Open Port Checker

Why check if a port is open

A closed or filtered port means your service is unreachable — whether that's a web server on port 443, an SSH daemon on port 22, or a database accepting connections on 3306. The cause could be a firewall rule change, a crashed process, or a misconfigured cloud security group. This open port checker sends a TCP connection attempt to the host and port you specify and reports exactly what happened: open, closed, connection refused, or timed out, along with the response time in milliseconds.

Common situations where a quick port check saves time:

• Verifying a new firewall rule actually allows traffic through
• Confirming a service is listening after a deploy or server restart
• Troubleshooting connectivity issues between your app and a third-party API or database
• Checking whether your mail server (port 25 or 587) is reachable from outside your network

One-time checks vs. continuous monitoring

This tool gives you an instant, on-demand answer. That's useful for debugging, but ports don't stay open forever. A process can crash at 3 AM, a cloud provider can restart your instance, or someone can push a security group change that blocks traffic without realizing it. If a port matters to your application, you need something watching it around the clock.

Our port monitoring runs TCP checks on a schedule and alerts you through Slack, email, Telegram, or other channels the moment a port stops responding. You set the host, port, and check interval — we handle the rest, including response time tracking so you can spot rising latency before it turns into an outage.

Beyond port checks

Port availability is one layer of the stack. A port can be open while the service behind it returns errors. For web-facing services, pair port checks with uptime monitoring that validates HTTP status codes, response content, and SSL certificates. You can also use our HTTP status checker for a quick one-off test of any URL.

Infrastructure that depends on non-HTTP services — databases, cache servers, mail relays, custom TCP daemons — is exactly where port monitoring covers ground that traditional uptime checks miss.

Common ports