Google’s Chrome browser is undergoing significant changes that affect extensions, particularly ad blockers. This shift plays into the hands of server-side Google Tag Manager (GTM), making its monetization more feasible. With an unstoppable server-side GTM in play, the necessity of a free GTM version comes into question.
What Is Chrome Manifest v3?
When you want to create a Chrome extension, you need to create a manifest.json file. This file contains metadata about the extension, such as its name, version, and permissions. This JSON file must be formatted a certain way so that Chrome can understand it. Until 2023, the latest version of the manifest file was v2.
But Google Chrome extensions had a major update in 2024, with the obligation to use Manifest v3.
According to Google, Manifest v3 will introduce stricter permissions and restrictions meant to keep users safe from past security vulnerabilities and invasive data collection. The intention is to make it harder for malicious browser extensions to hurt internet users.
This update is a major change to the way extensions work, and it is met with a lot of controversy. The main change in Manifest v3 is the removal of the webRequest API, which allowed extensions to block network requests. This change was seen as a major blow to ad blockers, as it made it much harder for them to block ads.
Differences Between Manifest v2 And v3
Basically, in Manifest v2, it was really easy to block any network request in few lines of code.
You just had to ask for the webRequest permission and you could block any request you wanted from any domain.
The following figure shows an example of a simple ad blocker extension that blocks all requests on-the-fly thanks to the webRequest API in Manifest v2:
As you can see, the extension is directly listening to all requests and blocking them if they match a certain pattern with an unlimited number of rules.
However, in Manifest v3, the webRequest API is removed and replaced by the declarativeNetRequest API. This new API is much more limited, as it only allows you to block a limited number of requests with a limited number of rules.
Much limited, but not impossible… AdBlock Plus is working on a new version of their extension limiting the number of rules and domains to block. The uBlock adblocker is following the same direction with uBlock Origin Lite.
Server-Side GTM Quick Reminder
As discussed in a previous article, server-side GTM is based on a simple request from a GA4 tag. The advantage for Google is that they can now monetize GTM, by charging for the server side processing. The only weak point of server-side GTM was that it was easy to block that GA4 request and thus block all the web analytics and media tracking.
With client-side GTM, all the websites have to call Google servers to get the GTM container. It’s generally this domain: https://www.googletagmanager.com/*. The genius with server-side GTM is that the domain to block is not a unique domain from Google.
Server-side GTM requires you to customize the domain to send the data to. Most of the time it’s a subdomain of the website itself.
Thus, for the website example.com, the server-side GTM domain could be gtm.example.com, or analytics.example.com, or data.example.com, etc.
However, as a server-side GTM request is basically a request from a GA4 tag, it follows the same structure.
Thus, you could decide to block all the requests containing collect?v=2 in the URL, you would block all the server-side GTM requests. This is what I said in a previous article, but I was wrong…
I was aware of the Manifest v3 update, I eared it could be a challenge for adblockers but I didn’t connected the dots with server-side GTM.
Server-Side GTM And Manifest v3 Implications
The problem that adblockers are facing is slightly different: they already know all the ad servers domains to block, they are just now limited in the number of rules they can use. To block server-side GTM requests, the problem is different. Basically you don’t know all the domains or subdomains to block, but you know the pattern of a GA4 request to block.
With Manifest v3 is that you can’t block requests based on a pattern anymore: you need to specify the domain to block. This is genius! Because while it’s still easy to block all client-side GTMs with Manifest v3 adding https://www.googletagmanager.com/* to the blocklist, you can’t do the same with server-side GTM.
All this conditions combined will make server-side GTM requests unblockable:
- a specific server-side GTM subdomain for any website
- the impossibility to block requests based on a pattern for Manifest v3
- a need to list a limited number of domains to block for Manifest v3
But Why Would Google Kill GTM Free Version?
Imagine you are Google, you have a TMS tool called Google Tag Manager.
Your tool is the most used TMS in the world, and it’s free.
It requires a lot of resources to maintain, and you don’t make any money from it.
And now, you have a new product called server-side GTM, that you can monetize.
It has a weak point, that is that it’s easy to block the requests to your servers and you patch this weak point with Manifest v3.
Why would you maintain a costly “free version” of GTM, when you can make money from it?
Conclusion
If you can handle the cost of server-side GTM and still use client-side GTM, you should start thinking about a migration to server side before Google kills it.
If you can’t handle the cost of server-side GTM, you should start thinking about a migration to another TMS.
There are a lot of interesting free or freemium client-side TMS such as Matomo, Piwik PRO, etc.