Safe Wave Blog
Ad Block

What an ad blocker actually blocks

Ad blockers work from lists, not judgement. That explains what they catch, what slips through, and why the occasional site breaks.

6 min read

Man browsing on a laptop at a wooden desk

An ad blocker doesn't look at a page and decide what's an ad. It compares every request the page makes against lists of known ad and tracking addresses, and refuses the ones that match. A second set of rules then hides the empty boxes left behind.

What it reliably stops

  • Display ads served from the big ad networks: banners, sidebars and in-article blocks.
  • Many trackers: the third-party scripts that follow you from site to site.
  • Pop-ups and pop-unders opened by ad scripts.
  • A share of malicious ads, which arrive through the same networks as normal ones.

What gets through

  • Sponsored posts and native ads that the site serves itself, looking like normal content.
  • First-party tracking, where the site measures you with its own code on its own domain.
  • Ads inside some apps, which a browser extension can't reach. Device-wide or DNS-level blocking covers more of these.
  • New ad sources until the lists catch up, usually within days.

The speed effect is real

A typical news page loads dozens of third-party scripts. Blocking them means fewer downloads, less work for the processor and less data used. On slower phones and mobile connections, pages often feel noticeably quicker.

When a site breaks (a video won't play, a checkout button does nothing), pause the blocker for that site, reload, and finish what you were doing. Most blockers let you allow one site permanently in two clicks.

Extension, app or network-wide?

  1. Browser extension: the most precise, because it can hide page elements. Only covers that browser.
  2. Device-wide app: covers other browsers and many apps, and often comes bundled with security tools.
  3. Network-wide, at the router or DNS: covers every device on the network, including smart TVs, but is less precise and only works at home.

For most people a device-wide blocker on phone and computer covers the bulk of it. Allow the sites you want to support, and let the lists handle the rest.