A while ago, Google announced that they would be removing XSLT support from Chrome, and other browser makers followed suit. That’s put us in a tight spot, because the Numbas default theme has always used XSLT to produce the displayed exam content.
On November 17th, 2026, the stable version of Chrome will disable XSLT, so any existing Numbas exam packages will stop working.
Update 2026-10-01: I’ve removed all of the XSLT code, so new Numbas exams will work without any problems on browsers without XSLT support. This is a big change for the compiler, so if you’ve written a custom theme, look at the notes for theme authors below.
Here’s how the removal of XSLT affects existing Numbas packages.
Exams loaded directly from numbas.mathcentre.ac.uk
If you link directly to the Numbas editor, for example using the “embed” link, you don’t need to do anything: I’ve added the polyfill to the default theme, and exams loaded directly from the editor always use the latest version of the code.
Exam packages uploaded to a Numbas LTI provider
I’ve written a script which will update all exam packages uploaded to a Numbas LTI provider.
Download xslt-polyfill.min.js and put it in /srv/numbas-lti-provider/numbas_lti/static.
Run python manage.py collectstatic --noinput.
Download add_xslt_polyfill.py and put it in /srv/numbas-lti-provider/numbas_lti/management/commands.
Run python manage.py add_xslt_polyfill. The script will edit each uploaded exam package so it loads the polyfill.
Standalone exam packages
Other exam packages not loaded from the editor or an LTI provider will have to be fixed individually, with the polyfill added to each package.
Bulk update script
I’ve written a Python script which will help if you have a large collection of packages on a server that you have terminal access to.
Download add_xslt_polyfill_standalone.py. When you run it, you can either give the URL of a copy of xslt-polyfill.min.js, if you want to have a single copy that all packages load, or the path to a copy of the file on the same machine, which will be copied into each package.
For safety, by default the script just prints the list of packages that it would update. Run the script with the --write option to actually update those packages.
Fixing individual packages
For each exam package, download xslt-polyfill.min.js and put it at the top level of the package (in the same directory as the index.html file)
Edit index.html and insert the following just before the </head> tag:
<script src="xslt-polyfill.min.js"></script>
Custom themes
I found 29 custom themes on numbas.mathcentre.ac.uk that override the old XSLT templates. To work with the new, XSLT-less version of Numbas, these themes would have to be rewritten.
Instead, I’ve set up a facility for these themes to ask to use the old compiler. That means that exams using those themes will still run, but will include the XSLT polyfill script. Exams using these themes won’t benefit from any future changes to the Numbas compiler.
I’ll email authors of affected themes, to offer support with removing the XSLT code.
I’m sorry about this situation – the browser makers have never removed a feature before, so this was hard to foresee. I don’t like making too many breaking changes, so didn’t remove the XSLT code when rewriting the default theme last year. This time, my hand has been forced!