Free · live registry data · no login
Open Port Checker
Is 25, 80, 443 or 587 open on a host?
How it works
Check which ports are open on a host
Enter a hostname and pick a port set: web (80, 443), email (25, 465, 587, 143, 993, 110, 995), common services or admin ports, or type your own list. Our server attempts a real TCP connection to each port and reports open or closed with the time it took. Use it to confirm your mail server accepts connections before changing MX records, to prove a firewall rule works, or to spot database and remote-desktop ports that should never face the internet.
Results appear here after you click Check ports.
How this works
- 1
Resolve the host
The hostname is looked up over DNS-over-HTTPS and the first IPv4 address is targeted.
- 2
Attempt each connection
Our server opens a TCP connection to every selected port with a short timeout, recording success and handshake time, then closes it.
- 3
Judge exposure
Open ports are mapped to known services and rated: expected (web, mail), worth a look (FTP, admin consoles) or dangerous (databases, RDP).
Frequently asked questions
- How do I check if port 25 is open?
- Pick the Email preset and enter your mail server's hostname. If 25 is open, other mail servers can deliver to it. Note that testing from your own computer usually fails because ISPs and cloud providers block outbound 25 to stop spam; our server tests from a network where 25 is allowed.
- What ports should be open on a web server?
- Only 80 and 443 for the public, with 80 redirecting to 443. SSH (22) is fine when limited to your IPs or key-only. Databases (3306, 5432, 27017), Redis (6379), Elasticsearch (9200) and RDP (3389) should never be reachable from the internet.
- What is the difference between closed and filtered?
- Closed means the host actively refused the connection (nothing is listening). Filtered means a firewall dropped the packets so we got no answer at all. From outside both appear as 'not open'; filtered simply takes longer to time out.
- Is it legal to scan ports?
- Checking a handful of standard ports on your own servers or on public services is normal diagnostic activity. Scanning large ranges on systems you do not own can violate terms of service and, in some countries, computer misuse laws. Use this tool on infrastructure you manage.
- The port shows open but my app still can't connect. Why?
- An open port means the TCP handshake works from our location. Your app may be blocked by its own network (corporate firewall, ISP blocking 25), the service may require TLS or authentication you are not providing, or an allowlist on the server may admit some IPs and not yours.
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