TCP port checker tools test whether a specific port is accepting connections on a remote server. This free, browser-based tool performs a real TCP handshake attempt from an external host and reports the result as Open, Closed, or Timeout, along with connection latency for open ports. Presets for common services included. No sign-up or installation needed.
Port Checker tests whether a TCP port is open and accepting connections on any host or IP address. Enter a hostname or IP, select a port number or choose from common presets (SSH 22, HTTP 80, HTTPS 443, MySQL 3306, PostgreSQL 5432, Redis 6379, MongoDB 27017, RDP 3389), and see the result in seconds: Open (green), Closed (red), or Timeout (yellow) with response time in milliseconds. The check is performed server-side by a Vercel Function using a real TCP connection, giving accurate results that reflect what remote clients actually experience. Port checking is used by system administrators to verify that services are running and accessible, by developers to debug connectivity issues between services, and by security teams to audit which ports are exposed to the internet. For the domain name behind an IP address, use DNS Lookup. To look up an IP's network details, use IP Address Lookup.
TCP port scanning and connectivity testing are essential tools for network administration and security. When a service is not reachable, the first diagnostic step is determining whether the connection is blocked at the network layer (firewall, security group, NACL) or at the application layer (service not running, wrong bind address). Port Checker establishes an actual TCP connection from an external server, replicating exactly what a remote client would experience. A "timeout" result almost always indicates a firewall or security group is silently dropping packets, rather than the service being down. If the service were down, the OS would typically send a TCP RST immediately, resulting in a "closed" result. Common port-related issues include: services that bind to 127.0.0.1 (loopback) instead of 0.0.0.0 (all interfaces), which makes them invisible to external connections; cloud security groups that need inbound rules for specific ports; and Docker containers whose port mappings need to be verified with docker ps. Security best practice is to expose only the minimum required ports to the public internet. Database ports (3306, 5432, 27017) should generally not be exposed publicly; they should be accessed through a VPN or SSH tunnel. Web applications should expose only 80 and 443; admin interfaces and development servers should be protected behind access controls or kept off public-facing ports entirely.