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

Enter your server's IP address or domain followed by a colon and the port number (e.g. 1.1.1.1:80 or example.com:443) and run a TCP check. The tool attempts a TCP handshake from 50+ global nodes and reports whether each connection succeeded, was refused, or timed out.

What is the difference between a port being refused versus timing out?

A refused connection (TCP RST) means the port is actively closed — the server replied to reject the connection. A timeout means no reply was received at all, which typically indicates a firewall is silently dropping packets before they reach the server or application.

Which TCP ports can I test?

Any valid TCP port from 1 to 65535. Common examples include port 80 (HTTP), 443 (HTTPS), 22 (SSH), 25 (SMTP), 3306 (MySQL), 5432 (PostgreSQL), and 3389 (RDP). No login or special permissions required — the check only verifies whether the TCP handshake completes.

TCP Port Check for 1.1.1.1:80

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Check TCP 1.1.1.1:80

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Global TCP Port Checker & Network Connectivity Test

A TCP check attempts a three-way handshake (SYN → SYN-ACK → ACK) to a specific host and port, then measures how long it took. Unlike ping, this goes through the same firewall rules and routing policies as real application traffic. If a port accepts a TCP connection, it is open — regardless of what the application behind it does with the data.

Firewall & Routing Validation

If a port works locally but fails from external nodes, something between the internet and your server is blocking it — a cloud security group, iptables rule, upstream ISP filter, or geoblocking policy. Running the check from multiple regions at once helps identify whether the block is global or specific to certain source countries or ASNs. A timeout from all nodes usually means the port is not reachable from outside; a refused connection means the port is actively closed.

Application vs. Transport Layer

TCP checks work at layer 4, so you can test ports that have no HTTP interface — databases (MySQL 3306, PostgreSQL 5432), mail servers (SMTP 25, IMAPS 993), SSH (22), RDP (3389), or custom application ports. No credentials needed. The check only verifies whether the TCP handshake completes, not what the application does after. Pair it with a protocol-specific test if you need to verify the application layer.

Handshake Latency Analysis

The measured time is the full round-trip to complete the TCP handshake. This is typically close to the raw network latency plus a small amount of server processing time. Large differences between regions often point to suboptimal routing — traffic taking a longer path than expected — rather than a server problem. Live mode runs this check continuously for 60 seconds so you can spot intermittent connection failures that a one-time test would miss.