Verify SSL/TLS certificate validity, expiry dates, issuer details, and security grade for any domain
Check any website's SSL/TLS certificate instantly with our free SSL certificate checker tool. Verify certificate validity, expiration dates, issuer details, Subject Alternative Names (SANs), signature algorithm, key size, and security grade in seconds. Essential for webmasters, developers, security professionals, and anyone who needs to monitor SSL certificates and prevent website outages caused by expired certificates.
An SSL certificate (Secure Sockets Layer certificate, now technically called a TLS certificate — Transport Layer Security) is a digital certificate that authenticates a website's identity and enables an encrypted, secure connection between a web server and a visitor's browser. The padlock icon you see in the address bar of every secure website is proof that an SSL certificate is installed and functioning correctly.
SSL certificates work through public key cryptography: the certificate contains a public key used to encrypt data sent from the browser to the server, while the server holds a matching private key used to decrypt it. This ensures that sensitive data — login credentials, credit card numbers, personal information — cannot be intercepted and read by third parties, even on compromised networks.
Beyond security, SSL certificates are now a foundational requirement for the modern web. Google has used HTTPS as a ranking signal since 2014, and browsers display alarming "Not Secure" warnings on HTTP sites, causing users to immediately leave. An expired or misconfigured SSL certificate is one of the most common causes of sudden drops in web traffic, e-commerce sales, and user trust.
The most basic type of SSL certificate. The Certificate Authority (CA) only verifies that the applicant controls the domain — typically through a DNS TXT record or a file placed on the web server. Issued within minutes.
Issuer examples: Let's Encrypt (free), ZeroSSL (free), Comodo, DigiCert.
Best for: Blogs, personal websites, development environments, small business sites that don't handle sensitive transactions.
The CA verifies both domain control and the existence and legitimacy of the organization requesting the certificate. Typically takes 1–3 business days. The certificate includes the organization's verified name.
Issuer examples: DigiCert, Sectigo, GlobalSign, Entrust.
Best for: Business websites, SaaS applications, customer portals, and any site where users need assurance they're dealing with a real company.
The highest level of certificate validation. The CA conducts thorough vetting of the organization's legal existence, physical location, and operational status. Historically showed a green address bar in browsers (now less visible in modern browsers).
Issuer examples: DigiCert, Entrust, GlobalSign (premium pricing).
Best for: Banks, financial institutions, e-commerce platforms, healthcare providers, and any site handling highly sensitive transactions.
A single wildcard certificate secures a domain and all of its first-level subdomains (e.g., *.example.com covers www.example.com, mail.example.com, api.example.com, etc.). Extremely cost-effective for organizations with many subdomains.
Limitation: Wildcard certificates don't cover second-level subdomains (e.g., app.api.example.com) and can be revoked if the wildcard private key is compromised, affecting all subdomains.
Also called UC (Unified Communications) certificates, SAN (Subject Alternative Name) certificates secure multiple different domain names within a single certificate. For example, one certificate can cover example.com, example.net, example.org, and example.co.uk.
Our SSL checker shows all Subject Alternative Names in the certificate, which tells you every domain and subdomain the certificate is valid for — important for verifying multi-domain deployments.
Created and signed by the server owner rather than a trusted Certificate Authority. Free to create but not trusted by browsers — users see a "Your connection is not private" warning. Used legitimately in internal development environments and testing but should never be used on public-facing production websites.
Our tool identifies self-signed certificates and shows them as not trusted, helping you quickly identify misconfigured production servers.
Shows exactly when the SSL certificate expires and how many days remain. Certificates typically have a maximum validity of 398 days (Apple's limit). Our tool color-codes warnings: green for valid, yellow when fewer than 30 days remain, red for expired.
Confirms whether the certificate is currently valid for the entered domain. A certificate might exist but be invalid for the domain queried (common hostname mismatch error), be expired, or be revoked.
Shows who issued the certificate — Let's Encrypt, DigiCert, Comodo, GlobalSign, etc. — along with the issuer's organization name and country. Helps verify you're using a trusted, recognized CA.
Lists every domain name the certificate is valid for. A certificate issued for example.com might also cover www.example.com, api.example.com, and other subdomains. This verifies whether all your subdomains are covered.
