Port Checker

About Port Checker

Open port checker tools verify in seconds whether a specific TCP port is reachable on a server. Enter a hostname and port, and this free tool runs a real TCP connection test from an external server to tell you whether the port is open, closed, or timing out. Common presets for SSH, HTTP, HTTPS, and databases included. No sign-up required.

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.

How to use Port Checker

  1. Enter a hostname or IP address (e.g. example.com or 203.0.113.1).
  2. Enter a port number or click a preset (SSH, HTTP, MySQL, etc.).
  3. Click Check Port and see Open, Closed, or Timeout with response time.

Frequently Asked Questions

What is a network port?
A port is a number (1 to 65535) that identifies a specific service or application on a networked computer. Port 80 is HTTP, port 443 is HTTPS, port 22 is SSH, and port 3306 is MySQL. When a client connects to a server, it specifies both the IP address and the port number to reach the right service.
What does "open" vs "closed" mean?
An open port means the target host accepted a TCP connection on that port, which means a service is listening and reachable. A closed port means the host responded with a TCP RST (reset), indicating nothing is listening there. A timeout means no response was received within 5 seconds, usually because a firewall is silently dropping the packets.
What are the most common port numbers?
Commonly used ports include: 21 (FTP), 22 (SSH), 25 (SMTP email), 80 (HTTP), 110 (POP3), 143 (IMAP), 443 (HTTPS), 3306 (MySQL), 5432 (PostgreSQL), 6379 (Redis), 8080 (HTTP alternative), 27017 (MongoDB), and 3389 (Windows RDP). Ports below 1024 are called well-known ports and typically require root/administrator privileges to bind.
Why would a port show as closed even if my service is running?
Several causes: a firewall (server-side, cloud security group, or network) is blocking the port; the service is bound to localhost (127.0.0.1) instead of 0.0.0.0 so it only accepts local connections; the service is running on a different port than expected; or a load balancer is not forwarding that port.
What is the difference between TCP and UDP?
TCP (Transmission Control Protocol) establishes a connection before sending data and guarantees delivery and ordering, making it suitable for HTTP, SSH, and databases. UDP (User Datagram Protocol) sends packets without a connection, trading reliability for speed, making it suitable for DNS queries, video streaming, and online gaming. This tool checks TCP ports only, as UDP port testing requires sending a protocol-specific payload.
Can I check ports on my local network?
This tool checks ports from ToolBox's servers, not from your local machine. It can reach any publicly accessible host and port. It cannot reach private IP addresses (192.168.x.x, 10.x.x.x) or services behind a firewall that blocks external access.
Is Port Checker free to use?
Yes. Port Checker is completely free on ToolBox with no sign-up, no usage limits, and no rate limiting for normal use.

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