Certline

Help Centre

Getting started

Certline tells you what TLS certificate a server actually presents right now. Paste a hostname into the box on the home page and press Check. Certline opens a real TLS connection to that server, reads the certificate it sends, and reports the expiry date, days remaining, the issuer, every hostname the certificate covers (the SANs), and whether the server sent its intermediate certificate.

Enter a hostname only — no https://, no path, no port. For example: example.com. The check runs on port 443 (standard HTTPS) and returns within seconds.

Common questions

Why does the page say "Hostname not found"?

The DNS lookup for the hostname you typed failed. Check the spelling, and confirm the host has a DNS record. If the hostname is correct and public, the lookup may be failing on the network the backend runs from — retry shortly.

Why does the check fail with "Connection refused" or "Connection reset"?

The server was reachable but did not complete a TLS handshake on port 443. "Connection refused" usually means nothing is listening on that port; "Connection reset" means the server closed the connection before the handshake finished. Both are about the server, not your certificate — check what is listening on :443 and that the service is actually serving HTTPS.

What does "incomplete chain" mean?

The server presented the leaf certificate but did not send the intermediate certificate that links it to a trusted root. Desktop browsers often paper over this from their own cache, so the site loads fine for you — but mobile clients and fresh browsers will reject it. This is the failure people lose a weekend to. Fix it by configuring the server to send the full chain (leaf + intermediate).

What does "server may be missing intermediate" mean?

The server sent only the leaf certificate and it is not self-signed, so its intermediate was not provided. Certline cannot always tell whether the backend completed the chain from its own store, so this is a warning rather than a definite diagnosis — check the TLS configuration on the server to confirm it is sending the full chain.

Why can't I check a hostname that's behind Cloudflare?

Certline's backend opens a direct TCP connection to the hostname you enter. Hosts that are fronted by Cloudflare (or similar CDN/proxy layers) may refuse or block that direct connection, so the check can fail even though the site loads fine in a browser. This is a known limitation of the current backend, not a problem with your certificate.

Is my data stored anywhere?

No. Certline does not store, log, or transmit any data you enter. Each check is ephemeral — the hostname goes to the backend, which reads the certificate, returns the result, and discards it. There are no accounts, no cookies, no analytics, and no tracking.

How much does Certline cost?

It is free. There are no accounts, no paid plans, and no billing. Nothing is charged and nothing is collected.

Known limitations

Certline is honest about what it does and does not do. It currently:

• Checks only the hostname you type — it never scans ranges, enumerates subdomains, or probes your neighbours. It is a single-point diagnostic, not an audit tool.
• Connects only on port 443 (standard HTTPS). It cannot check alternate ports or non-HTTPS services.
• Cannot reach Cloudflare-fronted origins reliably, as noted above.
• Does not send alerts, reminders, digests, or scheduled re-checks. There is no email sender in this fleet. Certline answers when you ask it; it will not notify you later, and the page will not pretend otherwise.
• Has no dashboard, accounts, or API key. You cannot save, watch, or compare results over time.
• Times out after 10 seconds on a slow connection. If a host is slow to answer, the check may report a timeout rather than a result.
• Reports what the server actually presented. If a field is absent, it is reported as absent — never inferred or filled with a typical value.

Contact us

Certline does not yet have a working support mailbox, so we cannot accept questions by email at this time. If you hit a problem the help above does not cover, please record it with the project owner — a verifiable contact route will be published here as soon as one exists.

For anything about these terms or privacy, see the Terms of Service and Privacy Policy.

Last updated: August 2026.