What Is an Ad Blocker and How Does It Work?

Ad blockers remove ads from the websites you visit. These tools scan web pages as they load and block anything that matches known ad patterns before it ever appears on your screen. The result is a cleaner, faster browsing experience with fewer distractions and less tracking.

Our ad blocker research has found that 93% of people are familiar with ad blockers, but only 66% have a good grasp of how they actually work. 

In this guide, we’ll break down exactly what an ad blocker is, how it works behind the scenes, as well as what it can and can’t block. We’ll also explore the types of tools available so you can decide whether one is right for you.

What is an ad blocker?

An ad blocker is software designed to prevent advertisements from appearing while you browse the internet. Most commonly, it comes as a browser extension, but it can also be a standalone app, a built-in browser feature, or even a network-level tool that blocks ads across all devices.

People use ad blockers to remove intrusive ads, reduce tracking, speed up page loading, and improve overall browsing comfort. While the goal is simple (fewer ads), how ad blockers achieve it is what makes them effective.

The most popular ad blockers tend to be extensions because it’s difficult for ad blocking technology to stop in-app advertisements. For that reason, we recommend using a browser extension so you can stream from your preferred browser while blocking unwanted ads.

How do ad blockers work?

There are several different types of ad-blocking software, but they all work in a similar way. When visiting a website, the ad blocker scans as it loads and looks for elements it identifies as ads.

Some websites use proprietary ad servers, making them difficult for ad blockers to detect. Ad blockers identify these native ad platforms by looking for specific CSS elements and then changing the CSS rules to prevent the ads in those elements from displaying.

With an effective ad blocker, the user will not see any advertisement that the ad-blocking software identifies. Ad blockers can remove display ads on websites, as well as other unwanted ads like pop-ups, interstitial ads, banner ads, and more. If you’re annoyed about auto-play video ads when you land on a website, a good ad blocker can also remove these from your browsing experience.

Along with blocking ads, ad blockers can also minimize or stop ad-tracking tools, which help companies with analytics, metrics, and more. Blocking these trackers can also help minimize future ads.

Filter lists: the engine behind ad blocking

At the core of every ad blocker is something called a filter list. Think of it as a constantly updated database of known ad sources. This includes ad domains, URLs, and specific page elements where ads tend to appear.

When a web page starts loading, your ad blocker checks each request against this list. If something matches (like a known ad server or tracking script), the blocker stops it before it ever downloads. That’s why ads often don’t just disappear; they never load in the first place.

The most widely used filter list is EasyList, a community-maintained project that’s updated regularly to catch new ad networks and scripts. Popular tools like uBlock Origin, AdBlock Plus, and Total Adblock rely on EasyList as their foundation.

Many ad blockers also let you add extra lists for more aggressive blocking, including regional lists or privacy-focused ones. This layered approach is what makes modern ad blockers so effective.

DNS-level blocking

Not all ad blocking happens in your browser. DNS-level ad blockers operate at the network level, blocking ads before they reach your device.

When your device tries to connect to a known ad domain, a DNS blocker simply refuses to resolve it, meaning the connection never happens. The ad server is never contacted, and the ad never loads.

This approach can block ads across all apps and devices on your network, including phones, smart TVs, and tablets. Tools like Pi-hole, NextDNS, and AdGuard Home use this method.

The tradeoff is setup complexity. Browser extensions are easier for most people, while DNS blockers offer broader coverage but require more configuration.

Tracker blocking

Ad blocking and tracker blocking are closely related, but not identical.

Many ad blockers also block tracking scripts, which are pieces of code that track your activity across websites. These trackers often come from third-party domains and are included in the same filter lists used to block ads.

By blocking these scripts, ad blockers prevent companies from collecting data about your browsing habits. However, not all blockers handle tracking equally, and some tools are specifically designed to prioritize privacy.

Knowing how ad blockers work helps clarify what they can (and can’t) actually do.

What can (and can’t) ad blockers block?

