SysAdmin Tools

An SSL checker lets you inspect the TLS certificate installed on any domain and verify that it is valid, trusted, and correctly configured. Whether you are a sysadmin monitoring production sites, a developer debugging HTTPS errors, or a business owner making sure your website is secure, an online SSL certificate checker gives you all the details you need in seconds.

SSL — more accurately called TLS (Transport Layer Security) today — encrypts the connection between a user's browser and your web server. But having a certificate installed is not enough. It must be issued by a trusted Certificate Authority (CA), the certificate chain must be complete with all intermediate CAs present, the domain name must match the certificate's Subject Alternative Names (SANs), and the certificate must not be expired. Our SSL checker validates every one of these conditions with a real TLS handshake to your server — not a cached database lookup.

The tool extracts the full certificate chain, the negotiated TLS version and cipher suite, SANs, fingerprints, serial number, and the days remaining until expiry. It also detects whether the certificate is self-signed, whether it was issued by Let's Encrypt or a commercial CA, and whether the server's hostname matches the certificate. All results are presented clearly so you can identify problems immediately and take action before your certificate expires and causes site outages.

How to Use the SSL Certificate Checker

  1. 1

    Enter the domain name

    Type the domain you want to check — for example, google.com or api.example.com. You can include https:// or www; they are stripped automatically. The check always targets port 443.

  2. 2

    Click Check SSL

    The tool establishes a live TLS connection to the server, performs a full handshake, and retrieves the peer certificate and its complete chain. This takes a few seconds.

  3. 3

    Review the security checklist

    Six checks are shown at a glance: Chain Trusted, Full Chain Present, Hostname Match, Not Expired, Expiry > 30 Days, and TLS Version. Green means pass, amber means warning, red means fail.

  4. 4

    Inspect certificate details

    Scroll down to see the full certificate breakdown: issuer, subject, validity dates, SANs, cipher suite, serial number, SHA-256 fingerprint, resolved IP addresses, and the complete certificate chain visualisation.

Understanding SSL Certificate Check Results

The SSL checker returns several categories of information about the certificate installed on your domain. The top status card shows the overall result — Valid, Expiring Soon, Self-Signed, or Invalid — alongside the number of days until expiry. A certificate that expires in fewer than 30 days should be renewed immediately to avoid browser warnings that drive users away. The security checklist flags the six most important conditions: whether the CA chain is trusted by standard root stores, whether the intermediate CA certificate is present in the chain (missing intermediates cause "untrusted" errors in some browsers), whether the domain name matches the certificate's Common Name or SANs, and whether the TLS version is current. TLS 1.3 is the gold standard; TLS 1.2 is still acceptable; older versions are deprecated and dangerous. The Technical Details card shows the negotiated cipher suite, which indicates the encryption strength of the connection.
FieldDescription
Chain TrustedWhether the certificate chain traces back to a root CA trusted by major operating systems and browsers.
Full Chain PresentWhether intermediate CA certificates are included in the server's TLS response. Missing intermediates cause trust errors on some clients.
Hostname MatchWhether the queried domain matches the certificate's Common Name (CN) or any Subject Alternative Name (SAN).
Days RemainingNumber of days until the certificate expires. Negative values mean the certificate has already expired.
TLS VersionThe TLS protocol version negotiated during the handshake — TLS 1.3 is preferred, TLS 1.2 is acceptable.
Cipher SuiteThe encryption algorithm negotiated between client and server during the TLS handshake.
Subject Alt NamesThe list of domain names and subdomains the certificate covers, as defined in the SAN extension.
SHA-256 FingerprintA unique hash of the certificate used to identify and verify it independently of the issuer.

Common SSL Certificate Check Use Cases

Monitor certificate expiry before renewal

Set a reminder to run an SSL check 60 days before your certificates are due. Certificates that expire cause immediate site outages and browser security warnings. Checking early gives you time to renew through your CA or Let's Encrypt without rush.

Debug HTTPS errors after deployment

After deploying a new server or updating a certificate, run the SSL checker to confirm the chain is trusted, the hostname matches, and the intermediate CA is present. Most "NET::ERR_CERT_AUTHORITY_INVALID" errors are caused by a missing intermediate certificate.

Audit wildcard and multi-domain certificates

For wildcard (*.example.com) or SAN certificates covering many subdomains, the SSL checker lists all covered names so you can confirm every required hostname is included before go-live.

