FTP connection tester with FTPS certificate check

Yes. The tester never logs in and never asks for or sends credentials. It reads what the server sends before authentication (the SSH banner and algorithm list, or the FTP banner, FEAT and TLS handshake) and then disconnects. Results aren't stored.

Explicit FTPS connects in plain text on port 21 and upgrades with the AUTH TLS command before login. Implicit FTPS starts TLS immediately, usually on port 990. Explicit is the modern default. Implicit is older but still used by some devices and clients.

No. FTP sends the username, password and files unencrypted, so anyone on the network path can read them. Use FTPS or SFTP. If the tester shows AUTH TLS in the feature list, the server already supports explicit FTPS.

Usually because it's self-signed, has expired, or the server doesn't send the intermediate certificates. Clients then show a warning or refuse to connect. A certificate from a public CA such as Let's Encrypt, with the full chain configured, fixes it.

The test runs from our servers on the public internet, so it can only reach public addresses. Host names that resolve to private, loopback, link-local or reserved addresses are refused, and only ports 21, 22, 990 and 1024–65535 are allowed. Each visitor can run 10 tests per 10 minutes.

A passing test means the server is reachable and speaking the protocol. Login problems are usually the username, password or SSH key, or an IP allowlist on the server. For FTP and FTPS, also check the passive port range: the tester doesn't open data connections, and blocked passive ports are the most common cause of listings that hang.