Uptime monitor: know the moment your website goes down
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An uptime monitor checks your website from outside every few minutes, confirms failures with a second attempt and alerts you when the site stops answering or returns an error. It also records an uptime percentage and response time history, so you can see how reliable your hosting really is. For most websites a five-minute interval, outage confirmation and email alerts to a shared inbox are enough; shops and APIs with strict targets check every minute and add SMS or on-call alerts. monitordefend monitors uptime and response time every five minutes and alerts by email, as shown in the demo above.
- Checks every 1–5 minutes from outside your server.
- Confirms an outage before alerting, then sends an all-clear.
- Keeps uptime percentage and response time history.
Your website can go down at three in the morning, on a Sunday or in the middle of a campaign, and without monitoring you learn about it from a customer, a colleague or a drop in sales. An uptime monitor removes that delay. It is the simplest and most important form of website monitoring: a service that keeps checking whether your site answers and tells you immediately when it does not. This page explains how uptime monitoring works, which settings matter, what uptime figures really mean, how to avoid false alarms and how to choose an uptime monitor that fits your websites.
What an uptime monitor is
An uptime monitor is a service that checks whether a website, server or API is available, at regular intervals and from outside your own infrastructure. “Uptime” is the time a system works; “downtime” the time it does not. The monitor measures both and alerts you when downtime begins.
It has to run externally. A script on your own server cannot report that the server is down, and a check from inside your office network does not see problems with your hosting provider’s network or DNS. An external uptime monitor uses the same public internet as your visitors.
How uptime monitoring works
At each interval, the monitor sends a request to your URL and waits for the answer. It evaluates the HTTP status code, the response time and optionally the content. A 200 answer within the timeout counts as up. A timeout, a connection error, a DNS failure, a certificate error or a status code such as 500 or 503 counts as down.
- Every 5 minutes Request to your URL
- Evaluate Status code, time, content
- Confirm Retry before alarm
- Alert Down and back-up messages
Before alerting, a good monitor confirms the failure with a retry or from another location. Then it opens an incident, sends the alert and keeps checking. When the site answers again, it closes the incident, sends an all-clear and adds the duration to the statistics.
Choosing the check interval
The interval decides how fast you hear about an outage. With a five-minute interval, the average detection delay is about two and a half minutes plus confirmation. One-minute or 30-second intervals detect faster and are standard on paid plans. For most company websites, blogs and small shops, five minutes is a good balance; for high-revenue shops and APIs, a minute or less can be worth the price.
What uptime percentages mean
Uptime is usually shown as a percentage of a period. The differences between seemingly similar values are large: 99 % uptime allows more than seven hours of downtime per month, 99.9 % about 43 minutes and 99.99 % about four minutes. Hosting providers often promise 99.9 %, but read the terms: maintenance windows and short outages may be excluded, and compensation is usually a small credit.
Your own monitor gives you independent numbers. Keep in mind that its precision depends on the interval: with five-minute checks, an outage of two minutes may not be seen at all, and the duration of longer outages is accurate to a few minutes.
Response time monitoring
Every uptime check also measures how long the answer takes. Response time is the early warning signal of uptime monitoring: servers that slow down over days often fail later, and slow pages cost visitors and conversions even while the site is technically up. Set a threshold per site, for example two seconds, and get an alert when it is exceeded, rather than waiting for a full outage.
Avoiding false alarms
False alarms are the main reason teams stop trusting their monitoring. They come from single failed requests, very short timeouts, firewalls or bot protection that block the monitor, and maintenance work. Confirmation by a second attempt, reasonable timeouts, allowing the monitor in the firewall and pausing checks during planned maintenance keep alerts meaningful.
The site did not respond to two checks in a row. The outage started at 03:12.
- Error: connection timed out
- Last successful check: 03:07
- You will get a message when it is back
Some protection services such as web application firewalls or Cloudflare challenges block automated requests. A good uptime monitor recognises such blocks and reports them differently from a real outage.
Alert channels
Email is the universal channel and works well for small teams, especially when alerts go to a shared inbox or helpdesk. SMS, voice calls and push notifications reach people at night. Chat integrations put alerts where teams work. Webhooks and incident platforms route alerts into on-call schedules with escalation. Choose by who needs to react and how fast.
Uptime monitoring for many websites
Agencies and companies with many sites need an overview that shows at a glance which website has a problem, consistent settings for all sites and alerts routed per site or client. Look at how pricing scales: per monitor, per website or per team member, and whether additional checks such as response time or SSL are included.
Free vs. paid uptime monitors
Free uptime monitors cover a limited number of URLs, usually at five-minute intervals, with basic alerts. Self-hosted open-source monitors are free in licence but need their own server outside the monitored infrastructure. Paid plans add shorter intervals, more locations, more alert channels, longer history, team features and status pages.
Setting up an uptime monitor
Add the homepage first, using the exact address visitors use, including https and the correct hostname with or without www. Add the pages that earn money or leads as separate monitors. Choose who receives alerts and test the path once with a URL that returns an error. Allow the monitoring service’s requests in your firewall or security plugin if they get blocked, and note planned maintenance so that alerts during that time do not cause alarm.
After the first week, look at the response time history and set a threshold a good margin above the normal values. Review incidents monthly: repeated short outages at the same time of day often point to backups, cron jobs or traffic peaks.
What to do when the monitor says “down”
Open the site yourself from a mobile connection to rule out a local problem. Check the error in the alert: a timeout points to an overloaded or unreachable server, a 5xx code to the application or web server, a DNS or certificate error to the domain configuration. Look at the hosting provider’s status page, recent deployments and plugin updates. If you cannot fix it quickly, inform customers through the channels they use and contact your host with the start time and error from the alert.
Beyond uptime
A green uptime check does not mean the website works. Broken links, a failing checkout, pages that drop out of Google or an injected script all happen while the homepage answers with 200 OK. Once uptime monitoring is in place, consider which of these risks matter for your site and whether your tool covers them.
Uptime monitoring with monitordefend
monitordefend checks each website every five minutes from Germany, confirms outages with a second attempt, records uptime and response time and sends email alerts when a site goes down or gets slower than your threshold. Firewall and bot-protection blocks are reported separately and do not count as downtime. Seven further checkers cover links, sitemap, indexing, traffic, checkout, storage and security. There are no SMS, voice or status page features.
Frequently asked questions
What is an uptime monitor?
A service that checks a website or server at regular intervals from outside, alerts you when it stops responding and records uptime and response time.
How often should an uptime monitor check?
Every five minutes is enough for most websites. Shops and APIs with high availability requirements often check every minute.
What is a good uptime percentage?
99.9 % or better is a common target for business websites, which allows about 43 minutes of downtime per month.
Why does my uptime monitor report downtime when the site works?
Typical causes are firewalls or bot protection blocking the monitor, very short timeouts or regional network problems. Confirmed checks and allowing the monitor reduce such alarms.
Can I monitor uptime for free?
Yes, several uptime monitors offer free plans for a limited number of URLs, and open-source monitors can be self-hosted.
Does an uptime monitor slow down my website?
No. One request every few minutes is negligible compared with normal traffic.
What is the difference between uptime monitoring and website monitoring?
Uptime monitoring checks availability and response time. Website monitoring can also include links, SEO, checkout, security and server resources.