Ad Blocker Test

Test your ad blocker effectiveness

HOW IT WORKS

Tracker blocking verification

TRACKER LOADING

Loading popular trackers

BLOCK CHECK

Verifying what's blocked

CATEGORIZATION

Sorting by category

RATING

Final score calculation

What Your Blocker Score Actually Means

Run any ad blocker test. Score: "Your blocker blocked 28 out of 30 known trackers. Excellent protection." Close the tab. Twenty other trackers fired during that test that weren't on the list. Your "excellent protection" caught the loud trackers and missed the quiet ones, which is roughly half the surface as of 2026. Like grading a security audit by counting locked doors while the side gate is missing entirely. The arms race between trackers and blockers ended around 2020. Defenders won the script-level battle. Trackers retreated to the server side. Now the data flows through CNAME-cloaked first-party domains, server-side Google Tag Manager relays, edge analytics that never touch the client, and Privacy-Sandbox-replacement schemes that browsers themselves embed. None of that registers on a "blocked X of 30" metric, because that metric tests the 2018 attack surface. Sections below: how the arms race actually went, why Manifest V3 weakened the strongest defense, and what protection looks like when the threat model has caught up.

How the Arms Race Played Out

A short history, because the timeline tells the story. 2002-2010 was the URL blocklist era. Adblock and AdBlock Plus shipped EasyList. The list of bad URLs grew. Trackers added new domains. List grew faster. End-state: list-based blocking caught maybe 80% of 2010 ads. Cosmetic filters arrived 2010-2015. uBlock Origin and ABP could match CSS selectors and hide elements that loaded from allowed domains. Sites couldn't lie about which selectors held the ad. This worked. The anti-adblock detection war ran from 2015 to 2018. Sites checked whether uBlock had hidden their ad slots and refused to load content unless the user disabled blocking. uBlock countered by injecting fake ad script tags that sites could see, while still blocking the actual fetch. Technically a losing arms race for sites because the cost of dodging detection was lower than the cost of detecting better. First-party tracking moved into focus around 2018-2022. Google's server-side Tag Manager arrived in 2020. Site owners proxy `googletagmanager.com` through their own subdomain like `gtm.example.com`. The tracker now looks like a first-party request. Most blockers still let those through because blocking them breaks legitimate site features. From 2022 onward we're in the server-side era. Edge analytics platforms (Akamai mPulse, Cloudflare Web Analytics, Vercel Analytics) collect data at the CDN level and ship aggregated metrics to the operator. Zero client-side scripts to block. The data still flows. Manifest V3 also landed in this period and capped extensions at 30,000 filter rules, which is below what EasyList alone needs. uBlock Origin moved to a Lite mode with degraded detection. That's the surface a 2026 blocker test is supposed to measure. Most tests measure 2018.

The Trackers a 30-Item List Doesn't Catch

A typical "blocker test" loads 30 well-known tracker URLs and checks which got blocked. Google Analytics, Facebook Pixel, Hotjar, Mixpanel, Amplitude. Useful for verifying your extension is installed. Almost useless as a privacy assessment. Categories that don't show up: **CNAME cloaking.** Sites set up DNS records pointing `analytics.theirsite.com` to `tracker.adcompany.com`. Your browser sees `analytics.theirsite.com` and treats it as first-party. Blocklists don't catch this because the visible domain is unique to that site. Firefox added DNS-resolution checks in 2021. Chrome and Safari haven't followed. Research from KU Leuven put CNAME cloaking at around 10% of all sites, closer to 25% on the top 1,000. **Server-side GTM.** Operator deploys Google's tag manager on their own server. All tracking events flow through `gtm.example.com`, a subdomain they control. Browser can't tell it apart from API requests. Estimated adoption among the Alexa top 10,000: around 18% as of late 2024. **Edge analytics.** Cloudflare and Akamai run analytics at the CDN. The page never sends a tracking script. The CDN logs the request and builds the user profile from server logs, then forwards to the analytics dashboard. Nothing to block. Fastly ships this as Compute@Edge. Vercel ships this as Vercel Analytics. None of it appears in any blocker test. **Browser-mediated tracking.** Topics API, Attribution Reporting, Privacy Sandbox successors. Chrome ships these directly in the browser, no extension can intercept them. Firefox ships PPA. The API contract is that the browser collects topical data and reports an aggregated, supposedly-anonymized version to advertisers. For blocker test purposes, this is all invisible. A test that catches 30 of 30 client-side trackers gives you the same coverage you'd have had in 2018. The other half of the modern surface isn't in the test.

The Real Protection Stack in 2026

Three layers, each catching what the others miss. DNS-level blocking handles the network layer. Pi-hole, AdGuard Home, NextDNS. Block at the resolver before any request leaves the device. Catches CNAME cloaking when configured with deep CNAME inspection (NextDNS does this by default; Pi-hole needs cdrcet's CNAME detection rules). Doesn't catch server-side analytics because the server-side tracking lives on the site's own domain. Doesn't break sites the way browser-level extensions sometimes do. Same logic as a bouncer at the front door of a club: anything without an invitation gets turned away on the threshold, never reaches the dance floor. Browser extensions cover the script and request layer. uBlock Origin remains the gold standard for Manifest V2 browsers (Firefox, Edge). uBlock Origin Lite under MV3 (Chrome) lost roughly 30% of detection capability, which most users haven't been told. Brave's built-in shields hit before the extension layer and catch some MV3-resistant cases. Browser containers handle cross-site data flow. Firefox's Total Cookie Protection isolates third-party cookies per site. Brave's strict shields, Safari's ITP, all attempt the same thing with different aggressiveness. None of them stop server-side tracking on a single site, but they stop the cross-site stitching that turns one tracker's data into a marketable profile. For server-side tracking, there is no defense at the user level. The page operator decided to track you, the data flows through their server, which they own. The only response is operator-level: don't visit sites that disrespect their visitors. Not a satisfying answer, which is why nobody writes the headline that way. The WHOX blocker test runs a full 60+ tracker probe set across categories: analytics, ads, fingerprinting, CNAME-cloaked variants, and known server-side relays. Then surfaces which categories your blocker caught and which it didn't. Useful when you want to know whether your protection is 2018-tier or 2026-tier.

FREQUENTLY ASKED QUESTIONS

What is an ad blocker?

An ad blocker is a browser extension that prevents advertising scripts, trackers, and analytics from loading on web pages.

Which blocker is best?

uBlock Origin is considered the most effective free ad blocker. Pi-hole and AdGuard are also excellent options.

Is this test safe?

Yes. We only check if trackers load, we don't collect any personal data.

All our tests

Run the full WHOX toolkit from one place: leak checks, fingerprint probes, network diagnostics, reputation lookups, and privacy failure tests.