ResourceLoader is the delivery system in MediaWiki for JavaScript, CSS, interface icons, and localisation text. It was first deployed to Wikipedia in 2011 and released later that year as part of MediaWiki 1.17.

It is responsible for MediaWiki's low-cost high-performant front end, built on three principles that enable quick deployment of new code seen by Web clients on all pages in less than 5 minutes.

About ResourceLoaderEdit

The page loading process for MediaWiki.
See ResourceLoader/Architecture to learn about the system's principles and overall design.

ResourceLoader was created in 2010 by Roan Kattouw, Trevor Parscal, and Timo Tijhof.

ResourceLoader loads script and style resources on-demand and only for browsers that are capable of running them. Some highlighted features:

  • Minifying and concatenating
    → This reduces the size of the code, saving bandwidth cost and download time.
    Both JavaScript files, CSS files and interface messages are loaded in a single request.
  • Batch loading and local cache defragmentation
    → This reduces the number of requests made.
    The server can provide multiple module bundles in response to a single request from the browser. These are unpacked in the browser and can be re-used from the cache on subsequent page views even if they need a different set of modules
  • Bundle static files with generated data and virtual files
    → This allow granular configuration without overhead of additional API requests. A module can contain static files but also generated data from PHP, and virtual files that represent source code from an external source (e.g. a wiki page).


  • Architecture – overview of ResourceLoader's architecture and how its features work.
  • Developing with ResourceLoader – how to create, register and load modules in MediaWiki core and extensions.
  • Core modules – documentation for of all built-in modules that ship with MediaWiki core.
  • Package modules – How to use ResourceLoader with packageFiles.


Creative Techniques for Loading Web Pages Faster
Event: Linux Conf Australia 2012 (2012-01-17)
Duration: 00:47:01
Links: videoslides

General overview and introduction for ResourceLoader.

Low-hanging fruit vs. micro-optimization
Event: OSCON 2011 (2011-07-29)
Duration: 00:35:26
Links: videoslidesslides + notes

A detailed presentation of why, how and what ResourceLoader does.

Introduction to ResourceLoader
Event: Wikimania 2011 (2011-08-05)
Duration: 00:22:40
Links: videoslidessubmission abstract

Aimed at MediaWiki extension developers, explains the features and how to register and load module bundles.

Migration guidesEdit

Code stewardshipEdit