Frontend link builder 

A link builder is a class that implements \TYPO3\CMS\Frontend\Typolink\TypolinkBuilderInterface and that is called when a link is rendered in the frontend.

There are link builders for every type of link. Which link to call is determined by the respective class configured in global configuration, see FE - frontend configuration.

Register a custom link builder in your extension's ext_localconf.php:

<?php

declare(strict_types=1);

use MyVendor\MyExtension\LinkHandler\MyLinkBuilder;

defined('TYPO3') or die();

$GLOBALS['TYPO3_CONF_VARS']['FE']['typolinkBuilder']['mylinkkey'] =
    MyLinkBuilder::class;

The link builders provided by the Core can be found in namespace \TYPO3\CMS\Frontend\Typolink. It is possible to also create a custom link builder.

The main method of a link builder is the function TypolinkBuilderInterface::buildLink(). It is called with with the parameter array provided by the Core link handler.

If the link can be rendered, it returns a new \TYPO3\CMS\Frontend\Typolink\LinkResult object. The actual rendering of the link depends on the context the link is rendered in (for example HTML or JSON).

If the link cannot be built it should throw a \TYPO3\CMS\Frontend\Typolink\UnableToLinkException .