Ad blockers are powerful, but they’re not perfect. Understanding their limits helps set realistic expectations. Here’s a breakdown of the different ad types you can encounter:

Ad Type	What it is / looks like
Display ad	A static or animated image banner embedded in a web page, typically at the top, bottom, or sidebar
Pop-up ad	A new window or overlay that appears on top of the page content, requiring dismissal
Pop-under ad	Similar to a pop-up but opens behind the active browser window, discovered when the main window is closed
Interstitial ad	A full-screen ad that appears between page loads or before content plays
Pre-roll ad	A video ad that plays before the main video content begins
Mid-roll ad	A video ad that interrupts content partway through, similar to a traditional TV commercial
Banner ad	A horizontal or vertical strip ad embedded within page content, distinct from sidebar display ads
Native ad	Sponsored content styled to blend in with the surrounding editorial content
Auto-play video ad	A video ad that begins playing automatically, often with sound, when a page loads
Tracking pixel	A tiny, invisible 1x1 image embedded in a page or email that records user behavior without displaying visible content
Sponsored content	A full article or post paid for by an advertiser but formatted to resemble organic editorial

However, not all ads function the same way, so they can’t all be blocked. Here's a look at what ad blockers can and can't do:

Ad blockers can typically block

• Display ads, banner ads, interstitial ads, and pop-ups
• Pre-roll and mid-roll video ads on many websites
• Auto-play video ads
• Third-party tracking scripts and pixels
• Some malicious ads (malvertising)
• Sponsored content that uses standard ad labels

Ad blockers typically can't block

• Server-side ads (like many YouTube ads)
• Native or sponsored content blended into articles
• Ads on platforms like Facebook that are served from their own domain
• First-party analytics tools used by websites
• Ads inside mobile apps (browser extensions don’t work there)
• Advanced tracking methods like browser fingerprinting

Browser fingerprinting identifies users by their unique device and browser characteristics rather than stored data, so there's nothing for a filter list to intercept. You can use a privacy tool like the Electronic Frontier Foundation's Cover Your Tracks to find out how unique your browser fingerprint is. 

Ad blockers may not be able to stop it all, but even partial blocking can significantly reduce the number of ads and trackers you encounter.

Ad-blocking software options

There are several different options if you’re looking to block ads while browsing the web. We've tested 20+ ad blockers using a consistent process that evaluates blocking performance, value, features, and real-world usability. See our full ad blocker testing methodology for details. 

There are browser extensions, virtual private networks (VPNs), and other blocking software that can help you. Some web browsers also have minimal ad-blocking technology built in.

Browser extensions

Browser extensions are one solution if you’re looking for an ad blocker. However, the efficiency of the ad blocker extension depends on the browser.

• Google Chrome has become more restrictive due to its transition to Manifest V3, which limits the effectiveness of some ad blockers like uBlock Origin.
• Mozilla Firefox allows browser extensions to block ads more effectively.
• Safari can block pop-up ads natively, but additional blocking requires third-party extensions from the App Store.

The best-rated ad blocker extension we’ve tested is Total Adblock, which has consistently blocked ads across browsers and performed well in repeated in-house testing. 

Built-in browser ad blockers

Some internet browsers include at least partial ad-blocking functionality. Built-in blockers usually limit only the most intrusive ads rather than preventing all ad types from displaying.

Examples include:

• Opera
• Brave
• UR Browser
• Epic Browser

VPNs

Another option for blocking ads is to use a virtual private network (VPN). A VPN doesn’t automatically block ads, but many offer built-in ad-blocking features.

For example, tools like NordVPN Threat Protection combine privacy protection with ad blocking. A VPN also encrypts your connection and hides your IP address.

If you want to protect your online browsing privacy while also saving your eyes from annoying ads, the best VPN and ad blocker combo we’ve tested is Surfshark CleanWeb. 

Ad blockers for mobile devices

Mobile devices can also use ad blockers through apps or built-in features.

Explore:

• Best ad blockers for Android
• Best ad blockers for iPhone

For a full comparison across platforms, see our roundup of the best ad blockers.

