I've found out when Developer mode is enabled with following settings

  • dev/css/merge_css_files
  • dev/css/minify_files
  • dev/js/merge_files
  • dev/js/enable_js_bundling
  • dev/js/minify_files

Magento 2 works really slow. Please explain why it is happens.

2 Answers 2


As the documentation states, its due to the static files not being materilized, but rather being generated dynamically for each requested file.

Mergin & minifying css and js files will not have an impact on this, but merely reduce a few calls per page load.


Developer mode is slow per se since it's intended to be used only for development. If you are looking for a speed boost you should be using production mode.

In this mode:

  • Symlinks to static view files are published to the pub/static directory
  • Provides verbose logging
  • Enables automatic code compilation
  • Enables enhanced debugging
  • Shows custom X-Magento-* HTTP request and response headers
  • Results in the slowest performance (because of the preceding)

Any of these features might be causing what you see and most important, merging and minifying files doesn't make much sense in this scenario because you would want to have your files fresh since you are modifying them while developing.


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