RoleIcons is a tiny UI mod that adds Blizzard's party/raid role icons (tank/heal/dps) in several useful places in your UI, and provides several other related features.

Role icons are added to:

The Blizzard raid tab. The role icons replace the level field for max level players.
Game tooltip when you mouse over a player or raid frame
Target frame
HealBot unit frames
HealBot and Vuhdo tooltip when you mouse over a raid frame
Party/Raid chat (Blizzard chat frames, Prat, Chatter, WIM)
NEW in 4.2: System messages that mention group members
NEW in 4.3: Player popup context menus
NEW in 4.4: Group member tooltips on map and minimap

Other features:

Enhances the Blizzard Raid tab with role summary counts and class summary counts
Adds a role-check button to the Raid tab
Blizzard Raid tab can now be left-clicked to target a raid member
Blizzard Raid tab can now be middle-clicked to set a raid member's role
Automatically sets your role based on your spec when joining a raid or respeccing
Automatically replies to role checks from the raid leader based on your spec
Adds a tooltip showing the tier token breakdown for the current raid members
NEW in 4.0: Displays the "hosting" realm name while in cross-realm groups, showing when it changes and why
All features are optional and can be toggled using /ri

Basic Usage:

Install as usual
It Just Works! (tm)

Command Line Usage:

/ri help - Get info on command-line options
/ri check, /rolecheck - perform a Role Check (must be leader or raid assistant)

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Bug reports or feature requests
Forum thread for general discussion