An ad blocker is a browser extension that prevents ads, trackers, and malware domains from loading. It works by intercepting outgoing network requests and cancelling ones that match a list of known ad and tracker domains — before any ad content downloads to your device.
How Do Ad Blockers Work?
When your browser loads a web page, it makes dozens to hundreds of network requests: the HTML of the page itself, images, stylesheets, JavaScript files, and requests to third-party services. Many of those third-party requests go to ad networks and trackers.
An ad blocker compares each outgoing URL against a list of known ad and tracker domains (called a filter list). When a match is found, the request is cancelled before it reaches the server. The ad never downloads, the tracker never receives your data, and the browser never executes the ad’s JavaScript.
This is different from extensions that download ads and then hide them. Network-level blocking means the ad data never reaches your device.
What Do Ad Blockers Block?
- Banner ads — image ads embedded in web pages
- Video ads — pre-roll and mid-roll ads on YouTube and other sites
- Pop-ups — new windows or overlays triggered by ad scripts
- Trackers — scripts that follow your behavior across sites
- Malware domains — sites used to distribute malicious software through ads (malvertising)
- Fingerprinting scripts — code that identifies your browser without cookies
Why Do Ad Blockers Make Pages Load Faster?
Commercial news pages routinely make 60-100 network requests to ad networks on a single page load. Each request adds latency. Ad scripts are often large JavaScript files that execute on your device, competing for CPU with the content you’re trying to read.
By cancelling these requests before they complete, an ad blocker reduces the number of connections your browser makes, reduces the JavaScript executed per page, and reduces the bandwidth consumed. The result is measurably faster page loads, particularly on slower connections and older hardware.
Are Ad Blockers Legal?
Yes. Ad blockers are legal. Users are under no legal obligation to view advertisements. Some websites include language in their terms of service prohibiting ad blockers, but terms of service are contractual at best — not law. There are no laws in any major jurisdiction that prohibit individuals from running software that controls what content loads in their browser.
What Are Filter Lists?
Filter lists are plain-text files containing rules that tell an ad blocker which URLs to block. The most widely used is EasyList, which contains hundreds of thousands of rules targeting known ad domains and ad URL patterns. Other lists target trackers (EasyPrivacy), malware (Peter Lowe’s Ad and tracking server list), and region-specific ads.
Ad blockers download updated filter lists periodically to keep up with new ad domains and techniques.
ProBlocker: A Free Ad Blocker for Chrome and Firefox
ProBlocker is a free, open-source ad blocker for Chrome, Firefox, Edge, Brave, Opera, and Vivaldi. It blocks YouTube ads, pop-ups, and trackers at the network level — with no Acceptable Ads, no account, and no data collection.