Is my site blocked?

Internet providers block sites inside their own networks, often in their DNS, the address book that turns your domain into a server address. An uptime monitor runs in a datacenter, on a different network with its own DNS, so its test does not pass through those blocks.

Researchers who measure internet blocking from VPN servers in commercial datacenters say such servers may see less blocking than people at home run into.

Source: ICLab (Niaki et al.), IEEE Symposium on Security and Privacy 2020

Sites that were never the target get caught too:

• Spain, 2026. During football broadcasts, providers blocked server addresses linked to alleged pirate streams of the matches. Other sites shared those addresses through a CDN, a delivery network such as Cloudflare that serves many sites from the same addresses. In a single hour, blocking only 4 to 20 of these addresses was enough to disrupt more than 400,000 domains at once.
  OONI, 30 June 2026
• Italy, 2024. On the evening of Saturday 19 October 2024, Italy's anti-piracy system, Piracy Shield, blocked drive.usercontent.google.com, the address Google Drive uses for downloads, for several hours.
  Techdirt, 21 October 2024 · Il Post, 21 October 2024

Why datacenter monitors miss ISP blocks · Innocent sites caught by blocks in Europe

A check takes the address of a page and a country. It can be any https page, such as your checkout, not only your home page. You can narrow the check to one provider, or to home or mobile. A check usually takes one to two minutes. For each provider and connection type, the answer says whether its customers get your real page. We also check that the page comes with your own security certificate (the digital ID behind the padlock in the browser), not someone else's.

If the page is blocked, the answer says how:

• the provider's DNS sends visitors to a notice page, or says your site does not exist;
• the connection to your server is cut off, or goes silent and never gets an answer;
• something between your visitors and your server shows a security certificate that is not yours, so browsers usually show a security warning;
• the provider, or the CDN in front of your site, shows its own block page instead of yours.

The answer also says when it is not a block: your site is down for everyone, or your own site turned our test away, for example with bot protection or a rule that keeps out visitors from some countries.

Next to the provider answers, every check also reports on the lists and filters that can stop visitors:

• Google's list of dangerous pages;
• Chrome's rules for domains that look like a better-known one, which can trigger its "Did you mean …?" warning;
• public DNS services that filter out harmful sites, such as Quad9 and DNS4EU, which some people use instead of their provider's.

Some providers sell an optional security filter. We test Telenor's Nettvern+ in Norway through customers who have it switched on, and show those results separately, never marked more than "likely". For Vodafone's and O2's optional security filters in Germany we have not found such customers yet, so that part of the answer says "not measured".

Every answer in detail · How a check works

Google Safe Browsing keeps a list of dangerous web pages, and browsers that use it can show a red warning instead of a page on the list. The list can name a single page, such as a new login or checkout page, while your home page and your domain stay clean. Your uptime monitor stays green.

When a browser shows a red phishing warning, most people turn back. In a study of over 25 million browser warnings, Chrome users ignored about 1 in 4 malware and phishing warnings and went on to the site. Firefox users did so about 1 in 10 times.

Source: Akhawe and Felt, "Alice in Warningland", USENIX Security 2013

Every check looks up both the page and its domain in Google Web Risk, the business version of Google Safe Browsing. Through the API, a check can also open the page in real Chrome and Edge and report the warning each one shows, with a screenshot, including Microsoft SmartScreen, which Edge uses for its warnings. The free check on this site does not open browsers.

Red warnings and lost visitors

Every check runs from connections of real devices, home routers and phones, on each provider's own network. Like any connection, they sometimes drop or switch networks halfway through. When that happens, the result is thrown out and the answer says "our side failed". That never counts as a block, and once billing starts it will not be charged.

A real block repeats. We call a page blocked only when we see the block for at least 3 different customers of that provider, in at least 2 different parts of its network. For the provider answers, we look up your domain from the customer's own line, the way their phone or computer does, not from our servers. Otherwise a block in the provider's DNS would be invisible.

When we are not sure, the answer says so. Without direct proof, such as the provider's notice page, a fake DNS answer or a certificate that is not yours, we mark a block as "likely", not certain. On mobile networks we cannot ask the provider's DNS directly; we only see the answer the customer's phone got. So a DNS block on a mobile network is never marked more than "likely". The answer says "not verified" (grey, not green) when the page opened but the most important check for that country could not be done, such as the provider's DNS for Netia in the example at the top. We have not yet measured our own error rate, so we show no accuracy percentages.

How a check works, step by step

Nothing during early access. When billing starts, you will buy credits in advance:

• You are charged per answer. One answer covers one provider and one connection type, for one page.
• You pay only for three kinds of answer: it opens, it is blocked, or it is down for everyone.
• Answers are free when our side failed, the result was unclear, the provider could not be measured or your site turned our test away. If you cancel a check, the answers it has not finished yet are free too.
• Before a check runs, a free preview shows the most it can cost. Once we accept the check, its price is fixed.
• At zero balance, checks stop. There are no surprise invoices.

Prices will be published before billing starts. Pricing in detail

Tell us your site, the pages that matter most (checkout, login, landing pages) and the countries your customers are in, and we reply by email. API keys are issued by hand. There is no dashboard yet: answers, and alerts from scheduled checks, come through the API.

Get early access