Port Checker (Single Port Test)
Controlled single-target TCP port verification.
- Runs in your browser
- Free, no signup
Port Status Diagnostic
Open- Target Destination
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- Port Number
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- Standard Service
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- Response Latency
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Tests a single explicitly requested port with strict timeouts. We do not perform port scans.
Configured a new web server, SSH bastion, or database listener and need to know if the port is reachable from the outside world? Firewalls, ISP port blocks, and misconfigured bind addresses often cause connectivity problems.
This safe diagnostic tool connects to a single explicitly specified TCP port on a single host. It reports whether the port is Open, Closed, or Timed out with latency measurements.
How to use this tool
- Enter a hostname or public IP address.
- Enter a port number between 1 and 65535, or click one of the common presets (80, 443, 22, 25, 3306).
- Click Check Port to perform a controlled socket connection test.
What do Open, Closed and Timed Out mean?
Open means a service is actively listening on that port and successfully completed the TCP three-way handshake (SYN-ACK). Closed means the host is reachable, but the operating system responded with a TCP RST (reset), indicating no application is listening.
Timed Out means packets were silently dropped by a network firewall (such as AWS Security Groups, iptables, or an ISP firewall) with no response returned.
Our strict single-port safety policy
ToolDuck is a developer utility, not an offensive security scanner. We strictly forbid port scanning, CIDR sweeps, range testing, and batch service enumeration. Private network IP ranges (RFC 1918) and cloud metadata services are blocked.
Frequently asked questions
Can I test a port range (e.g. 1-1000)?
No. To protect target hosts from unauthorized scanning and comply with hosting provider terms, only a single port may be checked at a time.
Why does port 25 (SMTP) frequently time out?
Many residential ISPs and cloud providers block outbound and inbound port 25 traffic by default to curb email spam.