Ad Blocker Detector

This tool checks whether an ad blocker or content filter is active in your browser right now. It is useful when you are troubleshooting, confirming a newly installed blocker is working, or working out why a site is behaving oddly. It runs two quick, harmless checks and reports what it sees, without touching your settings.

There is no direct way to ask a browser "is an ad blocker installed", so detection relies on watching how the browser treats things blockers are known to act on.

• The bait element. A hidden decoy is created with class names such as ads, ad-banner and adsbox. Filter lists routinely hide anything with those names, so if the decoy vanishes, a blocker did it.
• The test request. The tool tries to reach a well-known ad-serving script. If the request is stopped before it completes, a network-level blocker is at work.
• The verdict. If either probe is blocked, a filter is active. The signals panel shows exactly which one fired.

Both probes are passive. Nothing is downloaded, no external script actually runs, and the decoy is removed once its visibility has been measured.

Blockers are mostly filter lists, large plain-text files of rules that say what to stop. The best known is EasyList, with EasyPrivacy covering tracking specifically; most blockers combine several. A rule can match a URL pattern, a domain, or an element on the page, and the list is updated constantly as advertisers change their delivery paths.

There are two distinct kinds of blocking, and they fail differently. Network filtering stops a request before it leaves the browser, so the ad script never loads and never sees you. Cosmetic filtering applies a CSS rule to hide an element after the page has already fetched it, so the content arrives and is simply made invisible. That difference explains a common oddity: a page that looks clean but still loads slowly, because the elements were hidden rather than never requested.

Blocking can also happen outside the page entirely, at the DNS resolver or in a VPN, which stops traffic before the browser is involved. The DNS leak test shows which resolvers your machine is actually using.

Blocker detection is inherently a game of cat and mouse, so treat the result as a strong hint rather than an absolute. Blockers differ in what they do: some only hide page elements, some only block requests, and some deliberately avoid the obvious traps to stay undetected. Filter lists also change constantly, so a probe that worked last month may pass today.

That is why this test reports each signal separately and marks a request as inconclusive if it simply timed out. A slow connection can look like a block if you only watch for failure, so the two outcomes are kept apart. If you change your blocker settings, use the re-test button to check again: the reading is only ever a snapshot of the current moment.

Understanding why detection exists helps make sense of the messages you sometimes see. The overwhelming majority of free websites, from news to tools like this one, are funded by advertising. When an ad is blocked, the site earns nothing for the visit, even though it still paid to produce and serve the content.

Some sites respond by asking blocker users to allow ads, disable the blocker, or subscribe instead. A few go further and withhold the article until the blocker is turned off. Whether that is reasonable is a matter of opinion, but the underlying issue is real: someone has to pay for the open web, and advertising has been the default answer for a long time.

Detecting the blocker is not the same as identifying you, though. The incognito detection test shows what else a page can infer about your browser state.

There is a middle path many people take. You can keep a blocker for privacy and safety, blocking intrusive trackers and malicious ads, while allowing respectful, non-tracking ads on the handful of sites you want to support. Most blockers let you allow individual sites in a couple of clicks, and many now ship with an accept-acceptable-ads setting for exactly this purpose.

If you want to check what you have installed and how it is configured, the browser extension test shows which extensions your browser is exposing to pages. That list is often incomplete, because extensions can run in modes a page cannot see, but it is a useful starting point.