Open Port Checker — Free Online Tool

The Open Port Checker tests whether a specific TCP port on a host you specify is accepting connections from the public internet. A port that responds means a service is listening and reachable; a port that times out means it is either closed or being dropped by a firewall in front of it.

The distinction between "closed" and "filtered" is the useful part. A closed port typically refuses the connection immediately, while a firewalled port silently swallows the packet, so the request hangs until it times out. That difference tells you whether nothing is listening or whether something is listening but blocked — which is exactly the question when a service works locally but not from outside, the usual symptom of a security group, NAT rule, or host firewall that was never opened.

The ports people check most are the ones tied to a specific symptom: 80 and 443 when a site is unreachable, 22 when SSH from a new network stops working, 3306 or 5432 when an application cannot reach its database, and 25 or 587 when outbound mail fails — many hosting providers block those two by default, which surprises people every time.

Please only check hosts you own or are authorised to test. Scanning infrastructure you have no relationship with is, depending on jurisdiction, a violation of the operator's terms and potentially of computer misuse law. This tool checks individual ports on a host you name — it is a connectivity diagnostic, not a reconnaissance tool.

Our Open Port Checker is completely free to use with no signup required. For this tool, processing runs in your browser — your files and data stay on your device and are not uploaded to our servers.

Whether you are a developer, designer, student, or business owner, this tool is designed to save you time and make your workflow more efficient. Bookmark this page to access it whenever you need it — it will always be free.