Port (TCP)
Is something listening on that port and accepting connections?
Opens a TCP connection to a host and port, and closes it.
Use it when
You want to know a non-HTTP service is alive: a database, SMTP, SSH, a message broker, a game server. Also the right answer whenever ICMP is blocked and Ping is therefore useless.
What to enter
| Field | Notes |
|---|---|
| Host and port | host:port, for example db.example.com:5432. |
| Timeout | How long to wait for the connection. |
Exactly when it's DOWN
- The TCP connection fails (refused, unreachable, DNS failure).
- The connection does not complete within the timeout.
What it doesn't do
It proves the port accepts connections and nothing else. There is no protocol handshake and nothing is sent. A database that accepts connections and then rejects every query looks healthy here; so does a service wedged after accepting a socket.
For an HTTP service, HTTP tells you much more. Use Port for protocols we do not speak.
Example
smtp.example.com:25 for a mail server, or redis.internal:6379 for a cache — provided our checkers can reach it. A port on a private network is not reachable from our regions; for those, a heartbeat pinged by something inside your network is the usual answer.
Alerts
Down, recovered, and latency (connect time) if you set a threshold.
Last updated 4 October 2026
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