Quick answer: Yes — our free online port scanner checks TCP ports on any IP address or hostname in seconds, directly from your browser. No download, no registration, no command line. You get real Open / Closed / Filtered results with service names. But there are two things most port scanner guides never tell you about filtered ports and firewall interpretation that can cause you to misread your results entirely — covered below.
Port Scanner Quick Reference — 2026
| Feature | Details |
|---|---|
| Tool type | TCP port scanner (SYN + connect probe modes) |
| Supported targets | IPv4 addresses, IPv6 addresses, hostnames / domain names |
| Port range options | Top 20 Common Ports · Well-Known (1–1024) · Custom range |
| Results returned | Port number, service name, Open / Closed / Filtered status |
| Scan speed | Top 20 ports: ~5 seconds · Full 1–1024: ~60–90 seconds |
| Requires installation? | No — runs entirely in browser via our scanning servers |
| External perspective | ✅ Yes — scans from outside your network, not from your machine |
| Export results | ✅ CSV download available |
What Is a Port Scanner and Why Does It Matter?
Every service running on a networked system — a web server, an SSH daemon, a database, a game server — listens for incoming connections on a specific numbered port. Ports 0–65535 exist on every networked device. Most are closed. Some are open. A handful are filtered by firewalls. A port scanner tells you exactly which is which.
This matters because open ports are your attack surface. Every open port is a door. Some of those doors should be open — port 443 for HTTPS, port 22 for SSH administration. Others absolutely shouldn't be — port 3306 exposed to the internet means your database is reachable by anyone. A port scan takes 30 seconds and immediately shows you what the internet can see on your server. That's why every security framework from PCI-DSS to ISO 27001 mandates regular port audits as a baseline control.
An online port scanner adds one critical advantage over scanning from your local machine: it scans from an external vantage point. When you run nmap from inside your office network or home, you see the internal picture. Our tool scans from our servers, which means you see exactly what an external attacker or your own users see — the real external-facing posture of your server.
How Our Port Scanner Works — Step by Step
Understanding the mechanics helps you interpret results correctly. Most guides skip this. Here's what actually happens when you hit "Scan":
Step 1 — DNS resolution: If you enter a hostname (myserver.com), our tool resolves it to its IPv4 address before scanning begins.
Step 2 — TCP SYN probe: For each port in your selected range, our scanner sends a TCP SYN packet — the first step of a TCP handshake — to the target. This is a "half-open" scan.
Step 3 — Interpret: The target's reaction to our SYN packet determines the port status. SYN-ACK reply = Open. RST reply = Closed. No reply after timeout = Filtered.
Step 4 — Service ID: Open ports are matched against the IANA registry. Port 22 → SSH, port 80 → HTTP, port 3306 → MySQL.
Step 5 — Real-time display: Results populate as each port responds — you don't wait for the entire scan to finish.
Open, Closed, Filtered — What Each Status Actually Means
This is where most guides give you a superficial answer. Let's be more precise, because the distinction between "filtered" and "closed" has real security implications that matter.
| Status | Technical Meaning | Security Implication | What to do |
|---|---|---|---|
| Open | Target returned SYN-ACK — a service is actively listening and accepted the connection initiation | A service is reachable. Could be intentional (web server) or a serious exposure (database) | Verify every open port is intentional. Investigate unexpected ones immediately. |
| Closed | Target returned RST — the host is reachable but nothing is listening on this port | The host is up. The port is idle. This is normal — not a concern. | No action required. Closed is better than filtered for non-sensitive ports. |
| Filtered | No response after timeout — a firewall or ACL is silently dropping the probe | The port may be open behind the firewall. You cannot determine open vs closed from the outside. | Check your firewall logs to confirm. For sensitive ports this is ideal — "drop" leaks no information. |
This trips up beginners constantly. When a port shows Filtered, most people assume the port is closed and protected. It is not. "Filtered" means a firewall is dropping the probe — it says nothing about whether a service is actually running behind that firewall.
A misconfigured firewall can show every port as filtered while leaving your MySQL database fully accessible to internal attackers. Filtered on a port scan ≠ the service is off. It only means the firewall is responding, not the service behind it.
