AddOns (sometimes called add-ons, or mods) are collections of Lua/XML code that augment, modify, or replace World of Warcraft's default user interface. Addons vary greatly in scope and size — they may display information not presented at all by the default UI, add functionality to the default UI (e.g. additional buttons you can press to do things), modify the default UI's appearance (e.g. by changing colors or positions of UI elements) without changing its functionality, or even replace the default UI entirely.
Some addons are standalone, and are able to run without any additional addons being installed; others can require certain other addons to be installed to work at all, or integrate with other addons to provide additional functionality. Collections of addons that have been put together to form a coherent user interface are sometimes referred to as UIs.
With the release of Patch 3.1, Blizzard Entertainment introduced an official UI Add-On Development Policy that limits how addon authors can distribute their addons. In particular, addons must be available free of charge, and may not include advertisements or solicit donations in-game.
Types of addons
There are several broad categories of functionality provided by addons:
- Unit Frame addons
- Customize how your, your party's, or your raid group's health/mana/debuffs/buffs are displayed, and allow you to target specific players.
- Action bars
- Provide additional ways to trigger your class abilities.
- Boss mods
- Provide timers and warnings for boss encounters.
- Information displays
- Allow at-a-glance access to information like durability, current wealth, location of current quest objective, combat stats, etc.
- Visual customization
- Modify how the user interface looks, for instance by adding backgrounds or customizing the appearance of common UI elements.
Of course, there are also many addons that do not fit within any of these categories. You can explore the various available addons by browsing addon sites.
Installing an addon
In general, you can install an addon by extracting its code into the "World of Warcraft\Interface\AddOns" directory. More specifically, you should:
- Download and extract the addon you want to install. Addons are typically distributed in .zip archives; save the .zip file somewhere and extract it its contents:
- On Windows (XP or later), you can double-click the .zip archive to view its contents in Windows Explorer.
- On Mac OS X, you can double-click the .zip archive to extract its contents into the current folder.
- Locate your "World of Warcraft" folder. It should contain the "Wow.exe" or "World of Warcraft.app" applications.
- On Windows, it usually is "C:\Users\Public\Games\World of Warcraft" or "C:\Program Files\World of Warcraft\"
- On Mac OS X, it usually is "/Applications/World of Warcraft/"
- Go into the "Interface" subfolder of your "World of Warcraft" folder. If it does not exist, create it.
- Go into the "AddOns" subfolder of your "Interface" folder. If it does not exist, create it.
- Move the addon directories extracted from the .zip archive into this "AddOns" folder.
- You've done this step correctly if there's now an "World of Warcraft\Interface\AddOns\KittenMod\KittenMod.toc" file, where KittenMod is the name of the directory used by the mod you've decided to install.
- Restart World of Warcraft, then log into the game. On the character selection screen:
- The "AddOns" button should appear in the lower left corner of the WoW window.
- If you've installed the addon correctly, it should appear in the list of addons that shows when you press the "AddOns" button.
- You may need to check the "Load out of date AddOns" checkbox on the "AddOns List" frame in order to permit the addon to load.
Loading out-of-date addons
AddOns that have not been updated since the last minor version (i.e. x.y.0) patch of World of Warcraft will be displayed as "out of date" by the World of Warcraft client, and will not be loaded by default. However, because most addons do not actually need to be updated for every minor patch, such addons may still function correctly.
To enable loading of addons that appear "out of date," check the "Load out of date AddOns" checkbox in the "AddOn List" frame accessible by clicking the "AddOns" button on the character selection screen. Blizzard automatically clears this checkbox with every client patch, so you may have to re-check it periodically.
Troubleshooting an AddOn
As of Patch 2.3, if you get a message "Interface action failed because of an AddOn", this means that an AddOn interfered with the Blizzard UI in some way. To diagnose this, enter the following into chat "/console taintLog 1" and restart the game and try to reproduce it. If you reproduce it, you can quit the game and search through the file Logs\taint.log for the word "blocked" and mail the log to the author of the AddOn listed there. Once you have done this you can turn off logging by entering the following into chat "/console taintLog 0"