Port Check
Check the state of ports on an IP address or host name
Features
Check multiple ports at once
Specify up to 20 ports together and check their states at once in a list
Major ports with one tap
Instantly add 18 representative ports such as HTTP and SSH by button selection
Judge the state in 3 types
Show open, closed, and filtered in color and confirm the response time in milliseconds
Automatically show service names
List the expected service name corresponding to the port number in the result table
How to Use
Enter the host
Enter the host name or IP address in the "Host name / IP address" field
Specify the ports
Enter them comma-separated in the port field, or select with the representative-port buttons
Run the check
Pressing the check button lists the state and response time of each port
Use Cases
Checking server publishing settings
Verify whether web or mail ports are reachable from outside
Inspecting the firewall
Check for unintentionally open ports to grasp the security state
Isolating communication issues
Quickly determine whether the cause of a failed connection is a blocked port
Connectivity check after a service migration
Check whether the necessary ports are correctly listening on the new server
Basic Knowledge
What is a Port?
A port is a number (0–65535) that divides communication endpoints within a single server. Different services use standard port numbers, such as 80 (HTTP) and 443 (HTTPS) for the web, and 25 for email transmission.
Open, Closed, and Filtered
"Open" means the service is accepting connections on that port number; "closed" means the connection is explicitly refused (nothing is listening). "Filtered" means there is no response at all, which suggests firewall blocking.
Safety and Privacy
Server-side processing
Input is processed on the server; only information necessary for the inquiry is sent.
Temporary processing only
For checking the port state, temporary processing occurs on the server, then data is discarded after results are returned.
Communications encrypted with HTTPS
All sent and received data is encrypted by TLS and cannot be read by third parties.
No transmission to third parties
Input content is not sent to external services such as ad networks or trackers.
Connecting only to the target host
Only makes a connectivity-check connection to the entered host and ports, with no transmission elsewhere
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Updates
- update #17
Tidied up the port checker result layout to make key points easier to read