Port Checker — Test Open TCP Ports

Test whether a specific TCP port is open on any public host. Our free port checker is perfect for firewall debugging, verifying services like SSH, HTTPS, SMTP, and MySQL are reachable from the public internet, and diagnosing 'connection refused' errors.

What a port checker does

A port checker attempts a TCP connection to a specific port on a remote host. If the connection succeeds, the port is open and a service is listening. If it times out, the port is filtered or closed.

When to test a port

After installing a new service (verify it is reachable), after a firewall change (confirm rules apply correctly), when a client reports 'connection refused', or when verifying that your hosting provider has not blocked an outbound port.

Why a port might appear closed

Firewall rules (cloud security group, iptables, ufw), the service is not running, the service binds to localhost only (127.0.0.1 instead of 0.0.0.0), or your hosting provider blocks the port by default (port 25 is famously blocked on most networks).

Common ports and their services
PortServiceNotes
22SSHRemote shell
25 / 465 / 587SMTP / SMTPS / SubmissionEmail — 25 often blocked
80HTTPUnencrypted web
443HTTPSTLS web
3306MySQLShould not be public
5432PostgreSQLShould not be public
6379RedisShould not be public
27017MongoDBShould not be public
8080 / 8443Alt HTTP / HTTPSApp servers, admin UIs

Frequently Asked Questions

How do I check if a port is open?

Enter the host and port above, click check. If we connect successfully, the port is open.

Is the port checker free?

Yes — free, unlimited tests, no signup.

Why is port 25 always blocked?

Most hosting providers and home ISPs block outbound port 25 to prevent spam. Use 587 (submission) or 465 (SMTPS) for email.

Can I scan multiple ports at once?

Currently single-port for ethics — please do not use this tool for unauthorised port scanning, which is illegal in most jurisdictions.

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