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.

Port Checker (Single Port) is designed to be straightforward: pick your input, choose the output settings, and generate a result you can copy or download. We focus on predictable defaults so you can get a usable output quickly, then fine-tune only when you need to.

If you’re using this tool for work, treat the result like any other export: verify a small sample first, then run the full job. Small checks (file size, encoding, preview, or a spot-check of values) prevent surprises later when you publish, upload, or share the output.

Quality and compatibility often pull in different directions. When you want maximum compatibility, choose widely supported options. When you want smaller size or faster delivery, pick modern formats and compression settings—but keep an original copy so you can re-export without compounding losses.

Privacy matters. Some tools run fully in your browser, while others may need server-side processing (for heavy conversions or specialized libraries). Where uploads are required, keep files non-sensitive and avoid including secrets in inputs. Always review the final output before sharing publicly.

Troubleshooting tips: if the output looks wrong, try changing one setting at a time, and confirm your input is what you think it is (color profile, transparency, encoding, delimiters, or line endings). Many issues come from an unexpected input variant rather than a broken converter.