What Adblockers Are and How they Work
Adblockers are tools that stop ads (and often trackers) from loading when you browse the web. Some run as browser extensions, others run as standalone apps on your computer or phone, and some work at the network/DNS level. No matter the format, most adblockers do the same core job: they look at what a page tries to load, compare it to a set of rules, then block or hide whatever matches those rules.
What an Adblocker Actually Blocks
Most online ads are not just “images on a page.” They’re a mix of:
- Network requests (calls to ad servers, tracking pixels, analytics scripts)
- Page elements (banner containers, “sponsored” boxes, popups)
- Tracking code (scripts that follow your activity across sites)
That’s why many blockers market themselves as “ad + tracker blockers,” not only ad removers.
The Brain of an Adblocker: Filter Lists
Adblockers rely on filter lists, which are basically huge collections of rules. A well-known example is EasyList, which aims to remove most ads from international websites.
A filter list rule can tell a blocker things like:
- “Block requests to this ad domain”
- “Hide this CSS selector on pages that match this pattern”
- “Allow this one exception even if the general rule matches”
Filter lists are maintained by communities and organizations, and they update constantly because ad tech changes constantly.
FYI: If your blocker suddenly “stops working” on a site, it often means the site changed its ad URLs or layout, and your filter lists need an update.
Method 1: Blocking Network Requests
This is the most powerful part of adblocking.
When a webpage loads, it requests lots of resources: scripts, images, fonts, video segments, analytics beacons, and more. Adblockers intercept or evaluate these requests and block the ones that match their rules.
For example, if a page tries to load ads.example.com/banner.js and your filter list says “block ads.example.com,” the blocker prevents that script from loading. The ad never appears because the browser never receives it.
This approach also helps privacy: if the tracker script never loads, it can’t report your activity.
Method 2: Cosmetic Filtering (Hiding Page Elements)
Sometimes a site loads the main content from the same place as the ads, or it uses tricky layouts. In those cases, adblockers also use cosmetic filtering: they hide ad containers after the page loads, usually using CSS selectors (like “hide anything that matches this class/id”).
Cosmetic filtering is also how blockers remove:
- sticky banners
- newsletter overlays
- “accept cookies” nags (in some setups)
- sponsored boxes in feeds (when selectors match)
FYI: Cosmetic filtering can make pages look broken if a site uses the same container style for both ads and real content. That’s why blockers include allowlists (site exceptions).
Method 3: Scriptlets and Anti-Tracking Tricks
Some blockers go further than “block this domain.” They also modify how certain scripts behave (for example, preventing a tracker from reading or writing specific values).
This is where blockers can reduce things like:
- tracking pixels firing
- fingerprinting scripts collecting signals
- aggressive popup logic
This area varies a lot by product and by browser rules.
Standalone Apps vs Browser Extensions
Browser extensions
Extensions usually block ads inside the browser only. They work well, they’re easy to install, and they can apply advanced cosmetic filtering and rule logic.
The catch: browsers set limits on what extensions can do. Chrome’s shift to Manifest V3 changed the extension API model and restricted some techniques adblockers used before.
Standalone adblockers (apps)
Standalone tools (like desktop apps) often work by filtering traffic at the system level. That can cover multiple browsers and, in some cases, other apps too. This is why many people prefer them when they want one solution across a device.
DNS / network-level blockers
DNS-based blockers (like network “adblocking DNS”) stop your device from resolving known ad/tracker domains. They work across many devices and apps, and they’re great for broad tracking reduction.
But DNS can’t always separate ads from content when a platform serves both from similar infrastructure. That’s one reason YouTube-style video ads can be harder for DNS-only approaches.
Why Browser Rules Matter (Manifest V2 vs V3)
A big part of “how adblockers work” depends on what browsers allow.
- Under older models (often called Manifest V2), blockers could intercept requests more flexibly.
- Manifest V3 moves more blocking into a rules-based system (often discussed around “declarative” request rules), which can limit some advanced filtering methods.
Mozilla has publicly said Firefox will keep supporting Manifest V2 extensions “for the foreseeable future,” which is why some users prefer Firefox for full-featured blocking setups.
FYI: This doesn’t mean “one browser is always best.” It means browser design choices can affect how powerful an adblocker can be.
What Happens When a Site Fights Adblockers
Some websites detect blocked ad resources or missing ad scripts, then show warnings or limit access. YouTube is a famous example of the wider trend: platforms test anti-block flows and change them over time.
I won’t share bypass steps, but the practical options are simple:
- allowlist that site,
- use the site’s paid ad-free plan,
- or accept that blocking may break sometimes.