What the check does
Each check sends a real request to the address you enter, the same way a browser would. It looks up the name in DNS, opens a connection, completes the encrypted handshake when the site uses HTTPS, and asks for the page. Redirects are followed one hop at a time, up to five. The result shows the final HTTP status, the time until the site answered, every redirect, how many addresses the name resolves to, the state of the security certificate and the location of the server that ran the check.
From those measurements the checker picks one of five verdicts: reachable, slow, unreachable, automated checks blocked, or status unknown. A site counts as slow when it takes longer than three seconds to answer. A site that refuses the checker with a block or a challenge is reported as blocking automated checks, because that says nothing about whether people can use it.
Where checks run from
Checks run on a cloud server network with data centres on every continent. Each check runs from a data centre in the visitor's region, such as eastern North America, western Europe, eastern Europe or Asia-Pacific, so a site answers it much as it would answer someone nearby. The result names the city of the data centre that ran the check, which is not always the closest one to you. Visitors in the US are checked from the eastern United States. Some services, especially streaming and shopping sites built for the US, refuse visitors from other countries, so a check from outside the US can show a block that US visitors never see. A single location sees the internet the way one well-connected server does; it cannot see your home network, your internet provider or a problem that affects only one country. That is the point of the check: it takes your own connection out of the picture.
What is stored about a check
For the services that have their own page on this site, the time, verdict, status code and response time of each check run from the US region are stored for up to thirty days. Those records draw the recent-checks chart on each service page, so the chart compares like with like. Checks of other addresses are not stored. Results are reused for up to 45 seconds within each region, so that many visitors checking the same site at once do not all send new requests to it.
To prevent abuse, the number of checks from one connection is limited per minute. For that limit, the visitor's address is turned into a one-way code that cannot be turned back into the address, and the counters are deleted after a few minutes. No account, cookie or tracking is needed to use the checker.
The numbers behind a check
Every verdict on this site comes from the same fixed settings. They are listed here so a result can be read exactly.
- A check gives up after 10 seconds without an answer and reports the site as unreachable.
- An answer that takes longer than 3 seconds counts as slow.
- Up to 5 redirects are followed; a sixth is reported as too many redirects.
- A result for the same address is reused for 45 seconds within each region.
- One connection can run up to 12 checks a minute.
- Checks of the services with their own page, run from the US region, are kept for 30 days to draw the recent-checks chart.
What the check cannot do
- It does not sign in, so it cannot test accounts, payments or anything behind a login.
- It does not run apps or play video, so feature-level problems inside an app can go unseen.
- It cannot check private networks, local addresses, IP addresses or non-standard ports. Those are refused on purpose.
- It shows only what was measured. There are no visitor reports, outage maps or estimates on this site.
Service pages and guides
Popular services have their own pages with a check that runs automatically when the page opens, the usual causes of trouble, the error messages people actually see and links to the service's official help channels. The service list sorts them by category, and the guides cover what to do when a check passes but a site still will not load for you.