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To verify an SSL/TLS installation, check three things separately: the certificate covers the exact hostname, it is within its validity dates and the server sends the required intermediate certificates. Then use a deeper public-server assessment to inspect enabled TLS protocols, cipher suites and revocation information. A green HTTPS padlock alone does not prove that every hostname, client or protocol is configured correctly.
What a TLS checker can tell you
A TLS checker connects to a hostname and reports what that endpoint presents during a TLS handshake. The result depends on the hostname, port, network vantage point and the tool’s scope. A basic certificate checker generally answers:
- Is a certificate installed on the endpoint?
- Does the certificate’s subject or Subject Alternative Name cover the exact hostname?
- Has the certificate expired, or is it not yet valid?
- Are the required intermediate certificates being sent?
- Are there obvious certificate problems, such as an outdated hash algorithm?
A detailed TLS assessment goes further by examining protocol versions, cipher configuration and revocation-related information. It still assesses the server’s effective TLS configuration; it is not a general application penetration test. Qualys describes SSL Labs’ boundary plainly: “We never test for exploits.”
Choose the right test depth
Basic certificate installation check
Use a basic checker when a browser shows a certificate warning, a renewal has just been deployed, or you need to confirm that a web server sends the complete chain. Enter the public hostname exactly as visitors use it, including a subdomain such as www, api or mail. A certificate for example.com does not automatically cover every other name unless those names appear in the certificate’s Subject Alternative Name list.
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Check the reported identity, expiration date and chain findings. If your service is available through more than one hostname, CDN, load balancer or regional front end, test each applicable endpoint: a certificate can be correct on one TLS termination point and wrong on another.
Detailed public-server assessment
Use a deeper assessment when you need to know which TLS protocol versions and ciphers are accepted, or when you need revocation and configuration detail. SSL Shopper directs readers to SSL Labs for this level of analysis. TLS 1.3 behavior is defined by RFC 8446: the server’s end-entity certificate key and restrictions must be compatible with the authentication algorithm selected during the handshake, and the certificate is normally X.509v3. Thus, a certificate can exist and still fail with a particular client if the key type or negotiated parameters are incompatible.
Local testing for private endpoints
Public scanners cannot reach an internal hostname, VPN-only service or firewall-protected staging system. SSL Shopper recommends testing such an installation with OpenSSL from a machine that can reach it:
openssl s_client -connect hostname.example:443This command attempts a TLS connection and prints handshake and certificate information. It does not, by itself, enumerate every hostname, protocol, cipher, revocation method or browser trust decision. For SNI-sensitive virtual hosting, include the server name explicitly:
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openssl s_client -connect 203.0.113.10:443 -servername hostname.exampleUse an address only when it is the endpoint you intend to test; otherwise connect to the DNS name directly.
Step-by-step: verify a public SSL certificate
- Identify the endpoint. Record the exact hostname and port users reach, such as
shop.example.com:443. Note whether a CDN, reverse proxy or load balancer terminates TLS. - Run a certificate check. Submit the hostname to a basic SSL checker. Do not submit a private key or any secret credential.
- Read the hostname result. Confirm that the requested name appears in the certificate’s Subject Alternative Name entries. A certificate for the apex domain may not cover a separate subdomain.
- Read the dates. Record the “not before” and expiration dates. An expired certificate, or a server clock that makes a current certificate appear not yet valid, will trigger trust errors.
- Inspect the chain. Confirm that the server sends the leaf certificate plus the required intermediate certificates. Browsers may cache intermediates, masking an incomplete server configuration that breaks other clients.
- Review warnings. Treat obsolete hash algorithms, an unknown issuer, a hostname mismatch or an incomplete chain as configuration defects rather than cosmetic notices.
- Re-test the actual deployment point. If TLS is terminated at a proxy or CDN, fix the certificate there, not only on the origin server. Repeat the check from the same hostname after the change.
SSL Shopper says repeated SSL Checker results may be cached for up to one day. An immediate repeat can therefore show the previous certificate even after a successful deployment. Record the check time and hostname when communicating an incident.
How to read common findings
| Finding | What it means | Typical correction |
|---|---|---|
| Hostname mismatch | The requested DNS name is not covered by the certificate. | Install a certificate containing the exact name, including the required Subject Alternative Name entry, or correct DNS routing. |
| Expired or not-yet-valid | The certificate validity window does not include the current time. | Renew or replace the certificate and verify the server clock and the TLS termination point. |
| Missing intermediate | The server sends the leaf certificate but not the chain a client needs to build trust. | Configure the server or proxy with the certificate bundle that includes the required intermediate certificates. |
| Unknown issuer | The client cannot build a trusted path to a locally trusted root. | Use the correct publicly trusted chain for public services, or install the organization’s private root on managed clients for an internal service. |
| Old hash function | The certificate uses a legacy signature algorithm or other obsolete property. | Reissue with a currently accepted algorithm and confirm requirements with your certificate authority and platform documentation. |
| Protocol or cipher warning | The endpoint permits a protocol or cipher that the detailed assessment considers weak, obsolete or incompatible. | Change settings at the TLS termination point, then test client compatibility before disabling older options. |
Do not equate a valid certificate with a secure application. Certificate validation authenticates a name and establishes an encrypted channel; it does not find SQL injection, vulnerable dependencies, authorization errors or other application exploits.
