How do I check if a TCP port is open online?

Enter your server's IP address or domain followed by a colon and the port number (e.g. 1.1.1.1:80 or example.com:443) and run a TCP check. The tool attempts a TCP handshake from 50+ global nodes and reports whether each connection succeeded, was refused, or timed out.

What is the difference between a port being refused versus timing out?

A refused connection (TCP RST) means the port is actively closed — the server replied to reject the connection. A timeout means no reply was received at all, which typically indicates a firewall is silently dropping packets before they reach the server or application.

Which TCP ports can I test?

Any valid TCP port from 1 to 65535. Common examples include port 80 (HTTP), 443 (HTTPS), 22 (SSH), 25 (SMTP), 3306 (MySQL), 5432 (PostgreSQL), and 3389 (RDP). No login or special permissions required — the check only verifies whether the TCP handshake completes.

My port is open locally but fails from external nodes — why?

If a port works locally but fails from external nodes, something between the internet and your server is blocking it — commonly a cloud security group, iptables rule, upstream ISP filter, or geoblocking policy. Running the check from multiple regions helps identify whether the block is global or specific to certain countries or ASNs.

Report for check-host.cc:80

Name: Check-Host check-host.cc:80 TCP 連接埠連通性測試
Author: Check-Host

Info Ping HTTP TCP UDP MTR DNS

Check TCP check-host.cc:80

Checked Apr 20, 2026 18:43:40 UTC |

| Check again |

Location	Result	Time	IP Address
Albania, Tirana	Connected	58.0 ms	34.36.183.77
Australia, Sydney	Connected	1.0 ms	34.36.183.77
Bosnia and Herzegovina, Novi Travnik	Connected	45.0 ms	34.36.183.77
Bulgaria, Sofia	Connected	26.0 ms	34.36.183.77
Canada, Montreal	Connected	1.0 ms	34.36.183.77
Switzerland, Bern	Connected	2.0 ms	34.36.183.77
Chile, Santiago	Connected	1.0 ms	34.36.183.77
China, Hohhot	Connected	260.0 ms	34.36.183.77
Germany, Nuernberg	Connected	4.0 ms	34.36.183.77
Germany, Frankfurt am Main	Connected	0.0 ms	34.36.183.77
Germany, Frankfurt am Main	Connected	0.0 ms	34.36.183.77
Germany, Limburg	Connected	2.0 ms	34.36.183.77
Germany, Frankfurt am Main	Connected	0.0 ms	34.36.183.77
Germany, Duesseldorf	Connected	5.0 ms	34.36.183.77
Denmark, Glostrup Municipality	Connected	12.0 ms	34.36.183.77
Spain, Bilbao	Connected	36.0 ms	34.36.183.77
Finland, Helsinki	Connected	18.0 ms	34.36.183.77
Finland, Helsinki	Connected	12.0 ms	34.36.183.77
France, Gravelines	Connected	5.0 ms	34.36.183.77
France, Paris	Connected	9.0 ms	34.36.183.77
United Kingdom, London	Connected	7.0 ms	34.36.183.77
Georgia, Tbilisi	ERROR	-	check-host.cc
Greece, Athens	ERROR	-	check-host.cc
Hong Kong, Hong Kong	Connected	5.0 ms	34.36.183.77
Croatia, Zagreb	Connected	176.0 ms	34.36.183.77
Hungary, Budapest	Connected	15.0 ms	34.36.183.77
Indonesia, Jakarta	Connected	17.0 ms	34.36.183.77
Israel, Petach Tikwa	Connected	2.0 ms	34.36.183.77
Israel, Netanja	Connected	3.0 ms	34.36.183.77
India, New Delhi	Connected	1.0 ms	34.36.183.77
Iceland, Reykjavik (Miðborg)	Connected	25.0 ms	34.36.183.77
Kuwait, Kuwait City	ERROR	-	check-host.cc
Lithuania, Pilaite	Connected	40.0 ms	34.36.183.77
Latvia, Riga	Connected	31.0 ms	34.36.183.77
Moldova, Chisinau	Connected	35.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	2.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	4.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	3.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	2.0 ms	34.36.183.77
Norway, Oslo	Connected	43.0 ms	34.36.183.77
Poland, Warsaw	Connected	18.0 ms	34.36.183.77
Romania, Bacău	Connected	34.0 ms	34.36.183.77
Romania, Bucharest	Connected	42.0 ms	34.36.183.77
Serbia, Belgrade	Connected	154.0 ms	34.36.183.77
Russia, St Petersburg	Connected	9.0 ms	34.36.183.77
Singapore, Singapore	Connected	1.0 ms	34.36.183.77
Turkey, Istanbul	Connected	31.0 ms	34.36.183.77
Taiwan, Taipei	Connected	4.0 ms	34.36.183.77
United States, Miami	ERROR	-	34.36.183.77
United States, Dallas	Connected	18.0 ms	34.36.183.77
United States, Kansas City	Connected	16.0 ms	34.36.183.77
United States, Dallas	Connected	5.0 ms	34.36.183.77
South Africa, Johannesburg	Connected	1.0 ms	34.36.183.77