Shows the cryptographic key size (2048-bit RSA or 256-bit ECDSA are current standards) and signature algorithm (SHA-256 is current best practice; SHA-1 is deprecated and insecure). Helps identify weak or outdated cryptographic configurations.
An overall security grade (A+ to F) based on certificate configuration quality — similar to SSL Labs grading methodology. Takes into account key size, signature algorithm, certificate type, validity period, and other security factors.
Cryptographic hashes of the full certificate. Can be used to verify certificate identity, detect certificate substitution attacks, and confirm you're seeing the exact same certificate across different network paths.
The certificate version (should be v3 for modern certificates) and unique serial number assigned by the CA. The serial number is important for certificate revocation — CAs publish Certificate Revocation Lists (CRLs) identified by serial number.
Following SSL certificate best practices is essential for maintaining website security, SEO rankings, and user trust. Here are the most important guidelines:
Set up automatic certificate renewal and monitor expiry dates. Let's Encrypt certificates expire after 90 days but auto-renew at 60 days. For paid certificates, set renewal reminders 60+ days before expiry to allow time for validation.
Never use SHA-1 certificates (deprecated since 2017 and rejected by modern browsers). SHA-256 is the current standard. ECDSA (Elliptic Curve) certificates offer equivalent security with smaller key sizes and better performance.
2048-bit RSA keys are the minimum acceptable size. 4096-bit offers more security but slower handshakes. For new deployments, consider ECDSA P-256 which offers better performance and equivalent security to 3072-bit RSA.
Use wildcard certificates or SAN certificates to ensure every subdomain used in production is covered. A missing subdomain in the certificate causes browser errors and erodes user trust. Use our SSL checker to verify SAN coverage.
HTTP Strict Transport Security (HSTS) tells browsers to always connect via HTTPS, preventing protocol downgrade attacks. Implement HSTS with a long max-age (1 year minimum) after confirming your HTTPS setup is stable and permanent.
Certificate Transparency (CT) logs are public records of every certificate issued. Monitor CT logs for your domain to detect unauthorized certificates issued by rogue CAs — a key indicator of potential phishing attacks against your domain.
The relationship between SSL certificates and SEO is significant and multifaceted. Google officially confirmed HTTPS as a ranking signal in 2014, and the weight of this signal has grown steadily since. Here's how your SSL certificate directly impacts your search engine rankings and organic traffic:
Check your SSL certificate at least once a month, and set up automated monitoring to alert you when fewer than 30 days remain before expiry. For critical business websites, check weekly. Many SSL monitoring services (including paid uptime monitoring tools) can automatically alert you before certificates expire, preventing website outages.
When an SSL certificate expires, browsers immediately display a full-page security warning ('Your connection is not private' in Chrome, 'Warning: Potential Security Risk Ahead' in Firefox). Most users will immediately leave without proceeding. Search engine crawlers may also be blocked. This effectively takes your website offline for most visitors and causes rapid ranking drops.
From a cryptographic security standpoint, yes — Let's Encrypt certificates use the same encryption standards (RSA 2048-bit or ECDSA) as paid certificates from DigiCert or Comodo. The difference is in validation level (Let's Encrypt only offers Domain Validated certificates) and warranty (Let's Encrypt has no warranty). For most websites, Let's Encrypt is perfectly adequate. Banks and financial institutions typically require OV or EV certificates for regulatory and trust reasons.
A Subject Alternative Name (SAN) is an extension to the X.509 certificate standard that allows a single certificate to be valid for multiple domain names. Modern certificates require at least one SAN entry. If your www.example.com subdomain is not listed as a SAN in your example.com certificate, visitors to www.example.com will see a certificate hostname mismatch error. Our SSL checker displays all SANs to help you verify complete coverage.
SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are both cryptographic protocols for securing internet communications. TLS is the modern, secure successor to SSL. All versions of SSL (SSL 2.0, SSL 3.0) are now deprecated and insecure. Modern 'SSL certificates' actually use TLS 1.2 or TLS 1.3 for the actual connection — the term 'SSL certificate' persists as industry convention despite referring to what is technically a TLS certificate.
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