What is the SSL Checker?
The SSL Checker inspects a domain's live TLS certificate by opening a real TLS handshake with it on port 443 — not by asking a third-party certificate database. It reports whether the certificate is currently valid, when it expires, who issued it, which hostnames it covers, and the length of the trust chain back to a root certificate authority. Enter a domain and it returns the same information a browser checks silently before showing the padlock icon, made readable: expiry countdown, protocol version, cipher, subject alternative names and a plain-English explanation of any error found along the way.
Because the check performs an actual handshake rather than reading a report, it can detect and describe problems a browser would otherwise just silently block — expired certificates, self-signed certificates, and hostname mismatches are all handled and explained rather than causing the check itself to fail.
Why use a free ssl checker?
Live handshake, not a cached report
Connects directly to the domain on port 443 for every check, so the result reflects the certificate actually being served right now, not a snapshot from a scan run hours or days earlier.
Reports on broken certificates instead of just failing
Expired, self-signed and untrusted certificates still complete the handshake and get analysed, so you get a specific diagnosis instead of a generic connection error.
Full certificate chain length
Counts how many certificates link your site's certificate back to a trusted root — a broken or incomplete chain is a common cause of "not secure" warnings on some devices even when the certificate itself is fine.
Every subject alternative name listed
See every hostname the certificate actually covers, so you can confirm a subdomain wasn't missed before it starts throwing browser warnings.
Expiry countdown with urgency flags
Days remaining are shown directly, with the result flagged when a certificate is inside its final two weeks of validity.
How do you use the SSL Checker?
- 1
Enter the domain
Type the domain, without "https://" — e.g. example.com. The check always connects on port 443.
- 2
Read the status badge
Valid, Expired, Self-signed or Not trusted — the headline result tells you immediately whether visitors would see a warning.
- 3
Check days remaining and the chain
Days remaining shows your renewal runway. Chain length confirms the certificate links properly back to a trusted root.
- 4
Confirm every hostname you use is covered
Scan the subject alternative names list for every subdomain your site actually serves — a certificate covering example.com does not automatically cover shop.example.com.
How accurate is it?
The check opens a genuine TLS connection to the domain on port 443 and reads the certificate the server actually presents, the same one any visitor's browser would receive. It deliberately accepts invalid or expired certificates during the handshake, rather than rejecting the connection, specifically so it can report on exactly what is wrong instead of just failing.
- This tests port 443 (standard HTTPS) only. A server running TLS on a non-standard port will not be checked correctly by this tool.
- Trust is evaluated using Node.js's built-in certificate authority store, which closely mirrors what major browsers trust — but is not identical to any single browser's exact CA list, so a small number of edge cases can differ from what a specific browser shows.
- The chain length counts certificates by following the issuer link presented during the handshake. A server that fails to send its full intermediate chain will show a shorter chain here than it should — which is itself a real, fixable misconfiguration worth flagging.
- A hostname resolving to a load balancer or CDN edge node in front of multiple origin servers may show a different certificate on different checks if those origins are configured inconsistently.
What should you know before using it?
What common browser SSL/TLS errors actually mean:
| Browser error | What it means |
|---|---|
| NET::ERR_CERT_DATE_INVALID | The certificate has expired, or its "valid from" date is in the future. Check the expiry date and renew. |
| NET::ERR_CERT_COMMON_NAME_INVALID | The certificate doesn't cover the hostname being visited — the domain or subdomain is missing from the subject / subject alternative names. |
| NET::ERR_CERT_AUTHORITY_INVALID | The certificate was issued by an authority the browser doesn't trust — commonly a self-signed certificate or an incomplete chain missing an intermediate certificate. |
| Self-signed certificate warning | The certificate was signed by itself rather than a trusted CA. Fine for local development, a hard stop for a public production site. |
| NET::ERR_SSL_PROTOCOL_ERROR | Often a server-side misconfiguration — no valid certificate presented at all, or a fundamentally broken TLS setup on that port. |
| Certificate chain incomplete | The server sent its own certificate but not the intermediate certificate(s) linking it to a trusted root — some browsers still work via caching, others fail outright. |
Which tools relate to the ssl checker?
The ssl checker is one of 18 domain & ip tools on this site. These are the ones most often used alongside it — either because they handle the next step in the same job, or because they answer a question this tool raises.
HTTP Headers Checker
A valid certificate secures the connection; HSTS, set in the response headers, is what forces browsers to always use that secure connection going forward.
DNS Records Lookup
Before checking a certificate, confirm the domain's A or AAAA record actually points at the server you expect to be serving it.
WHOIS Lookup
Registration status and expiry are a separate concern from certificate expiry — check both independently, since a domain can be registered fine with an expired certificate or vice versa.
Meta Tag Analyzer
Once the site loads securely, check that its on-page meta tags are set up correctly for search results.
When should you use a ssl checker?
The ssl checker queries live public records, so it suits checks where a stale answer would be misleading — during a migration, after a DNS change, or before you commit to a domain. These are the situations people reach for it in most often.
Renewal monitoring
Check days remaining before a certificate expires, especially for certificates managed manually rather than through auto-renewal like Let's Encrypt.
Post-deploy verification
After a server or load balancer change, confirm the certificate being served is the right one, covers the right hostnames, and has a complete chain.
Diagnosing "not secure" reports from users
When a visitor reports a browser warning you can't reproduce, check whether their exact hostname is covered by the subject alternative names and whether the chain is complete.
Vendor and subdomain audits
Check the certificate on every subdomain in use — marketing pages, APIs, staging environments — since it is common for one to be missed during a certificate renewal.
Frequently asked questions
How do I check if a website's SSL certificate is valid?
What does "self-signed certificate" mean?
How many days before expiry should I renew a certificate?
What is a certificate chain, and why does its length matter?
What are subject alternative names (SANs)?
Does this tool check SSL on a custom port?
Is checking someone else's SSL certificate this way legal?
Is the ssl checker safe to use?
This tool sends the domain you enter to our server, which opens a direct TLS connection to that host on port 443 and reads the certificate it presents. This mirrors exactly what a browser does on every HTTPS page load — no private data is accessed — but avoid pointing this at internal-only hostnames or infrastructure not meant to be probed from outside your network.
Where do these figures come from?
Every method, threshold and standard this page relies on, with a link to the document that defines it. Check them — a tool that will not show its sources is asking you to take its word for it.
- 1The Transport Layer Security (TLS) Protocol Version 1.3
IETF, RFC 8446 · 2018
Supports: The description of the TLS handshake this tool performs to retrieve and validate the certificate a server presents.
- 2Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
IETF, RFC 5280 · 2008
Supports: The definitions of the certificate chain, issuer linkage and subject alternative names reported for each certificate.
- 3Baseline Requirements for the Issuance and Management of Publicly-Trusted Certificates
CA/Browser Forum
Supports: The requirement that a publicly trusted certificate chain back to a trusted root CA, referenced in the chain-length explanation.
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