Verify TLS version compliance

Security standards like PCI DSS and SOC 2 require TLS 1.2 or higher. Use the SSL checker to confirm that legacy TLS 1.0 or 1.1 is not being negotiated on any customer-facing endpoint.

SSL Certificate Checker — Frequently Asked Questions

What is an SSL certificate?
An SSL certificate (technically a TLS certificate) is a digital document that binds a domain name to a cryptographic public key. It is issued by a Certificate Authority (CA) and enables encrypted HTTPS connections. Browsers display a padlock icon when a valid certificate is detected. Without one, browsers show security warnings that deter visitors and harm SEO rankings.
How do I check if my SSL certificate is valid?
Enter your domain in the SSL checker above and click Check SSL. The tool makes a live connection to your server and evaluates the certificate against six criteria: chain trust, chain completeness, hostname match, expiry status, days remaining, and TLS version. A green checklist means your certificate is correctly configured. Any red or amber flags need immediate attention.
What does SSL certificate expiry mean?
Every SSL certificate has a validity period — typically 90 days for Let's Encrypt or up to one year for commercial CAs. After the expiry date, browsers refuse to connect and show a "Your connection is not private" error. The SSL checker shows exactly how many days remain and flags certificates expiring within 30 days as a warning, giving you time to renew before users are affected.
What is TLS 1.3 and why does it matter?
TLS 1.3 is the latest version of the Transport Layer Security protocol, standardised in 2018. It is faster (requires one fewer round-trip than TLS 1.2) and more secure (removes weak cipher suites and compression). TLS 1.0 and 1.1 are deprecated and insecure. Most compliance frameworks now require TLS 1.2 as the minimum, with TLS 1.3 strongly recommended for new deployments.
What are Subject Alternative Names (SANs)?
SANs are a certificate extension that lists every domain name and IP address the certificate is valid for. A certificate might cover example.com, www.example.com, api.example.com, and *.staging.example.com all in one. The Common Name (CN) field is deprecated for hostname validation — browsers rely entirely on SANs. The SSL checker displays all SANs so you can verify every required hostname is covered.
What is a certificate chain?
A certificate chain is the sequence of certificates from your domain's end-entity certificate up through one or more intermediate CA certificates to a root CA that browsers trust. Browsers do not trust end-entity certificates directly — they must verify the full chain. If an intermediate CA certificate is missing from your server's response, some clients will show trust errors even though the certificate itself is valid.
Why is my SSL certificate not trusted?
The most common causes are: (1) a missing intermediate CA certificate — your server is not sending the full chain; (2) a self-signed certificate — no trusted CA signed it; (3) the certificate has expired; (4) the domain does not match any SAN on the certificate. The SSL checker's security checklist identifies exactly which condition applies so you can fix the right thing.
What is the difference between SSL and TLS?
SSL (Secure Sockets Layer) is the predecessor to TLS (Transport Layer Security). SSL 2.0 and 3.0 are long deprecated due to critical vulnerabilities. Modern HTTPS uses TLS 1.2 or TLS 1.3. The term "SSL" persists in everyday language even though every current implementation actually uses TLS. When people say "SSL certificate," they mean a certificate used with TLS.
How early should I renew my SSL certificate?
Renew at least 30 days before expiry, ideally 60 days. This gives you time to handle unexpected issues with the CA validation process. Let's Encrypt certificates (90-day validity) should be auto-renewed by certbot at the 60-day mark. Commercial CA certificates often have a longer lead time for domain validation. The SSL checker flags any certificate with fewer than 30 days remaining as a warning.
What does "certificate issued by Let's Encrypt" mean?
Let's Encrypt is a free, automated, and open Certificate Authority operated by the Internet Security Research Group (ISRG). It issues domain-validated (DV) certificates that are fully trusted by all major browsers. Let's Encrypt certificates are valid for 90 days and are designed to be renewed automatically using tools like certbot. They are indistinguishable from paid certificates in terms of encryption strength — the only difference is they lack Extended Validation (EV) status.

Related Tools

DNS Lookup

Verify the A record and CAA records for the domain alongside its certificate.

Security Headers

Check HSTS, CSP and other HTTP security headers that work alongside your SSL certificate.

WHOIS Lookup

Check domain expiry and registrar details while you review the SSL certificate.