Dota 2 Wiki uses icons and values extracted from Dota 2's game files. This is also a useful way to get attributes of newly released or hard-to-get cosmetic items.
To open Dota 2's .vpk game files, all you will need is GCFScape.
The default installation for Dota 2 will place files at
C:\Program Files (x86)\Steam\SteamApps\common\dota 2\dota (or
C:\Program Files (x86)\Steam\SteamApps\common\dota 2 beta\dota if the game was installed during the beta). Navigate there in GCFScape and open
pak01_dir.vpk. Once you have opened the vpk file, you can see directories and files. Once you have found what you want inside GCFScape, right-click and extract to the desired location on your computer.
To open .vpk files on macOS you'll need to download Gridmount.
The Dota 2 game files are located at
~/Library/Application Support/Steam/steamapps/common/dota 2 beta/game/dota. Double click the file
pak01_dir.vpk and Gridmount will automatically mount the file as a virtual drive.
When you're finished, remember to unmount
pak01_dir.vpk again, by either right clicking it and selecting "Eject" or by simply dragging the icon over the trashcan on the bottom right of the Dock.
Useful locations inside
Cosmetic item data
This is where all the cosmetic item attributes are defined—rarity, slot, hero, associated custom animations or effects, default gems, etc. You can also see contents of sets and treasures.
Cosmetic item icons
Most cosmetic item icons. Loading Screen icons are the same icon as the set icon
Custom cursor item icons.
.vtf files of loading screens in their original resolution. Use VTFEdit to view/convert.
Image files for HUD skins.
Emoticon image strips.
Hero and Announcer Audio
All voice acting for heroes and announcer / mega-kill packs can be found here in their respective sub-directories.
Hero icons, item icons, and ability icons can be found in their respective folders. Custom ability and item icons can be found here too.
C:\Program Files (x86)\Steam\SteamApps\common\dota 2 beta\dota\resource\dota_english.txt
Another one that is not actually inside the .vpk file. Game strings
C:\Program Files (x86)\Steam\SteamApps\common\dota 2\dota\resource
Item names and descriptions can be found here.