Port Checker (Single Port)

This port checker tests a single TCP port on a public host and reports whether it’s open, closed or filtered, along with connect time and the resolved IP. It’s built for quick diagnostics: verifying a new firewall rule, checking if a service is reachable from outside your network, or confirming that a port forward/DMZ rule is actually exposed. Port ranges are intentionally blocked and timeouts are short to keep probes safe.

Use it before asking someone to allowlist you: enter the host and port, copy the result as JSON, and share the connect timing plus any error notes. If the status is filtered, a middlebox or firewall likely dropped the SYN/ACK; if closed, the host actively refused the connection or nothing is listening. Open indicates a completed TCP handshake, not full application health—pair this with HTTP ping or a service-specific check when needed.

Because SSRF protections reject private/reserved addresses, you can’t accidentally scan internal networks. Tests are single-target, single-port to reduce noise on the destination and to respect rate limits. Timeouts default to ~1.5s (configurable up to 3s), giving fast feedback without hanging your tab.

Common scenarios: confirming 443/8443 reachability to a reverse proxy, testing 22/2222 before enabling SSH from the internet, checking whether CGNAT blocks inbound connections, or verifying that a port forward on home broadband really exposes the intended device. Results are formatted for quick copy/paste into tickets and runbooks.

If you see inconsistent results, repeat the check from multiple networks—some ISPs filter uncommon ports or apply intrusion prevention that can rate-limit successive connects. Combine with traceroute or ping to see where filtering may start if the TCP handshake never completes.