Google Chrome is set to reach version 100 soon, but it looks like the release will cause some websites to no longer work. Google has begun investigating and testing solutions.

Having been around for 13 years now, Google Chrome is rapidly approaching its 100th major version. While nothing significant is set to change in the browser, Google has long been aware that Chrome 100 could cause some websites to cease functioning altogether. However, in the last few weeks, Google has found examples in the wild of sites that will break.

According to the Chromium Bug Tracker, the websites that are known to be affected are primarily those developed with Duda, a web design kit. These websites all use the same bit of code to check what version of Chrome you’re using.

Generally speaking, if a website needs to know what browser you’re using and how up-to-date it is, it will check what’s called the “User Agent string.” This is a bit of text that your browser attaches to every web connection it makes, letting the site know about itself. If you break down what the User Agent string actually says, you’ll find a great deal of cruft, most of which is there to maintain compatibility with sites from the 1990s and early 2000s.

But that’s not what’s important in this case. Let’s take a look at an example of a User Agent string for Google Chrome.

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.45 Safari/537.36

Towards the end, you can see the part we’re looking for is “Chrome/96.0.4664.45” which gives us the precise version number of the browser. However, most web developers likely only care about the major version number, which is “96” in our example.

As the User Agent string is simply text, developers need to devise a way to interpret the info to suit their needs. In the case of Duda, the devs chose to only read the first two digits after “Chrome/”. That means “Chrome/99” would be 99, but on the other hand “Chrome/100” would be seen as version 10.

The next problem is that Duda automatically blocks any version of Chrome below version 40 — which was released in 2015, if that gives some perspective. Immediately, every version of the browser after Chrome 99 would be perceived as version 10 and therefore blocked.


Update 12/28: In a statement issued by Duda, the company has made it clear that their web design toolkit was updated to address this issue “within hours” of it being reported by Google, well ahead of the scheduled release of Chrome 100. All websites made with Duda will now continue to work correctly following Chrome 100’s release.

There was an issue with faulty configured security rules which blocked the user agent header in Chrome 100. Once the issue was reported to Duda it was fixed within hours, months before the scheduled release of Chrome 100

— Danny Mann, Director of Infrastructure and DevOps at Duda

While it remains to be seen whether any other websites are affected by the same problem, it’s excellent that Duda has swiftly seen to the issue, meaning there are currently no websites that are known to break with Chrome 100. With any luck, the workarounds Google has proposed (laid out below) will not be needed at all.


One could argue that these websites are simply outdated and need to be left behind, but that goes against the spirit of the World Wide Web. In one famous example, the original Space Jam website, which was first put online in 1996, is still live and fully functional. That’s thanks in part to the previously mentioned cruft that tricks vintage websites into thinking you’re using the old-school Netscape browser. As a side note, the history of the User Agent string is a fascinating one and well worth reading.

So, if we can’t leave these websites behind, what can be done?

The first proposal — potentially of many — is to change where developers should check for the version of Chrome. For the sake of older websites, Chrome would lock the User Agent string’s first version number to 99. If a web developer wants to check for a specific version beyond that, they’ll need to look at the second set of digits.

So instead of including something like “Chrome/100.0.1234.56″, it would include “Chrome/99.100.1234.56″.

To that end, a new flag is being added to chrome://flags that will let Googlers and web developers test whether or not various sites would be affected by this change of where Chrome’s major version number is located.

Put major version in minor version position and in User-Agent

Lock the Chrome major version in the User-Agent string to 99, and force the major version number to the minor version position. This flag is a backup plan for unexpected M100 breaks.

#force-major-to-minor

However, as you may notice in the flag’s description, this solution is considered a “backup plan.” The current solution is for Google to contact individual developers about the upcoming problem with Chrome 100.

Thus far, the company has actually had some luck with this effort, as Duda was not the only web toolkit that had a problem. Until just a few days ago, all websites created through the UK-based Yell Business were also set to break with Chrome 100. With a bit of outreach from individual Googlers, Yell Business fixed the issue for its whole network.

The current hope is that Google can definitively find all of the websites across the web that would break when Chrome 100 releases and reach out to their developers about the issue. If those problems can be fixed with enough time to spare before Chrome 100’s launch in late March, then nothing will need to change for web developers at all.

Otherwise, Chrome will be adding a new piece of cruft to the ever-lengthening User Agent string.

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About the Author

Kyle Bradshaw

Kyle is an author and researcher for 9to5Google, with special interests in Made by Google products, Fuchsia, and Stadia.

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