Jon Fletcher 2020-10-15

Ad-shaming: Chrome to block heavy ads

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In any war on latency, the first victim is always the ads. Users don't want them. If they have to be there, they need to make as little impact on the experience as possible. As part of this war on bad experiences, Google has recently started blocking ads that use too many resources. 

The motivation behind the block is fairly simple. These ads don't add much to publishers, or Google, but they can destroy the user experience. 

Announced in their Chromium blog, Google stated that 'a fraction of a percent of ads consume a disproportionate share of device resources, such as battery and network data, without the user knowing about it.'. The reasoning is that these ads are simply poorly programmed, or unoptimized for network usage and can be done better. The blocking started in August but publishers may only just be starting to feel the effects now. 

An ad will get blocked by the browser if the user doesn't interact with it (if the user clicks the ad, it will remain shown) and: 
  • It occupies the main thread for more than 60 seconds, total 
  • It occupies the main thread for more than 15 seconds in any 30 second period 
  • It uses more than 4 megabytes of network bandwidth 

This suggests the filter will primarily affect video ads. In place of the filtered ad will be a gray square, with the label "ad removed."


This screenshot originally appeared in the subreddit called 'Anti Asshole Design', a forum to praise user-first design features, suggesting users generally approve of the move. 

How many ads will be affected by the Chrome block? 

Chrome has said only around 0.3% of ads exceeded the “heavy ads” threshold in May. But, this is Google. 0.3% of around 65% of the entire ad market share is still a substantial amount. Worth checking for any publishers running video ads. 

What is possibly more remarkable is that while only 0.3% of ads are considered heavy, they account for 27% of network data used by ads and 28% of all ad CPU usage. 

The Chrome heavy ads update won't disrupt the majority of text and image ads. What it will do, according to Harry Kargman, CEO of ad tech firm Kargo is “hurt all the less sophisticated more invasive players who have large ad payloads and haven't done a lot of optimization - mostly the in-ad gaming providers. "

The update is designed to stop a very small percentage of ads that have a disproportionate share of the CPU power. It's not going to be a change that rocks the publishing industry to its core.

Test to see if you're affected by the block

Yet, it's always nice to be assured that your page is unaffected. And, in Chrome 84 and upwards it is possible to enable and disable the block so you can see which ads are affected. 
  • Enable chrome: // flags / # enable-heavy-ad-intervention 
  • Disable chrome: // flags / # heavy-ad-privacy-mitigations 

By default, there will be some variability added to protect user privacy. Setting chrome to Disabled prevents this, meaning the restrictions are applied deterministically, purely according to the limits. 

This should make debugging and testing easier. Run your pages with the block enabled and disabled to see if there are any major variations.


What should you do if your ads are removed by Chrome? 

There is no other penalty from Google than removing the ads so you don't need to worry about a major impact from this change. If ads are getting blocked, obviously you would lose the revenue from that ad, and it's not an ideal user experience to have a square ad-shaming you for your users to see. 

If you are having numerous ads blocked, you may want to contact your ad networks to ensure they start to run ads that use fewer resources. You can also add the Reporting API which will give you notifications when an ad is blocked via POST request to a reporting endpoint or within your JavaScript. 

Bad ads are bad for publishers 

Despite the somewhat abrupt nature of the move, for publishers, this is a positive move. If networks are serving the sort of ads that will be blocked, these ads would almost certainly be costing you readers. 

By limiting the heaviest kind of ads, we are moving closer to a balance between content and advertising that users can live with and don't have to resort to blanket measures such as adblocking.

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