When is port scanning legitimately useful?

Three common cases: verifying a firewall rule (is 22 actually closed from outside?), confirming a self-hosted service is reachable from the public internet, or sanity-checking that a deployment exposed exactly what you intended. Scanning servers you don't own is a different conversation, see the next question.

Is scanning random servers safe?

Legally murky and operationally risky. Many jurisdictions treat unauthorized scanning as unlawful access prep. Cloud providers (AWS, DigitalOcean, GCP) auto-block IPs that scan their address space. Always scan only hosts you own or have written permission for. Requests are rate-limited and pattern-detected to keep this tool from being used for bulk recon.

A port shows 'filtered' instead of OPEN or closed. What's the difference?

OPEN means a service accepted the TCP handshake, something is listening. Closed means the host actively refused (no service, but the host is up and replied with RST). Filtered means a firewall is dropping the probe silently, so there is no way to tell whether a service is behind it. Filtered usually points at a firewall rather than a missing service.

Why max 10 ports and 1 scan per 15 seconds?

To keep the tool useful without making it a free recon platform. The 15-second cooldown and 10-port cap make casual sweeps painful while still letting you check the handful of ports that matter. Aggressive patterns (rapid varied targets) trigger an automated block.

Can I scan a domain like example.com or just IPs?

Both. If you enter a domain, the tool resolves it to an IPv4 once and scans that IP. Resolution happens server-side and is locked to the resolved address (DNS rebinding protected, the host can't swap to a private IP mid-scan).

Free, rate-limited (1 scan per 15 seconds, max 10 ports per scan), private IPs (RFC 1918, localhost) blocked.

Network

Port Scan

Scan open ports (limited)

Input

Rapidly scan a host for open TCP ports. Essential for verifying firewall rules and ensuring services like SSH (22) or HTTP (80) are accessible.

Terminal

Console ready. Execute a command to see output...

About Port Scan

Knock on the door

Port Scanning is the art of testing which "doors" (ports) are open on a server. An open port means a service is listening and potentially vulnerable or accessible.

Common Ports

21 (FTP): File Transfer (Insecure).
22 (SSH): Secure Shell access.
80/443 (HTTP/HTTPS): Web Servers.
3306 (MySQL): Database access (Should usually be closed to the public!).

⚠️ Danger Zone

Running port scans on servers you do not own is often considered a hostile act.

ISP Bans: Many ISPs and cloud providers (AWS, DigitalOcean) detect active scanning and will null-route your IP instantly.
Legal Action: In some jurisdictions, unauthorized scanning is classified as a cyber-attack precursor.
Honeypots: You might hit a "trap" server designed to flag your IP in global blocklists, ruining your IP's reputation across the web.

How to use Port Scan

Enter the target
Domain or IPv4. The tool resolves the domain to an IP once and scans that IP.
List the ports
Comma-separated, max 10 entries. Examples: 22, 80, 443 for a typical web host, or 3306, 5432, 6379 for common databases.
Run the scan
Hit Scan Ports. Each port comes back as OPEN, closed, or filtered, with a service-name guess based on the port number.
Follow up on OPEN ports
For 80 or 443 use HTTP Headers to inspect the web service. For 443 also try SSL Checker to validate the TLS configuration.

Frequently Asked Questions

: Three common cases: verifying a firewall rule (is 22 actually closed from outside?), confirming a self-hosted service is reachable from the public internet, or sanity-checking that a deployment exposed exactly what you intended. Scanning servers you don't own is a different conversation, see the next question.
: Legally murky and operationally risky. Many jurisdictions treat unauthorized scanning as unlawful access prep. Cloud providers (AWS, DigitalOcean, GCP) auto-block IPs that scan their address space. Always scan only hosts you own or have written permission for. Requests are rate-limited and pattern-detected to keep this tool from being used for bulk recon.
: OPEN means a service accepted the TCP handshake, something is listening. Closed means the host actively refused (no service, but the host is up and replied with RST). Filtered means a firewall is dropping the probe silently, so there is no way to tell whether a service is behind it. Filtered usually points at a firewall rather than a missing service.
: To keep the tool useful without making it a free recon platform. The 15-second cooldown and 10-port cap make casual sweeps painful while still letting you check the handful of ports that matter. Aggressive patterns (rapid varied targets) trigger an automated block.
: Both. If you enter a domain, the tool resolves it to an IPv4 once and scans that IP. Resolution happens server-side and is locked to the resolved address (DNS rebinding protected, the host can't swap to a private IP mid-scan).
: Free, rate-limited (1 scan per 15 seconds, max 10 ports per scan), private IPs (RFC 1918, localhost) blocked.