Open Port Checker
Test whether TCP ports accept connections. Free, and checked from our server, so you see what the public internet sees — no sign-up or install.
About Port Checker
Each port is probed with a real TCP connection from outside your network, with a four-second timeout, and reported as open, closed or timed out. Up to twenty ports per run, and well-known ports are labelled with the service normally found there.
The three outcomes mean different things. A refused connection means something answered and said no — the host is reachable, nothing is listening. A timeout usually means a firewall dropped the packet silently, which is what a well-configured firewall does.
Where it helps
- Tests from the public internet, which is the view that matters for an exposed service.
- Twenty ports at once, so a firewall change can be verified in one go.
- Distinguishes refused from timed out, and those point at different causes.
- Well-known ports are annotated with their usual service.
- A table per run — port, service, status, response time and what actually happened — so a scan reads down one column.
Limits
- TCP only: UDP services such as DNS, DHCP and QUIC cannot be probed this way.
- Open means the handshake completed, not that the expected service is behind it.
- Private, loopback and link-local hosts are rejected, so internal networks cannot be scanned.
- Probe only hosts you are responsible for — port scanning other people's infrastructure is unwelcome and often prohibited.
Frequently asked questions
What is the difference between closed and timed out?
Closed means the host actively refused the connection — it is reachable with nothing listening. Timed out means no reply at all, typically a firewall dropping packets.
Why is the port open locally but closed from here?
The service is probably bound to 127.0.0.1 rather than 0.0.0.0, or a security group or firewall rule is blocking inbound traffic.
Can I check a UDP port?
No. UDP has no handshake, so there is nothing reliable to observe. This probes TCP only.
Is it acceptable to scan any host?
Limit yourself to infrastructure you own or have written permission to test. Unsolicited scanning breaches most acceptable-use policies.
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