Attention

TYPO3 v9 has reached its end-of-life September 30th, 2021 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.

You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.

Debugging

Before diving into the topic here are a few hints about debugging in TYPO3 CMS.

The TYPO3 Core provides a simple debug() (defined in EXT:core/Classes/Core/GlobalDebugFunctions.php). It wraps around \TYPO3\CMS\Core\Utility\DebugUtility::debug() and will output debug information only if it matches a set of IP addresses (defined in $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask']).

For example, the following code:

debug($_COOKIE, 'cookie');

will produce such an output:

Debug output

Typical TYPO3 debug output

In general, look at class \TYPO3\CMS\Core\Utility\DebugUtility for useful debugging tools.