Why Webmasters Should
View Their Sites With an Ad Blocker

Ad Blockers Can Hide a Lot More Than Your Ads

We recently discovered that ad blocking software can do more than just block ads - it can also cause essential content to disappear from your webpages. What follows is a summary of what we learned:

• Which content was being blocked
• Why that content was being blocked
• How we fixed the problem so the content would be visible to all visitors, even those using ad blockers
• A guess at the size of the problem
• Our advice to other webmasters

Missing tables: This is an example of a page that includes content presented in tables, such as this mineral's physical properties and production data. Many people visit our website expecting to find this information. Unfortunately, these types of tables were disappearing from view due to a filter used by some popular ad blockers.

Viewing Our Site With An Ad Blocker

Like most webmasters who monetize their website with ads, we knew that ad blocking software was probably costing our business a lot of money - but we never had an interest in using it. Then, in early 2016, we visited our website, Geology.com, with two popular ad blockers, AdBlock and Adblock Plus.

We were not surprised to see the ads disappear, but we were extremely disappointed to see that both of these popular ad blocking programs, each used by tens of millions of people, were also hiding a lot of our content.

Geology.com has lots of information presented in tables. This includes information about mineral properties, gemstone characteristics, resource production, chemical composition of minerals, and much more. We spent countless hours producing and presenting this data - that most visitors expect to find on a site like ours - but it was invisible to visitors running AdBlock or Adblock Plus.

Thousands of people per day were visiting our site, expecting to find this information, and then leaving with the thought that we neglected to include it. That was disappointing and at the same time embarrassing.

EasyList Filters: The image above is a portion of a screenshot taken from one of the EasyList filter files. This section of the filter file causes tables of a specified width on specific domains to be blocked by ad blocking software. In some instances, content in tables of the same width might also be blocked.

Why Was Our Content Being Blocked?

Seeking more information about ad blocking, we learned that Pierre Far was launching a service, Blockmetry, to help webmasters measure the impact of ad blockers on their websites. We have known Pierre since 2010 when he provided technical assistance to Geology.com. So, we contacted Pierre and joined a beta test of Blockmetry.

Pierre investigated our hidden content problem and identified the cause. A commonly used ad blocking filter named EasyList, used by both AdBlock and Adblock Plus, was hiding any table on our site that had a background color of cccccc. Another was hiding any table with a width of 468 pixels. A few years before, some of the ads on Geology.com were in tables with these characteristics. The person who made these filters was interested in blocking a few ads and didn’t consider how their actions might impact the content across our entire website.

EasyList Filters: The image above is a portion of a screenshot taken from one of the EasyList filter files. This section of the filter file was causing tables with a certain background color on specific domains to be blocked by ad blocking software that use this filter. In some instances, content in tables of the same color will also be blocked.

How Many Visitors Have Not Seen Our Content?

The filters targeting Geology.com content have been online (according to Internet Archive) at least as far back as 2013. We don’t have information on the historic use of these filters, but based upon current ad blocking data from Pierre’s Blockmetry combined with Geology.com traffic data, we speculate that millions of pageviews may have been delivered without our full content.

It is probable that lots of other websites are losing content when they are viewed by visitors using AdBlock, Adblock Plus and any other ad blocking technology that uses the EasyList filters. Every person who runs a website should view that website using the popular ad blockers to check their impact on formatted content.

We were able to view the filter file that was blocking our content and were horrified by what it contained. Format data from an enormous number of websites was being used to block ads. Those filters might be blocking valuable content on many of these sites - just like it was blocking ours.

Based upon our experience, we believe that every webmaster should visit their website with popular ad blockers to see if the content is still intact. Some of it might be missing.

A copy of the EasyList filter from March 24, 2016 can be viewed at Internet Archive. If you search that document for "geology.com" you should find the two filter elements that were blocking our content. Search that filter for your domain, to see if your site has been targeted by name.

Making Our Content Visible to People Who Use Ad Blockers

Pierre told us that we could make our content visible to visitors using the ad blocking filters. All we had to do was change the format of the tables that contained it. That work was accomplished by scanning the entire site for every table colored with "cccccc" or sized "468" and editing them to different formats. The filter file also contains many general filtering rules that are not domain specific.

Why did we do extra work to make sure that people who block our ads can see our content, while other webmasters are banning visitors running ad blockers? Two reasons: 1) many of our visitors are students who depend upon our site; and 2) we have pride in our work and are embarrassed if people see an incomplete version of our website.

The Impact of Ad Blockers On Our Business

While using Blockmetry, we learned that ad blockers were removing about 30% of the ads intended for Geology.com. We never expected the number to be that high. If we had the revenue from those ads, we could hire another staff member and significantly increase our rate of content production. Our visitors will never see the content that another employee or hired writers could produce. If they like Geology.com now, imagine what it would be like if we had a lot more new content going up every month.

In addition, like many other businesses, we share a portion of our profits with employees. The lost revenue from 30% of our ads being removed would increase the company's profit share paid to each employee - because lost ad revenue is subtracted directly from any profit.

We Don’t Block People Who Block Our Ads

Some websites block visitors who use ad blockers or nag them with messages to whitelist their website. Our current philosophy is to not take that approach because lots of our visitors are students, visiting our website on school computers. We don’t want to block those visitors or annoy them because they have no control over the ad blocking.

At the same time, we believe that people who use ad blockers should turn them off at least occasionally when visiting their favorite sites to learn what they are missing. The ad blockers could be hiding some really important content. If important content is being blocked, notify the webmaster because they might have the ability to fix the problem.

Banned advertisers: We filter out ads that are inappropriate.

Our Ads Pass Multiple Filters Before Anybody Sees Them

We have been running websites for two decades and dislike stinky and obnoxious ads as much as anyone. We don’t use many types of ads that everyone complains about. Most of our ads are served by Google Adsense, who we think does a pretty good job of filtering the most undesirable ads. We still see a few that we don’t want on our website. When that happens we use controls that Google provides to ban all ads from that domain or block all ads from that account. We also block a few broad categories of ads that we believe are inappropriate for our audience.

Install An Ad Blocker and Learn How Many Visitors Don’t See Your Ads

If you run a website, we suggest visiting it with an ad blocker installed on your browser. That will allow you to see if your content is complete and rendering properly. Content on your website could be blocked from a huge percentage of your visitors because you have it in a table, store it in a folder with a certain name, format it to a certain size, or because someone added information that matches an element of your content to a commonly used ad block filter.

Visiting our website with an ad blocker was an excellent use of our time. If we had not done that, we would not know that lots of people were seeing our website without some of its most important content. We were then able to estimate how many pageviews were delivered without full content by installing Blockmetry. A consultation with Pierre Far taught us how our hidden content problem could be fixed. It was definitely time well spent.