Port Monitoring
Know the moment a service stops accepting connections - and the moment one you meant to keep private starts.
- Any TCP port, checked every minute, or every 5 on the free plan
- From 7 locations on 4 continents
- Alerts when a port closes, or opens
Trusted by teams at
Every service, and whether it's answering
- 1
See every service at a glance
Each port's status and connection time, in one list.
- 2
Know which service stopped
A server can answer pings while its database is down. Watching the port shows which one.
- 3
Catch what shouldn't be open
Ports that must stay private, watched from outside so you'd know the day they're exposed.
Checked from around the world
A port that's blocked on one network can be open on another. Mon tries yours from around the world, so a route that's broken somewhere doesn't go unseen.
7 locations, 4 continents
North and South America, Europe and Asia, so an outage in one region doesn't go unseen in another.
Placed for you, or by you
Mon spreads each monitor's checks itself, or you choose the locations it checks from.
Addresses you can allowlist
Every location's IP addresses are published in your account, ready for your firewall.
Every port, watched both ways
A port that stops answering takes a service down. One that starts answering can let anyone in. Mon watches for both.
Hear about it first
When a port stops accepting connections, Mon tells you straight away - and again when it's back - wherever your team will see it.
- By email, in Slack or to your own webhook
- SMS on paid plans
- Alerted only after the failed checks in a row you chose, so a blip stays quiet
Watch the ports that should stay shut
Turn a monitor around: the port is up while nothing answers from outside, and you're alerted the moment something does.
- Catch a database or cache exposed by a firewall change
- Checked from outside your network, as an attacker would see it
- Every minute on paid plans
Any service on any port
SSH, mail, databases, remote desktops, game servers - if it accepts TCP connections, Mon can watch it.
- Any port from 1 to 65535
- IPv4, IPv6, or whichever the name resolves to
- Connection time recorded on every check
Keep your users in the loop
A public status page shows how each of your services is doing, and maintenance windows keep planned work from counting against you.
- Status pages for the monitors you choose
- Maintenance windows for planned downtime
- A weekly report covering every monitor
Add a hundred in one go
Paste a list of host:port - one per line, or straight from a spreadsheet - and get a monitor for each, all with the same checks and alerts.
- Named after the host and port
- Ports you already watch are skipped
- URLs are read down to their host
Works with the tools you already use
On Enterprise plans, connect your registrar or DNS host once and Mon imports every domain it finds, picking up new ones as you buy them. On every plan, hear about them where your team already talks.
Namecheap
Every domain registered in your Namecheap account.
Amazon Route 53
Every hosted zone in your AWS account.
Azure DNS
Every DNS zone in your Azure subscription.
Slack
Reminders and alerts posted to the channel of your choice.
Everything else your site depends on
The same account, the same alerts and the same dashboard, for every other check your site needs.
- Learn more
Website monitoring
Alerts the moment a site stops answering, from 7 locations.
- Learn more
Keyword monitoring
Alerts when a page stops showing - or starts showing - the words you choose.
- Learn more
Defacement monitoring
Alerts when a page stops looking like your site, judged in a real browser.
- Learn more
SSL monitoring
Warnings 30, 15, 7 or 1 day before a certificate expires, on any port.
- Learn more
Domain expiration
Reminders before a domain lapses, and when its registrar changes.
- Learn more
Ping monitoring
Whether a server answers at all, and how quickly.
Frequently asked questions
Everything about keeping an eye on your ports.
What is port monitoring?
It is a service that connects to a port on your machine on a schedule, from outside your network, and tells you as soon as it stops accepting connections - so you hear that a database, mail server or SSH daemon has stopped before anyone who depends on it does.
Is port monitoring free?
Yes. Mon's free plan includes 5 monitors checked every 5 minutes, and each port you watch uses one. Paid plans start at 10 monitors and check as often as every minute.
How does Mon check a port?
It opens a TCP connection to the port from each of its locations, over IPv4, IPv6 or whichever the name resolves to, and times how long the connection takes. The port is up while it accepts the connection, and down when it refuses or doesn't answer in time.
Can Mon alert me when a port is open?
Yes. Tell a monitor the port should be closed, and it turns the check around: the port is up while nothing answers from outside, and you're alerted the moment it does - the way to catch a database or cache exposed to the internet by mistake.
Does Mon check UDP ports?
No - port monitors make TCP connections. For DNS, a DNS monitor checks the records a server answers with, which tells you more than whether the port is open.
How is it different from ping monitoring?
A ping tells you the machine is reachable. A port check tells you the service on it is accepting connections - a server can answer pings while its database has stopped.
Should I use a port monitor for a website?
A website monitor is the better fit: it makes the request a browser would and checks the status code and the page itself, where a port check only knows that something answered on 443.
Where are the checks made from?
From 7 locations: Virginia, New York, Dallas, California, São Paulo, Frankfurt and Singapore. Mon places each monitor's checks for you, or you can choose the locations yourself.
My firewall only lets known addresses in. What do I allow?
Mon publishes the IP addresses of every location it checks from. Find them under Locations in your account, and add them to your allowlist.
Can I add all my ports at once?
Yes. Paste a list - host:port, one per line or straight from a spreadsheet - and Mon adds a monitor for each, skipping any you already watch.
Know the moment a service stops answering
Add your ports in a minute. The first 5 are free.