🔌 Port Checker
Check if specific ports are open on any host. Useful for troubleshooting network connectivity.
Port status will appear here
About Network Ports
When you submit a host and port number, the tool uses Python's socket module to attempt a TCP connection to the specified endpoint. The process begins with DNS resolution — the hostname is resolved to an IP address using the system's configured DNS resolvers. Once the IP address is obtained, the tool creates a non-blocking TCP socket and initiates a three-way handshake: it sends a SYN packet to the target port and waits for a SYN-ACK response. If the target port has a service listening and the connection is accepted within the timeout period, the port is reported as open and the response time is measured. If the target actively refuses the connection by sending a RST (reset) packet, the port is reported as closed — meaning the host is reachable but no service is listening on that port. If neither response arrives before the timeout expires, the port is classified as filtered, which typically indicates a firewall is silently dropping packets to that port.
The TCP connection attempt is minimal — it only completes the transport-layer handshake without sending any application-layer data. This means the check reveals whether a port accepts connections but does not identify what service is running or what protocol it speaks. The timeout is set aggressively to ensure results are returned quickly, even when ports are filtered and no response comes. For open ports, the tool measures the round-trip time of the handshake, which provides a rough indicator of network latency between our server and the target. The tool supports the full port range from 1 to 65535, covering well-known ports (1-1023), registered ports (1024-49151), and dynamic/private ports (49152-65535). TCP is used because it provides connection-oriented communication with explicit success or failure feedback, unlike UDP which would require application-layer probing.
Common Use Cases
System administrators verify that web servers are accessible on ports 80 (HTTP) and 443 (HTTPS) after deployment, confirming that load balancers, reverse proxies, and firewalls are correctly configured. DevOps engineers check database connectivity on standard ports — 3306 for MySQL, 5432 for PostgreSQL, 6379 for Redis, 27017 for MongoDB — to troubleshoot application connection failures. Network engineers debug firewall rules by testing whether specific ports are open or blocked, helping them identify misconfigured security group rules or iptables entries. Developers deploying containerized applications verify that Docker port mappings and Kubernetes NodePort or LoadBalancer services are correctly forwarding traffic. Remote access troubleshooters check port 22 for SSH connectivity before attempting remote connections. Security teams audit their attack surface by verifying that only intended ports are accessible from the public internet.
Security & Privacy Considerations
The tool makes outbound TCP connections from our server to the target host, which means the target server will see connection attempts originating from our server's IP address, not yours. No application-layer data is transmitted beyond the TCP handshake — the connection is closed immediately after determining the port state. Results are not stored or logged. Use this tool only on hosts you own or have explicit authorization to test. Unauthorized port scanning may violate the terms of service of hosting providers, network acceptable use policies, or applicable laws in some jurisdictions. The tool performs a single-port check, not a full port scan, which keeps the activity minimal and non-intrusive. For security auditing of your own infrastructure, this tool provides a quick, non-destructive way to verify port accessibility without needing to install additional software.
Frequently Asked Questions
Q: What is the difference between open, closed, and filtered?
Open means a service is actively listening and accepting TCP connections on that port. Closed means the host is reachable but no service is bound to that port — it responded with a connection refusal. Filtered means a firewall or network device is silently dropping packets, so no response is received within the timeout period.
Q: Can I check if a port is running a specific service?
This tool only checks whether a port accepts TCP connections. To identify the actual service and protocol running on a port, use protocol-specific tools like nmap for service detection, curl for HTTP, or psql for PostgreSQL.
Q: Why does my port show as filtered?
Most likely a firewall is blocking traffic on that port. Check your cloud provider's security groups, your server's iptables or firewalld rules, and any network-level ACLs between our server and your host. Some ISPs also filter certain ports for residential connections.
Q: Can I check ports on localhost?
No, this tool connects from a remote server. To check ports on your own machine, use local tools like netstat -tlnp, ss -tlnp, or lsof -i to see which ports are listening, and curl or telnet to test connectivity.