Uptime monitoring is the recurring check of whether a website or service responds. A tool requests a URL at fixed intervals and records whether it returned a valid response. When checks fail, it sends an alert and logs the outage.
How does uptime monitoring work?
The simplest check is an HTTP request that expects a successful status code. Further checks cover ping, ports, DNS, SSL certificate expiry and keywords on the page. Providers run the checks from several locations. Wikipedia says most services test between once per hour and once per minute, and StatusCake advertises checks every 30 seconds. According to reports, a second check from another location before the alert reduces false alarms.
Uptime is reported as a percentage of time in which the checks succeeded. The same percentage means different amounts of downtime depending on the period:
| Uptime | Downtime per 30 days | Downtime per year |
|---|---|---|
| 99% | about 7 hours 12 minutes | about 3 days 15 hours |
| 99.9% | about 43 minutes | about 8 hours 46 minutes |
| 99.99% | about 4 minutes 19 seconds | about 52 minutes |
Google’s SRE book names 99.95 percent availability as the published target of Google Compute Engine at the time of writing, which shows how such figures appear in service commitments (see SLA).
What does downtime mean for SEO?
Google’s documentation states that 5xx and 429 responses make its crawlers slow down. Already indexed URLs are kept for a while, but URLs that persistently return a server error are removed from the index. After the server recovers, Google raises the crawl rate again gradually. For an urgent shutdown of one to two days, Google suggests serving an informational page with a 503 status instead of the regular content.
| Type | What is checked? | Usual frequency | What it catches |
|---|---|---|---|
| Uptime monitoring (this term) | whether a URL is reachable and returns the expected status code within a time limit | short intervals, often minutes | Outages and server errors (5xx), including at night. On 5xx and 429, Google temporarily slows down crawling. |
| Website monitoring | Umbrella term for availability, load time and functions of a website, such as login or checkout | varies by check | broken user flows on pages that respond without errors themselves |
| Change monitoring | Content of a page or file compared with the previous fetch | set by the user | changes without an error code, such as a new title, a changed canonical or a removed text section |
| SEO monitoring | search-relevant signals of many URLs: status codes, redirects, noindex, canonicals, robots.txt, sitemaps, content | regular crawls, usually daily to weekly | a noindex after a release that visitors never see. Google drops such pages once it reads the tag while crawling. |
| Rank tracking | Position of the site for set keywords, per country, language, location and device | daily to weekly | drops for single keywords in a fixed setup. Search Console instead shows the average topmost position across all impressions. |
| robots.txt monitoring | Content, availability and status code of robots.txt | regular, interval of your choice | a new blocking rule such as Disallow: /. Google generally caches robots.txt for up to 24 hours. |
| Sitemap monitoring | Availability, format and listed URLs of XML sitemaps | regular, interval of your choice | suddenly missing URLs or whole sections. Google limits a sitemap to 50 MB (uncompressed) or 50,000 URLs. |
There is no standard for these types of monitoring. Scope, frequency and examples are based on practical experience and vary by tool. Statements about Google's behaviour (crawling on 5xx and 429, noindex, robots.txt caching, sitemap limits, position in Search Console) are backed by sources. Sources: Google Search Central: Wie sich HTTP-Statuscodes und Netzwerkfehler auf die Google Suche auswirken; Google Search Central: Indexierung mit noindex blockieren / Block indexing with noindex; Google Search Central: So interpretiert Google die robots.txt-Spezifikation; Google Search Central: Sitemap erstellen und einreichen / Build and submit a sitemap; Google Search Central: So funktioniert die Google Suche / How Google Search works; Search-Console-Hilfe: Leistungsbericht (Suche). Last checked: .
Example
A news site checks its home page every minute from four regions. At 02:14 two regions get timeouts, the third confirms, and the alert opens an incident. The outage lasted 12 minutes, which counts against a monthly target of 99.9 percent (about 43 minutes).
Common mistakes
- Checking only the home page while product or article templates fail.
- Setting intervals so long that short outages go unseen.
- Reading a high uptime percentage as proof that the content is correct.
Sources
- What is Website Monitoring? – Uptrendsuptrends.com
- Website monitoring – Wikipedia (secondary)en.wikipedia.org
- Uptime Monitoring – Pingdom (vendor page)pingdom.com
- StatusCake (vendor page)statuscake.com
- Service Level Objectives – Google SRE Booksre.google
- Pause or disable a website – Google Search Centraldevelopers.google.com
- Fix HTTP and network errors – Google Search Centraldevelopers.google.com
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