The 20 Ports You Should Scan on Every Server — Full Reference
Not all ports carry equal risk. These are the ports that matter most — the ones most commonly exposed by misconfiguration.
| Port | Service | Risk Level | Should It Be Open Externally? |
|---|---|---|---|
| 21 | FTP | 🔴 High | Almost never. FTP transmits credentials in plaintext. Use SFTP (port 22) instead. |
| 22 | SSH | 🟡 Medium | Yes, for remote access — but restrict to known IPs. |
| 23 | Telnet | 🔴 Critical | Never. Telnet sends all data including passwords in plaintext. |
| 53 | DNS | 🟡 Medium | Only on intentional DNS servers. Open resolvers can be used in DDoS attacks. |
| 80 / 443 | HTTP/S | 🟢 Low | Yes — but redirect 80 to 443. Encrypt everything. |
| 445 | SMB | 🔴 Critical | Never externally. Primary ransomware entry vector (WannaCry). |
| 3306 / 5432 | SQL | 🔴 Critical | Never. Databases should only be accessible internally. |
| 3389 | RDP | 🔴 Critical | Never directly exposed. Port 3389 is the #1 ransomware entry vector. |
Power User: Command Line Port Scanning (Nmap)
While our web tool is perfect for quick external audits, advanced security engineers use Nmap (Network Mapper) for deep-dive analysis.
nmap -sS -F -T4 [target]nmap -sV -O --top-ports 20 [target]sudo nmap -sU -p 53,123,161 [target]Who Uses a Port Scanner — Real Use Cases
Security & Pentest Teams
Port scanning is phase one of every engagement. Before you can exploit anything, you need to know what's running.
SysAdmins & DevOps
After applying firewall rules, verify they worked. Confirm security group configurations in 10 seconds.
Developers
App can't connect to an API? Scan the port to separate network issues from application logic bugs.
Gamers & Homelabs
Did port forwarding work on your router? Our tool scans from outside to confirm your server is reachable.
Port Scanner Comparison — Online Tool vs Nmap vs Masscan
| Feature | Our Online Tool | Nmap | Masscan |
|---|---|---|---|
| Setup | No installation | Local Install | Local Install |
| Perspective | External (Servers) | Internal/Local | Internal/Local |
| Core Strength | Speed & Convenience | Deep Auditing | Extreme Scale |
Port Scanning vs. Vulnerability Scanning — The Distinction That Matters
These two terms are often confused, and confusing them leads to a false sense of security. Here's the precise difference:
| Tool type | What it tells you | What it doesn't tell you |
|---|---|---|
| Port scanner | Which ports are open, closed, or filtered. What services are running. | Whether those services are vulnerable to exploits. |
| Vuln scanner | Known CVEs, misconfigurations, and weak credentials. | Zero-day vulnerabilities or application-layer logic flaws. |
A port scan tells you the doors exist. A vulnerability scan checks whether the locks are broken.
Why UDP Port Scanning Isn't Available Online
You might notice our tool only scans TCP ports. This isn't an oversight — it's a fundamental constraint of how UDP works.
TCP has a defined handshake (SYN → SYN-ACK → ACK). This means a scanner can immediately tell status. UDP has no handshake.
There's no guaranteed response from an open UDP port. Accurate UDP scanning requires sending custom application-layer probes (like a DNS query to port 53) and waiting for protocol-specific responses.
For UDP scanning, you need a locally installed tool. Use Nmap: nmap -sU --top-ports 20 [target].
Pros and Cons of Online Port Scanning
What This Tool Does Well
- No installation — scan from any browser or phone
- External perspective — sees exactly what an attacker sees
- Service name detection (e.g. 3389 shows as RDP)
- Real-time results as ports respond
- Zero cost, zero sign-up required
Limitations to Know
- TCP only — no UDP scanning available online
- No OS fingerprinting or vulnerability detection
- Slower than local Nmap for massive ranges
- Single source IP might be rate-limited by some firewalls
Is Port Scanning Legal? The Full Answer
Scanning systems you own: completely legal. Cloud providers like AWS explicitly permit scanning of resources you own without prior notification.
Scanning systems you do not own: likely illegal. In the US, this constitutes unauthorized access under the CFAA (18 U.S.C. § 1030). In the UK, the Computer Misuse Act applies. Courts in multiple countries have prosecuted individuals for port scanning alone. "I was just curious" is not a legal defense.