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Global probes
Confirm connectivity from a neutral network to rule out local firewall rules or ISP filtering.
Free Online Tool
Port Checker
Port Checker is the dedicated port checker for SRE, DevOps, and security engineers to validate connectivity, share common port checker knowledge, and respond to outages faster. This port checker keeps your investigations focused on the exact services that matter.
Free online port checker
LiveEnter an IP address or hostname with a target port to verify connectivity from our cloud-based port checker probe.
Always confirm you have permission before scanning or testing endpoints you do not own.
Instant port testing
Engineered for the Port Checker workflow
Modern operators need fast answers. Port Checker combines live port checker testing, best practices, and documentation in one place so the port checker workflow stays consistent for every team member.
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Actionable guides
Each featured port includes setup checklists, troubleshooting flows, and security reminders.
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Operations ready
Crafted for on-call teams with responsive design, dark mode, and multilingual support.
How it works
How this open port checker tests your connection
The test runs from an external network, so it shows whether a service is reachable from the public internet rather than only from your local machine.
01
Enter a target
Provide a public IP address, IPv6 address, or hostname and the TCP port you want to check.
02
We connect from outside
Port Checker sends a TCP connection attempt from a cloud probe, similar to how a remote client would reach your service.
03
The response is measured
A successful handshake means the port is open. A rejection, timeout, or blocked packet points to a closed or filtered path.
04
You get a clear result
Use the result to verify port forwarding, firewall changes, cloud security groups, and service availability.
Result meanings
What open, closed, and filtered usually mean
A port check is a point-in-time connectivity test. Read the status with your firewall, router, ISP, and application configuration in mind.
The target accepted a TCP connection on that port.
Confirm the exposed service is expected, patched, authenticated, and monitored.
The host was reachable, but nothing accepted the connection on that port.
Check whether the service is running, listening on the right interface, and allowed through the firewall.
Packets were dropped or blocked, so the exact port state could not be confirmed.
Review router forwarding, security groups, ACLs, ISP filtering, CGNAT, and source-IP allowlists.
Instant port testing
Popular ports at a glance
Jump straight into the guides for the ports Port Checker users ask about most often, then run a port checker against each service to confirm availability.
Port
HTTPS
443 / TCPEncrypt web applications with TLS certificates on port 443.
Port
SFTP
22 / TCPTransfer files securely through SSH tunnels.
Port
SSH
22 / TCPManage servers remotely with encrypted shell access.
Port
SMB
445 / TCPServe file shares and authentication over TCP.
Port
HTTP
80 / TCPServe web traffic without encryption on port 80.
Port
Telnet
23 / TCPLegacy plaintext remote console access.
Port
DNS
53 / UDP / TCPProvide name resolution for infrastructure.
Port
SNMP
161/162 / UDPMonitor infrastructure with SNMP polling and traps.
Port
SIP
5060/5061 / UDP / TCP / TLSSet up VoIP signaling on SIP ports.
Port
VNC
5900 / TCPConnect to remote desktops with VNC on port 5900.
Port
RDP
3389 / TCPProvide Windows remote desktop access.
Port
NTP
123 / UDPDistribute precise time to fleet devices.
Port
ICMP
ICMP / ICMPTest reachability and latency with ICMP echo.
Port
FRP
7000 / TCPExpose internal apps through reverse tunnels.
Port
Minecraft
25565 / TCPHost multiplayer Minecraft worlds.
Port
FTP
20/21 / TCPServe classic file transfers on ports 20/21.
Port
IMAP
143 / TCPRetrieve email messages from servers.
Port
SQL
1433 / TCPExpose relational databases to applications.
FAQ
Frequently asked questions
Get clarity on how port forwarding works, how to interpret Port Checker results, and why some ISPs block certain ports.
What is port forwarding?
Port forwarding maps an external port on your router or firewall to an internal service. It enables access from the internet to devices on private networks.
Why do ISPs block common ports?
Consumer ISPs often block ports such as 25, 80, or 445 to limit malware and spam. Contact your provider about business plans if you need them opened.
How often should I recheck ports?
Verify ports after network changes, firewall updates, or security incidents. Automate recurring checks for mission-critical services.
Why do I see "closed" or "filtered" when my service is online?
External checks can be blocked by firewalls, cloud security groups, ISP filtering, geo rules, or source-IP allowlists. Verify the full path from the internet to your service and compare with an internal test.
What do open, closed, and filtered mean?
Open means the target accepted a connection on that port. Closed means the host was reachable but that port was not accepting connections. Filtered means packets were blocked or dropped by a firewall or ACL, so the exact state cannot be confirmed.
Do you store scan results or my targets?
We process the host and port you submit to run checks and keep limited technical logs for reliability and abuse prevention. See the Privacy Policy for details on retention and handling.
Does this replace production monitoring?
No. This tool is best for point-in-time diagnostics. For production systems, pair it with continuous monitoring, service health metrics, and alerting.