I've been in a situation similar to yours: All my sites are/were on Skylar, which I liked and for which I created lots of CSS (to make my sites individual). I have converted one of them to Cassiopeia; the results are reasonable, but without further work (override to get an off-canvas menu for mobile, some JavaScript) not really impressive.

Therefore, I tried the above-mentioned method to make Skylar compatible to J5/6. Took me about one day (although I'm not a developer). Now, my Skylar version runs on J6 without the J6 compatibility plugin enabled.

My proposal: Do it yourself!

I'm not a developer; therefore, I cannot judge how outdated the Code of Ciáran's templates is. But the overrides in the Skylar template were more or less "clean" (in terms of deprecated classes, while my Swiss college found old stuff in the overrides of Chelsea.

One thing I can promise: If you try to refactor one of Joomla51's templates, you will find considerably more than a few lines of code to change! But as I said, it took me about one workday to adapt Skylar and three extensions.


BTW: What's your username in the German Joomla forum? You might have seen that I'm pretty active there as well.

Thanks for the detailed assessment and the practical report – that's very helpful for context.

The fact that Skylar is implemented more cleanly than Chelsea also aligns with the impression gained from other feedback. The question of outdated classes and overrides is particularly difficult for non-developers to assess objectively, which makes such experiential data all the more valuable.

The effort you described (a workday for the template plus several extensions) also confirms that the need for customization with older Joomla 51 templates shouldn't be underestimated. In practice, it's rarely just "a few lines of code."

BTW: I'm not registered in the German Joomla forum, but I do read the discussions there occasionally. and I found the j51 discussion from a week ago through a Google search, which I of course read through.

I also have to emphasize that I didn't do a complete refactoring of the template, but I did just enough to get it to work under J6.

Completely refactoring the template would imply an all new directory structure, the use of namespaces, and much more. In addition, the existing overrides need to be adjusted or removed (if possible).

The effort to refactor 50+ templates would take an experienced developer a couple of months (estimated).

I deactivated the compat plugin first, forcing the error immediately (btw. in error.php ). Found the respective line in VSC. Correct and get next error.
Later I systematically went through all the to-be-replaced classes: search in VSC and correct one by one.

I've been in a situation similar to yours:
My proposal: Do it yourself!

The problem is that i have no idea which files or what to do or what to change

Hello dear J51 community,

I also had it rewritten today using the Carmen template with the help of AI, and it now runs under Joomla 6 without the Behaviour – Backward Compatibility plugin. I'm also no longer getting any errors.

Dautrich, thank you very much for your support and advice.

(Working time approx. 1.5 hours)

All the best for 2026 and good health!

Best wishes for 2026.

So what i'm doing wrong? Went to the above mentioned classes and used VSC, Changed f.i. JFactory into \Joomla\CMS\Factory and that didn't worked so i changed the whole list again into Joomla\CMS\Factory. Still getting errors like "syntax error, unexpected fully qualified name "\Joomla\CMS\Form\FormFieldTplh...", expecting identifier."

Used VSC to open folder and find/replace all files.