What are filters?

We know what online ads are. They don’t relate to the content of the page, they are annoying. They are designed to make us pay. If you click an ad, another website will open (and in the worst-case scenario, a malicious file can be downloaded). We know what ads are because we're human.

An ad blocker is a program. To teach an ad blocker to recognize ads, developers use a special language: the language of filtering rules.

What filtering rules look like

A rule is a line of code written with a special syntax. It might look like this:

||example.org^

Or like this:

example.org#%#//scriptlet("abort-on-property-read", "wpsite_clickable_data")

A rule can block an element on a website: for example, an ad banner. A cosmetic rule can make a website look as if it’s never contained ads.

Some rules prohibit loading ads from websites — this also saves traffic. Others, on the contrary, may prevent the program from blocking ads on a particular site.

What filters are

Usually, rules with a similar purpose are combined into one group called a filter. AdGuard has filters that block ads on websites in a certain language: English, Swedish, Chinese, and others. Annoyance filters block popups, cookie consent forms, widgets, and other irritating elements. The URL Tracking filter removes analytics tags from website addresses.

How filters are created

Filters are manually assembled from up-to-date filtering rules. Some rules can be applied to multiple websites at once, others — to one website only. That’s why there are so many people involved in creating filters: AdGuard filter developers, enthusiasts, and even regular users.

If you’ve noticed an ad that’s not blocked by AdGuard, tell us about that by following the Report incorrect blocking or Contact support button, or simply fill out the form. The developers will be able to add a new rule to one of the filters, and many other people will see even less ads.

What AdGuard filters are responsible for

There are dozens of filters built into AdGuard. They are responsible for blocking ads, trackers, and annoyances, as well as for DNS protection. Most filters are quite unnoticeable: for example, there is a separate one behind the “Block search ads” function. On the contrary, in the Browser extension and AdGuard for Mac, filters are in plain sight.

By default, AdGuard enables the Base filter and the filter that blocks ads on websites in your language. You can see the full list of AdGuard filters in our Knowledge base.

How to add and where to find third-party filters

The pre-installed AdGuard filters are usually enough to block ads, trackers, and annoyances. But you can also add other filters to customize ad blocking to your needs.

To add a new filter, enter a link to it or import it from your device — AdGuard will recognize it automatically. In the AdGuard apps for Windows and Mac, you can also “subscribe” to filters from the list.

• In AdGuard Browser extension, new filters may be added in Custom filters.
• In AdGuard for Android, it can be done under Filters in the Content blocking section.
• In AdGuard for iOS — under Safari protection.
• In AdGuard for Windows, you can do this by clicking the Add filter button in the Ad blocker section.
• In AdGuard for Mac, click the “+” button in the Filters section.

A large collection of filters is available at filterlists.com. You can search by name, description, language, and tags.

You can activate as many filters as you want. But be careful: if you enable too many, some websites may work incorrectly.

How to add your own rules

User rules also make up a filter. All AdGuard apps have a section with rules that users can add themselves. In the Browser extension, user rules are located on the settings screen. In AdGuard for Windows and Mac, they are hidden in the Filter editor.

You can add your own rules:

• Manually. Be sure you’re acquainted with the rule syntax.
• By importing them from your device. For example, if you use AdGuard on different devices and want the same ads to be blocked everywhere. Or if someone has shared their list with you.
• By blocking an element on a website. To do that, click “Block ads on this website”. In most cases, a rule will be added automatically — you don’t need to do anything else.
• By asking AdGuard filter developers to create a rule for you. If a website you’ve reported has low traffic, the developers may consider it unnecessary to update the general filters. Though, they may suggest you to add a user rule — the ads for you will be blocked.