adguardteam/dns-sde-extension

This browser extension, created by AdGuard, is a proof-of-concept that shows what happens when a website is blocked by a DNS filtering service. Normally, when a DNS blocker stops you from visiting a site, you just see a generic browser error that looks like the site is broken. This extension replaces that confusing error with a clear, custom page explaining exactly why the site was blocked. Here is how it works. When you try to visit a website, the extension watches for loading errors on the main page. If it detects that a site failed to load, it checks with the AdGuard DNS service to see if the site was intentionally blocked. If it was, the extension shows a detailed block page instead of the standard error message. The project uses Structured DNS errors, a way for DNS services to pass along readable information about why a block happened, rather than just returning a simple failure. This tool is mainly for developers, browser makers, and tech enthusiasts who want to see how Structured DNS errors could improve the web browsing experience. For example, a parent using DNS filtering to block adult content on their home network could use this to show their kids a clear message about why a site is blocked, rather than a vague technical error. It demonstrates how browsers could natively handle DNS blocks in a more user-friendly way. It is important to note that this is a demonstration project, not a finished product for everyday users. It requires manual setup in Chrome's developer mode and needs to be paired with a specific AdGuard DNS configuration. The project trades ease of use for a focused look at a specific technology, serving as a working example of what native browser support for detailed DNS blocking could look like.