Online Port Scanner Tool — Check Open Ports and Network Services

What Is a Port Scanner?

A port scanner probes a host's TCP or UDP ports to determine which are open (accepting connections), closed (no service listening), or filtered (blocked by firewall). Network ports are logical endpoints — port 80 for HTTP, 443 for HTTPS, 22 for SSH, 3306 for MySQL, and so on. Knowing which ports are open is essential for network configuration, security hardening, and debugging connectivity issues.

Online port scanners run the scan from an external perspective — they see what the public internet sees. This is different from local scanning (e.g., with nmap) which checks from inside the network.

How to Use an Online Port Scanner

1. Enter the host — domain name or IP address (e.g., example.com or 192.168.1.1)
2. Select port range — scan common ports, top 100, or a specific port number.
3. Run the scan — results show each port as open, closed, or filtered.
4. Interpret results — open ports have services listening; filtered ports are blocked by firewall.
5. Take action — close unnecessary open ports or unblock required ones.

Common Port Numbers Reference

• 22 — SSH (secure shell remote access)
• 25 — SMTP (email sending)
• 53 — DNS
• 80 — HTTP
• 443 — HTTPS
• 3306 — MySQL
• 5432 — PostgreSQL
• 6379 — Redis
• 27017 — MongoDB
• 8080 — HTTP alternate / dev servers

Use Cases

Verifying Firewall Rules After Server Setup

After configuring a VPS firewall with ufw or iptables, use an online port scanner to confirm from the outside that only intended ports (80, 443, 22) are accessible and database ports (3306, 5432) are correctly blocked.

Diagnosing Connection Issues

When users report they can't connect to an API, quickly check whether the port is open from the external internet. If port 443 shows as filtered, the issue is firewall or cloud security group configuration.

Security Audits

Regularly scan your production servers to ensure no unexpected ports have been opened. An open Redis port (6379) or database port exposed to the internet is a critical security vulnerability.

Frequently Asked Questions

Is it legal to port scan a server?

Port scanning your own servers is always legal. Scanning third-party servers without authorization can be illegal in many jurisdictions and violates most terms of service. Use online port scanners only on systems you own or have explicit permission to test.

What is the difference between open, closed, and filtered ports?

Open: a service is listening and accepting connections. Closed: no service is listening but the host is reachable. Filtered: a firewall is blocking the connection — the scanner receives no response. Filtered is often the desired state for ports that should not be publicly accessible.

How do I close an open port on a Linux server?

First, find what process is using the port: lsof -i :PORT. Stop the service if unneeded, or add a firewall rule: sudo ufw deny PORT on Ubuntu. For cloud servers, also update your cloud provider's security group or firewall rules.

Can online port scanners test localhost or internal IPs?

No — online scanners only reach publicly routable addresses. To scan internal network hosts, use a local tool like nmap (nmap -p 1-1000 192.168.1.1) from within the same network.

How does port scanning differ from a vulnerability scanner?

A port scanner only checks which ports are open. A vulnerability scanner (like Nessus, OpenVAS) goes further — it identifies services running on open ports and checks them for known vulnerabilities. Port scanning is a prerequisite step in most security assessments.