Pros of using an ad blocker

Ad blockers can do more than just streamline your browsing experience. According to our ad blocker report, 67% of ad blocker users have skipped content or stopped visiting a site altogether because of ads. Top reasons for using an ad blocker include saving data, protecting against malware, and blocking inappropriate ads.

Less internet usage

Every ad in your browser requires data to load. By using an ad blocker, you can minimize the amount of unnecessary data being used when surfing the web and improve your page loading times. If you have a data cap or use a mobile data plan, this can help minimize overages. We've found that 43% of ad blocker users cite speed as a reason for using one.

Minimize malware and phishing

Display ads on websites are an easy way for scammers to get you to click an unsafe link. By blocking ads, those adware links are less likely to reach your browser. We also found that 59% of people use ad blockers specifically for malware protection, compared to 54% for privacy. 

Safer browsing experience

Another benefit to using an ad blocker is a safer browsing experience for younger users. Although display ads on websites are vetted by Google or other ad companies, it doesn’t mean they’re appropriate for all audiences. If you’re worried about the content your kids or others may see while browsing online, blocking ads is one way to alleviate that concern.

Cons of using an ad blocker

While ad blocking can be very useful, it does come with a few downsides.

Ad blocking can break websites

Some websites are designed with ad elements in mind. This means there are designated spaces for ads to show up. If the ads in those spaces are removed, it can leave blank areas or change the web page formatting. While this might be preferable to seeing ads, the web page may not work as intended.

Websites rely on ad revenue

Most websites, from social media to blog posts, rely on ad revenue to keep going. If you’re a fan of a certain page, consider turning off the ad blocker to give them some extra support. 

Some ad blockers, like AdBlock Plus, offer an "acceptable ads" program that allows non-intrusive ads from paying advertisers to pass through by default. Once you add your favorite creators to your "allow list," then they can get paid. 

Similarly, you can use an ad blocker's whitelisting feature to manually allow specific sites you choose. 

Some web pages detect ad blockers

Many websites are caught in a never-ending war to stop ad blockers. YouTube is the biggest example of this, making it necessary to continuously retest the best YouTube ad blockers. These websites figure out how to detect and block you from using the site if you’re running an ad blocker. Even if they don’t block you outright, a lot of them send pop-ups to tell you to turn it off.

Are ad blockers safe?

Using an ad blocker is safe, as long as you’re using a trustworthy service. As with anything you sign up for, you should always make sure you’re getting ad-blocking software from a legitimate source. If you’re using an extension, make sure to check the reviews and ratings to see whether the service is good.

According to our ad blocker research, 70% of paid users say their ad blocker is completely or very effective vs. 57% of free users. 

You also shouldn’t get too complacent. Just because the annoying ads are gone (and the malicious scripts are blocked) doesn’t mean you’re safe from malware from other sources. Ad blocking won’t protect you from phishing scams or malicious downloaded files. Always make sure the web page you’re visiting is a trusted one.

Watch for red flags such as excessive permissions, unknown developers, or a lack of updates. Some fake ad blockers exist and may actually collect your data.

There’s also a privacy paradox: some free tools monetize by selling user data. Look for transparent, well-reviewed options with clear privacy policies, especially open-source tools like uBlock Origin.

Overall, sticking to reputable extensions means ad blockers are generally safe and can offer meaningful privacy benefits.

Bottom line

There are many different types of ad blockers that could reduce the number of ads and trackers you encounter online, improving both speed and privacy. Whether you’re using a built-in ad limiter like the one in Google Chrome or a dedicated ad-blocking tool, you may notice fewer of the ads that typically interrupt your browsing experience. However, no ad blocker catches everything. If you’re streaming shows or watching YouTube, some embedded ads aren’t always avoidable, so learning how to block YouTube ads might still be helpful.

For most people, starting with a browser extension like uBlock Origin or Total Adblock is the easiest option. From there, you can explore more advanced tools depending on your needs.

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