Why do I need `zend_extension = xdebug`?

You don't need to add zend_extension = xdebug, if your current full path line is already working.

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In PHP, extensions come in two types

extension = ... -> normal PHP extensions zend_extension = ... -> Zend Engine extensions (low level hooks into the PHP engine)

Xdebug is a Zend extension, so it must be loaded using zend_extension, not extension.

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What you have is correct. According to the doc, Xdebug must be loaded after OPCache. So make sure this is in order

zend_extension=opcache zend_extension="D:\...\php_xdebug.dll"

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Why does the wizard suggest it

The Xdebug Installation Wizard gives generic advice, assuming you might install via package manager or PHP already knows where Xdebug is located

So it suggests zend_extension = xdebug

That only works if The DLL/SO is in PHP's default extension directory and PHP can resolve it automatically