wtf is urlfilter?

AdGuard's urlfilter is a tool that helps developers build ad-blocking and content-filtering features into their own applications. Instead of starting from scratch to figure out how to block ads, trackers, or unwanted content, a developer can use this library to handle the heavy lifting of interpreting filtering rules. At its core, the library reads and applies filtering rules, essentially a list of instructions that say "block requests to this domain" or "hide this element on the page." It supports the same rule syntax that AdGuard uses across its own products, which is a widely recognized standard in the ad-blocking world. This means it can process standard ad-blocking lists, hosts-file-style blocking (like mapping a domain to nowhere), and even cosmetic rules that hide page elements rather than blocking network requests. The library also includes an example of a "man-in-the-middle" proxy, which means it can sit between a user's device and the internet, inspecting and filtering traffic as it flows through. This would be useful for anyone building a custom browser, a privacy-focused networking tool, a parental control app, or a DNS-level ad blocker. For example, if a startup wanted to create a router that blocks ads for every device on a home network, this library could power the rule engine that decides what gets blocked. It gives developers access to a proven filtering system without needing to build one from scratch. The project is written in Go, a programming language known for speed and efficiency, and the README notes that memory optimization has been a focus. That said, the library is still a work in progress. Several advanced features, like scriptlet rules, HTML filtering, and certain modifiers for handling cookies or redirects, are listed as incomplete. The README also doesn't include usage instructions yet, so developers would need to dig into the code to get started.