Port Monitoring
Confirm every service port is reachable.
Web monitoring tells you whether a web server is responding. Port monitoring tells you whether every service behind it is running. Database servers, mail servers, SSH, custom application ports — NetTests probes each TCP port you configure and alerts you immediately when a service stops accepting connections.
Services can fail without taking the web server down
A web server can return 200 responses while a critical backend service — a database, a cache, a message queue — is completely unreachable. Users might see an application that appears to load correctly but fails silently when it attempts to retrieve or store data. Port monitoring checks the services your application depends on, not just the front door.
Port monitoring is also essential for infrastructure that isn't web-facing: database servers, LDAP directories, message brokers, and internal APIs that only need to be reachable from within your network. These services rarely have URL-based health checks, but a TCP port check can verify reachability with no additional configuration required.
A port can also fail partially — accepting the initial TCP connection while the service behind it hangs, times out, or returns garbage instead of the expected banner. A check that only confirms the connection succeeded misses this class of failure entirely, which is why capturing and comparing the actual service response matters as much as the connection itself.
What NetTests port monitoring checks
NetTests opens a TCP connection to each port you configure on a schedule, recording whether the connection succeeds, how long it took, and — where the service offers one — the banner returned on connect. A database, mail server, or custom application port is checked exactly the same way, with no agent or special configuration required on the target host.
Connection timing is tracked on every check, not just success or failure. A port that still accepts connections but takes noticeably longer to respond than usual is often an early sign of a service under load or heading toward failure — visible here before it actually goes down.
Alerts fire the moment a configured port stops accepting connections, reaches your configured timeout threshold, or (where a banner is expected) starts returning something unexpected — reaching your team through email, Slack, Microsoft Teams, or SMS.
Key features
TCP port checks
Verify that any TCP port — 22, 25, 443, 3306, 5432, custom — is open and accepting connections.
Service banner capture
Capture the service banner on connection to verify that the correct service is running on each port.
Connection timeout monitoring
Alert when connection time exceeds threshold — detect degraded services before they fail entirely.
Instant alerting
Receive notifications immediately when a port stops responding or becomes unreachable.
No agent required
Checks run against any reachable host and port — nothing to install on the target service.
Multi-port, multi-host
Track every service port across every host you operate from a single dashboard.
Response-time history
Every connection attempt logged with timing, so a gradually slowing service is visible before it fails outright.
Multi-channel alerts
Reach your team through email, Slack, Microsoft Teams, or SMS the moment a port stops responding.
What you'll see
A live look at connection status across your monitored ports, and the alert that fires when one stops responding.
Not ready to commit?
Try the free Port Scanner first. Find which ports are open on a host right now, then set up continuous monitoring on the ones that matter.
Try the free tool →Free port diagnostic tools
Frequently asked questions
What's the difference between port monitoring and uptime monitoring?
Uptime monitoring checks a web-facing URL over HTTP/HTTPS — the thing your users actually interact with. Port monitoring checks raw TCP connectivity to any service, web-facing or not — databases, SSH, mail servers, internal APIs. A web server can pass every uptime check while a backend port it depends on is closed, which is exactly the gap port monitoring covers.
Can port monitoring tell if the right service is running, not just that the port is open?
Yes, for services that return an identifying banner on connection — SSH and SMTP both do, for example. NetTests captures that banner on every check, so a port that's technically open but running the wrong service (a common sign of misconfiguration or a compromised host) shows up as a change rather than a silent pass.
Why would a port stop responding without the server going down?
A firewall rule change, a service crash while the host stays up, a connection-limit or resource exhaustion issue, or a security group misconfiguration after a deploy can all close a specific port while everything else on the server keeps running normally — which is why checking the specific port matters, not just whether the host responds to ping.
What ports are worth monitoring beyond the obvious web ports?
Anything your application can't function without: the database port, cache (Redis/Memcached), message queue, internal API ports, SSH for server access, and mail server ports if you run your own. If a service failing would cause a real incident, its port is worth monitoring independently of the web-facing check.
Does port monitoring work for internal, non-public services?
As long as the port is reachable from wherever the check originates, yes — internal services on a VPN or private network work the same way public-facing ones do, provided the monitoring source has network access to reach them.
Monitor every port your services depend on
NetTests probes your TCP ports on a schedule and alerts you immediately when a service stops accepting connections.
Start monitoring free →