Port Checker

What is Port Checker?

Port Checker is a free online tool that tests whether a specific port on a server or IP address is open or closed. Ports are virtual endpoints for network communications, and checking their status is essential for troubleshooting connectivity issues with web servers, email, databases, and other services.

Our tool includes 200+ preset ports organized by category including web servers, databases, email, gaming, IoT, network equipment (Cisco, Ubiquiti, MikroTik), VPN, DevOps, and more.

Key Features

Open or closed? What the result actually means

This checks a port from the public internet inward — the same view an attacker or a remote user has. That framing matters: "open" means reachable from outside, which is exactly what you want for a public service and exactly what you don't want for an admin one.

• Common ports and what an open result implies: 80/443 (web — should be open for a site), 22 (SSH — restrict to known IPs), 3389 (RDP — never expose to the whole internet; use a VPN), 25/587 (mail), 3306/5432 (MySQL/Postgres — should almost never be open publicly), 25565 (Minecraft), 21 (FTP — legacy, prefer SFTP).
• Port shows closed but the service is running? Work outward: is the app actually listening on that interface (not just 127.0.0.1)? Then the server firewall (ufw/iptables, Windows Firewall, or a cloud security group), then — for home networks — port forwarding on the router. The most common miss is a cloud security group that never allowed the port.
• "Is port 25 blocked by my ISP?" Many residential ISPs block outbound 25 to fight spam, which breaks self-hosted mail. If 25 is the problem, that's usually why — use a relay on 587 instead.
• Testing port forwarding. An open result here confirms the whole path (router → firewall → app) works from outside. A closed one means one link in that chain is still blocking.
• Security note: every open port is attack surface. If this reports a database or admin port open to the world, close it or firewall it to known addresses immediately.

Want to see every exposed port and service alongside SSL, DNS and headers in one report? Run the host through the full Website Check. If a web port is open but the site misbehaves, the HTTP Headers checker shows what the server actually returns.

Frequently Asked Questions

What are common port numbers?

Common ports include: 21 (FTP), 22 (SSH), 25 (SMTP), 80 (HTTP), 443 (HTTPS), 3306 (MySQL), 5432 (PostgreSQL), 3389 (RDP), 27017 (MongoDB), and 6379 (Redis).

What's the difference between open and closed ports?

An open port has a service listening and accepting connections. A closed port has no service listening. A filtered port means a firewall is blocking the connection attempt.

Why check if a port is open?

Port checking helps verify services are running, troubleshoot connection issues, test firewall configurations, and ensure security by confirming unused ports are closed.