Checking TLS protocols and ciphers
A basic certificate page is not the right instrument for protocol negotiation. Run a detailed public-server test when you need a supported-protocol matrix, cipher information or revocation details. Treat the report as a snapshot of the public endpoint seen by that service. SSL Labs’ API documentation notes that assessments run on Qualys servers and target SSL servers available on the public Internet.
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Protocol compatibility
Clients and servers must agree on a protocol and compatible authentication parameters. TLS 1.3, specified in RFC 8446, still requires a compatible X.509 certificate and key for the selected authentication algorithm. A failure limited to one client can therefore reflect protocol or key compatibility rather than certificate absence.
Do not copy stale cipher recipes
Protocol and cipher recommendations change as browsers, operating systems and standards evolve. The CA/Browser Forum maintains versioned Baseline Requirements for publicly trusted TLS server certificates. Verify any compliance or issuance claim against the current requirements and your web server’s current documentation instead of copying an old configuration snippet. Test changes on every supported client class before removing a protocol.
Public versus private testing
| Situation | Best first test | Why |
|---|---|---|
| Public website with a browser warning | Basic certificate checker, followed by a detailed public assessment if needed | Confirms identity, dates and chain before investigating protocols. |
| Public API behind a CDN or load balancer | Test the public API hostname; test each distinct front end if traffic can land elsewhere | The externally visible TLS terminator is what clients validate. |
| Internal or VPN-only hostname | OpenSSL from a host on the reachable network | Public services cannot connect to private names. |
| Staging server not exposed to the Internet | Local client testing and controlled internal scans | Keeps the endpoint private while allowing handshake inspection. |
Troubleshooting a failed check
“The certificate is valid, but browsers still warn”
- Check the exact hostname, including whether users are redirected between apex and
www. - Inspect the complete chain; an omitted intermediate is a frequent cause of client-specific failures.
- Verify the client and server clocks.
- Check whether a CDN, WAF or load balancer presents a different certificate from the origin.
“The checker cannot find my server”
Confirm public DNS, port 443 reachability and firewall rules. A private hostname is outside the scope of public checkers; run OpenSSL from an internal machine instead.
“The result did not change after renewal”
Allow for SSL Shopper’s stated cache period of up to one day on repeated checks. Also verify that the renewed certificate was installed on every TLS termination point and that DNS is reaching the intended endpoint.
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“Only one client fails the handshake”
Compare the client’s supported protocols, cipher suites and certificate-key requirements with the server’s detailed report. TLS 1.3 authentication still requires a compatible certificate key and restrictions; a successful connection from another client does not prove universal compatibility.
“The report is clean; are we secure?”
No. A clean TLS configuration report says what the tested public endpoint presents. SSL Labs explicitly does not test for exploits, so pair TLS verification with application security testing, patch management and access-control review.
Operational checklist
- Test the exact public hostname and port users use.
- Confirm Subject Alternative Name coverage.
- Check “not before” and expiration dates.
- Verify the server sends the complete intermediate chain.
- Use a detailed assessment for protocols, ciphers and revocation information.
- Use OpenSSL for internal or private endpoints.
- Record hostname, test location and timestamp with every result.
- Re-test after changing the certificate, proxy, CDN or load balancer.
- Check current CA/Browser Forum requirements and current software guidance before applying cipher changes.
- Never upload a private key to a checker.
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Python:
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Sources and scope
For protocol behavior, use RFC 8446. For publicly trusted certificate issuance and management, use the current, versioned CA/Browser Forum Baseline Requirements. SSL Shopper’s checker documentation defines its certificate, chain, hostname and expiration checks and notes its cache behavior; its guidance points to SSL Labs for deeper protocol, cipher and revocation analysis. Those tools answer TLS-configuration questions, not whether an application is free of exploitable defects.
Frequently Asked Questions
Can I use a public TLS checker for an internal hostname?
No. Public checkers require a reachable public endpoint. Run OpenSSL from a machine that can reach the internal service instead.
Why does a certificate checker show a chain error when my browser works?
Your browser may have cached or previously downloaded the missing intermediate certificate. Configure the server to send the complete chain so clients without that cache also build trust.
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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteDoes TLS 1.3 require a special certificate?
It requires a certificate type and key compatible with the authentication algorithm selected during the handshake, as specified by RFC 8446. It does not mean that every existing certificate will work with every client and configuration.
Is a detailed SSL Labs result a penetration test?
No. It evaluates effective public-server TLS configuration. Qualys states that SSL Labs does not test for exploits.
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