voiddo portcheck vs portchecker.io
Both tools involve ports, but they answer completely different questions. portcheck shows what is listening on your local machine — the process name, PID, user, and bind address. portchecker.io tests whether a remote server is reachable from the public internet on a given port. Pick based on what you actually need to know.
voiddo portcheck — use when
- You need to know which process is listening on a local port — PID, command name, user
- You want to audit local services: find mystery listeners, services bound as root, unexpected daemons
- You are debugging a service that is not starting: confirm it actually bound its port
- You need to work offline or in an airgapped environment — zero network required
- You are in a CI container, VPN, or firewall-restricted environment where outbound probes fail
- You want zero external dependencies — reads directly from kernel socket tables
portchecker.io — use when
- You need to know if a remote server port is reachable from the public internet
- You just opened a firewall rule or security group and want to confirm external access
- You deployed a VPS or cloud instance and want to verify a port is accessible
- You are debugging client connectivity: client cannot connect, want to rule out firewall vs service
- You need to probe from an external IP — not from your own network or the host itself
Feature comparison
| Feature | voiddo portcheck | portchecker.io |
|---|---|---|
| Primary use case | Local process listener audit | External remote port reachability |
| Shows process/PID/user | ✓ yes — PID, command, user, address | — no (remote probe only) |
| Tests remote server reachability | — no (local only) | ✓ yes — probes from external IPs |
| Works offline / no internet | ✓ fully offline, reads kernel tables | — requires internet |
| Works in CI / containers | ✓ zero external deps, reads /proc/net | — requires outbound network |
| Works in airgapped environments | ✓ | — |
| Checks through firewalls / NAT | — only sees local bind | ✓ probes from outside your network |
| Linux support | ✓ | ✓ |
| macOS support | ✓ | ✓ |
| CLI tool | ✓ terminal-native | — web UI only |
| Web UI | — | ✓ |
| Scriptable / automatable | ✓ JSON output, pipe-friendly | — |
| No account required | ✓ | ✓ |
| No telemetry / data sent | ✓ nothing leaves the machine | port + IP sent to portchecker.io servers |
| Open source | ✓ MIT license | — proprietary |
| Free | ✓ | ✓ |
| Faster than netstat/ss | ✓ direct /proc/net read | n/a (remote TCP probe) |
Frequently asked questions
Is voiddo portcheck an alternative to portchecker.io?
voiddo portcheck and portchecker.io solve fundamentally different problems. portcheck is a local port scanner: run it on your machine and it reveals which processes are listening on each local port — showing PID, command name, user, and bind address. portchecker.io is an external port checker: give it a remote IP or domain and a port number, and it probes that port from the internet to tell you if it is reachable externally. If your question is "what is listening on my machine?", use portcheck. If your question is "can the outside world reach my server on this port?", use portchecker.io.
Does voiddo portcheck require internet access?
No. portcheck runs entirely on your local machine with zero external dependencies. On Linux it reads from
/proc/net/tcp, /proc/net/tcp6, and /proc/net/udp and cross-references /proc/[pid]/fd/ for process identity. On macOS it uses lsof or ss. No network call is made, no data is sent anywhere. portcheck also works in airgapped environments, CI containers, and VPNs where outbound traffic is restricted.Can portcheck tell me if my server is reachable from the internet?
No — that is not what portcheck does. portcheck tells you what is listening on local ports and which process owns the socket. It cannot reach through a firewall, NAT, or cloud security group to test external reachability. For external reachability testing, use portchecker.io or a similar tool that probes from outside your network. The two tools are complementary: use portcheck to confirm your service is actually bound and listening locally, then use portchecker.io to confirm it is reachable externally.
What information does portcheck show that portchecker.io does not?
portcheck shows the full process context behind each listener: PID, command/binary name, user account that owns the socket, and whether it is bound to all interfaces (0.0.0.0), localhost only (127.0.0.1), or a specific IP. This is critical for debugging runaway processes, finding mystery listeners on expected ports, auditing which services run as root, or confirming a newly started service is actually bound. portchecker.io shows only whether a remote port responds to a TCP connect — it has no visibility into processes, PIDs, users, or local bind addresses.
When should I use portchecker.io instead of portcheck?
Use portchecker.io when you need to know if a remote server or cloud instance is reachable from the public internet on a specific port — for example, after opening a firewall rule, after deploying a new service to a VPS, or when debugging why a client cannot connect to your server. portchecker.io probes from external IPs and gives you a real external-reachability result. portcheck cannot do this because it only reads local kernel socket tables and has no outbound network capability.
Is voiddo portcheck free?
Yes — portcheck is free, MIT-licensed, and open source. No account, no ads, no telemetry, no rate limits. It is part of the 50+ free developer tools at tools.voiddo.com.
Try portcheck now
Local port scanner — zero deps, offline, MIT-licensed. See exactly what is listening and which process owns it.
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