---
title: "Introduction"
manual: "Frontend Theme for Extension Development"
version: "1.0"
source: "Introduction/Index.rst"
rendered: "2026-09-30T14:57:50+00:00"
---

# Introduction {#introduction}

## What does it do? {#what-does-it-do}

The **Frontend Theme for Extension Development** extension provides a
TYPO3 frontend theme for development purposes. Its job is to give a TYPO3
installation a reasonable frontend to look at and to render against, without
building a site package for it first.

> [!IMPORTANT]
> The theme is not finished. What this chapter describes is what the extension
> is for; see the note at the end of this section for what it already does.

The situations it is built for, where an extension has to be seen or exercised
in a frontend rather than only in a test assertion:

-   **Extension development**, to click through what an extension actually
    outputs instead of reading the rendered HTML in a test failure.
-   **DDEV based test instances** of an extension repository, where a throwaway
    TYPO3 installation needs a frontend rendering pages, navigation and
    content elements.
-   **Acceptance tests**, which need a stable and predictable frontend to
    drive a browser against.
-   **Reproducing an issue** in a minimal installation before debugging it.

> [!WARNING]
> This is a development tool, not a production theme. It is meant to be
> required as a development dependency of an extension repository or
> installed into a disposable test instance, and it makes no promise about
> design, markup stability or upgrade paths for a live site.

> [!NOTE]
> The theme renders a page once it is enabled for a site — through its site
> set on TYPO3 v13, or through a `sys_template` record selecting the
> classic static include, which is the only way on TYPO3 v12. See
> [Configuration](../Configuration/Index.html#configuration). It covers **every classic content element**
> `EXT:frontend` registers, the eleven menu elements, the elements of
> its own, and third-party Extbase plugins, none of which requires
> `fluid_styled_content` — that extension is not a dependency here and
> the development instances do not install it. An installation that has it
> anyway enables a bridge, which keeps the rendering the theme's own — see
> [Feature: A bridge to fluid_styled_content](../Changelog/1.0/Feature-FluidStyledContentBridge.html#feature-fluid-styled-content-bridge). It ships a set of backend
> layouts, from a bare single column through two and three column grids to
> an article, a cover page and a stack of full width bands. It renders a
> main menu, a section menu and a breadcrumb, and it offers a light/dark
> appearance switch. A seeded `/styleguide` page renders the whole
> component library on one page, so the theme can be looked at without
> building content for it first — see [Feature: A styleguide page](../Changelog/1.0/Feature-Styleguide.html#feature-styleguide). This
> chapter is extended along with the implemented features.
>
> Underneath that sits the foundation: TYPO3 v12 and v13 support from one
> code base with [core version aware](#introduction-core-version-aware)
> classes, wired by the dependency injection container of the running TYPO3
> version.

## Core version aware implementations {#introduction-core-version-aware}

Code that has to differ between TYPO3 versions lives in one directory per
supported major version in the repository root — `Core12/` and
`Core13/` on this branch. Shared code — interfaces, abstract base classes
and everything that does not depend on a core version — lives in
`Classes/`.

Only the directory matching the running TYPO3 version is registered in the
dependency injection container, so a service asking for an interface always
receives the implementation matching the current core version. The mechanism
does not depend on how many versions are supported at a time: a version is
added or dropped with its directory, and the shared code stays untouched.

## Compatibility {#compatibility}

| Branch | Extension | TYPO3 | PHP |
| --- | --- | --- | --- |
| 1 | 1.x | v12.4 | 8.1 - 8.4 |
| 1 | 1.x | v13.4 | 8.2 - 8.4 |

One row per supported TYPO3 version, because the PHP ranges differ: PHP 8.1 is
supported for TYPO3 v12 only, as [`typo3/cms-core`](https://packagist.org/packages/typo3/cms-core) 13.4 requires PHP
`^8.2`. The lowest TYPO3 v12 patch level supported is **12.4.22**.

## Contributing {#contributing}

Contributions are welcome. The development setup, the quality gates and the
commit message rules are described in the `CONTRIBUTING.md` file of the
[source repository](https://github.com/sbuerk/theme-extension-development).