What a WordPress theme is responsible for – and what is not.

There are countless WordPress themes – many are available for free or cheap for a flat rate around 60 €. Most WordPress themes make the same mistakes – although the WordPress theme requirements clearly specify what a theme has to do – and what not.
In addition to numerous technical specifications, there is a decisive dogma that determines whether a theme fulfills its purpose:
Separation of Concerns.
Content
What belongs in a theme?
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Separation of Concerns
Design vs. Functionality
Themes have the task of depicting the design of a website – and not the functionality. Whenever the question arises as to whether a function could also be mapped via a plugin, the probability is high that the function does not belong in the theme.
The reason: the dependence on a theme should be as minimal as possible.
A design may no longer be suitable for your company tomorrow – but the functionalities of a website should be preserved over several theme generations.
Almost every function that is therefore mapped via the theme is therefore a technical fault, which leads to the fact that the function has to be re-implemented at the latest when changing theme – usually this leads to very high migration costs.
For functions that increase the added value of a theme, however, companion plugins are recommended – via these a theme can be charged with additional functions. Good companion plugins will continue to work even if the theme is changed.
Feature Creep
Don’t be dazzled
When we carry out website relaunches, we sometimes have to laboriously grasp which functions are mapped via the previous theme – and which via plugins. The latter can usually be reused – functions that are mapped via the theme must first be captured and then usually newly developed or developed by plugins.
This leads to enormous delays and high efforts – usually the entire website has to be developed from scratch.
This extends the period from the start of the project to go live – if in the meantime, for example.B, data changes in online shops on the live website, the go-live preparation and implementation alone means several days of effort – with the right theme you can save this effort for the next relaunch.
A WordPress theme should therefore adhere to WordPress standards as much as possible, have hardly any functionalities of its own and map the necessary ones as perfectly as possible.
Almost every functionality can be mapped via plugins – so making yourself dependent on a theme is actually unnecessary. Since the introduction of the WordPress Block Editor Gutenberg, the numerous PageBuilders, such as Elementor, have also become unnecessary – thanks to Gutenberg, there is now a uniform, cross-theme standard for the content of a WordPress website.
Standards
Concentration on the essentials
Hardly any other extension is as closely interlinked with the WordPress system as a theme – it is the glue that holds a website together and ideally gives numerous configuration options for the different website areas.
Due to the fast release cycles of WordPress, theme authors already have a lot to do here to keep up – just the switch to the block editor Gutenberg was a paradigm shift and forced many theme authors to rethink if their theme should continue to be compliant with WordPress standards.
At worst, developer hours go into features you never need – and new WordPress standards are only implemented with delay or never.
When choosing a theme, also make sure that it receives permanent updates – and which areas are mentioned particularly frequently in the release notes. This can be an indication of what the developers are focusing on – WordPress standards or features that are unimportant to you.
overview
Themes vs Plugins

The strict separation of tasks – design-relevant in themes, functionality in plugins, abruptly reduces future efforts. If this is part of the website concept right from the start, the later laborious separation during a website relaunch is omitted.
Tasks of a theme
- Color Templates
- Fonts
- Templates and Styles
- Header layout
- Footer layout
- Positioning of elements, such as menus or sidebars
Tasks of plugins
- Elements such as sliders, forms or embeddings – ideally as Gutenberg blocks
- Functions such as eCommerce, tracking or interfaces
- data processing
- processes
Themes with high function density regularly lead to a feature creep, so they have so many functions combined that they are hardly maintainable – the overview is lost and it is no longer clear which components are actually needed.
At the latest at the time of the relaunch, the processes or functions of a theme must first be recorded and newly implemented.
Recommendation
The slimmer, the better

Concept errors are difficult to solve afterwards – usually only by a complex relaunch.
Opt for a WordPress theme that is as slim as possible and see a possible maintenance and migration hell in every feature that a theme offers.
At the latest at the next relaunch – and that will certainly come – you pay on it if you have decided on a WordPress theme that has led you through countless functions in a dependency.
Especially with premium themes, i.e. purchase themes that you can buy for small money, there is a real competition as to which theme offers the most functions – after all, many functions read well, you feel like you get more for the money.
Exactly then you build on sand – but a theme is not a foundation, but only a framework for presenting the functions that you should map via plugins.
With our PageSpeed 100 WordPress Theme SV100, we ask ourselves the question every day in development: what can go away. The slimmer our theme, the longer you will enjoy it.