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Free network tool

Online TCP port checker

Check whether one public TCP port is reachable from the internet. See its resolved IP, connection time, and safe telnet-style server banner output—no port scan.

Connected tool

Check if one public TCP port is reachable.

Telnet-style output · passive banner only
Fresh verification requiredThe token is consumed after this single check, including failures.
Why is Turnstile required?

These tools contact selected systems from shared Cloudflare-hosted infrastructure, not directly from your device's IP address. Every protected request needs a fresh challenge. Cloudflare processes the verification traffic; this application keeps no request history.

About this tool

What online tcp port checker does

Use this online port checker to test whether one known public hostname or IP accepts a TCP connection on one port. The result resembles a telnet host port check and includes the remote address, elapsed time, and any short server-first greeting without turning the service into a port scanner.

How it works

After fresh Turnstile and an explicit Check TCP port click, the same-origin /port-api Worker resolves a hostname through a fixed resolver or validates an IPv4/IPv6 literal directly, rejects private or reserved addresses, attempts one bounded TCP connection, sends no bytes, waits up to one second for at most 4 KiB of server-first banner data, and closes the socket. It returns the checked address, timing, reachability, and optional bounded banner for a terminal-safe telnet-style transcript.

Common uses

When to use it

  • Check whether a public TCP port is reachable from outside your network
  • Verify one firewall or port-forwarding change for a known endpoint
  • Test SSH 22, HTTPS 443, SMTP 25 or 587, MySQL 3306, or PostgreSQL 5432 without installing telnet or netcat
  • Confirm that a public database, mail, or reverse-tunnel endpoint accepts a TCP connection

Scope

Limits to know

  • Reachable means this external Worker completed a TCP connection; it does not prove the same path works from your device
  • This proves only that a TCP connection opened; an optional server-first banner does not validate the application protocol
  • Only one public hostname or IP and one port are accepted per fresh challenge—ranges, lists, and scans are rejected
  • The tool never sends a protocol probe, so services that wait for the client will return no banner
  • A timeout cannot distinguish every firewall, routing, and service failure

Worked example

Example input and result

Enter one known public host and TCP port to receive a remote telnet-style reachability transcript after fresh verification.

Input
db.example.com:3306
Result
% telnet db.example.com 3306
Trying 203.0.113.10...
Connected to db.example.com.
Escape character is '^]'.
8.4.11
caching_sha2_password
Connection closed.

Quick answers

Online TCP port checker FAQ

How do I check whether a TCP port is open online?

Enter the public hostname or IP, enter the one known port, complete the fresh Turnstile challenge, and click Check TCP port. Reachable means the odmin.biz Worker completed a TCP connection from its external network vantage point; it does not prove application login or reachability from every location.

Is this the same as telnet host port or nc -vz?

It answers the same basic TCP-reachability question from a remote Worker. The output is formatted like telnet and may show a server-first banner, but the tool sends no bytes and offers no interactive Telnet session or netcat-style payload.

Can I test port forwarding or a firewall rule from outside?

Yes, for one explicitly entered public endpoint. A reachable result shows that the Worker could connect from outside your network; a timeout or refusal can still have several causes, and the result says nothing about private or device-local paths.

Is this a port scanner?

No. Each fresh Turnstile submission accepts exactly one public hostname or IP and one port, with bounded time and per-isolate concurrency. Port ranges, comma-separated lists, and multi-host checks are rejected.

Why is Turnstile required?

The TCP attempt originates from shared Cloudflare-hosted infrastructure rather than your device IP. Fresh verification limits anonymous abuse so the tool can remain free without registration.

What leaves my browser?

The host, port, and one-time Turnstile token transit the same-origin Worker in request memory only.

Does reachable mean MySQL or another protocol works?

No. It confirms the TCP handshake only. A server-first banner can offer a clue, but the tool sends no protocol bytes and does not authenticate or validate the application protocol.

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