an intermediate CA, which is signed by a root CA, which the browser/OS trusts directly. The 'chain' is the leaf cert + all intermediates back to (but not including) the root. If the server doesn't serve the intermediates, some clients (older Android, Java, curl without ca-certificates) fail to validate. Always configure your web server to serve the full chain (typically a fullchain.pem from Let's Encrypt). This tool displays the chain and flags missing intermediates. If your cert validates in Chrome but fails in a backend API call, missing intermediates is a common cause.
How does this relate to DNS CAA records?
CAA records (queried via the [DNS Lookup](/tools/dns-lookup/) tool) authorize specific CAs to issue certificates for your domain. The flow: you publish a CAA record listing allowed CAs (e.g., 'letsencrypt.org'); CAs check this before issuing certs; if the issued cert is from an unauthorized CA, that's a major incident requiring revocation. After issuing a cert, use this tool to verify the issuer matches your CAA policy. If they don't match (e.g., CAA allows only Let's Encrypt but the cert was issued by Sectigo), something went wrong — either CAA was added after the cert was issued, or the CA didn't enforce CAA properly. Both warrant immediate investigation.
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