About the Port Checker
The open port checker attempts a TCP connection from buffer.lol's server to a public host and port. It can confirm whether a service is reachable from an external network at the moment of the test.
How to use this tool
Enter a public hostname or IP address followed by a port, such as example.com:443. Confirm that the service is listening locally and that host, cloud, and perimeter firewalls allow the connection before testing. A successful result means the TCP handshake completed from the checker's network. For troubleshooting, compare the public hostname with its resolved address and verify any NAT or load-balancer forwarding rules.
How to read the result
An open result means a TCP connection was established; it does not verify that the application protocol returned correct data. A refused result usually means the destination actively rejected the connection or nothing is listening. A timeout can indicate filtering, routing trouble, silent firewall policy, or an unreachable host. Because these outcomes can vary by source network, compare the result with tests from an authorized machine in another location when needed.
Limits and privacy
The checker supports TCP reachability, not UDP scanning, service fingerprinting, or broad port ranges. Private, loopback, link-local, multicast, and other reserved targets are rejected, and only a single user-supplied port is tested. Firewalls may allow buffer.lol while blocking other sources, or do the reverse. Only test systems you own or are authorized to assess; the target is sent to the server to make the connection.
Common questions
- Does an open port prove the service is working?
- No. It proves only that a TCP handshake completed. The application behind the port can still be unhealthy or misconfigured.
- Why does a port time out instead of showing closed?
- Many firewalls silently drop connection attempts. That behavior produces a timeout rather than an immediate refusal.