Rarity is a rough measure of the quality and scarcity of a card. Cards of higher rarity are typically more powerful or more useful, but are much harder to find and more expensive to craft. Conversely, rarer cards can also be disenchanted into larger amounts of raw materials.
There are 5 rarities: Free, Common, Rare, Epic and Legendary. Each quality has its own color, based on World of Warcraft's gear system, and rarities can generally be recognised by the color of the gem at the bottom center of the card's portrait (see display, right). The exception is cards from the basic set, which do not feature colored gems. When opening packs, face down cards above common quality will be displayed with an appropriately-colored glow when hovered over.
For cards in the expert set, rarity determines how likely a card is to be found in a card pack, with higher rarities occurring less often. However, with the exception of basic cards, rarity does not determine the means by which cards are obtained, with all cards from a given set usually obtained by the same means, regardless of rarity. For details, see Card set and individual card pages.
Rarity in Hearthstone cards serves as a rough indication of quality, but an inconsistent indication of value in play. Likewise, for cards in the expert set, rarity is a consistent indicator of card scarcity and crafting cost. However, for cards in other sets, rarity may bear no relation to the difficulty of acquiring cards.
Legendary cards boast some of the most powerful effects in the game, and adding a single well-chosen legendary to a deck otherwise lacking in high rarity cards can measurably improve the deck and win games. Some high rarity cards may also represent improved versions of lower rarity cards, providing fairly straightforward upgrades for decks using these cards. In most beginner decks, adding almost any legendary is likely to improve the deck, and in many lower-rank games, drawing and playing a lone legendary minion can single-handedly turn the tide of battle and win the game. Low-level battles are sometimes decided by who is able to draw their Ragnaros the Firelord or Ysera first.
However, despite the undeniable power of many legendaries, rarity is not the prime determinant of victory in matches. Overall deck composition (as well as skill, luck and match-ups) is a far larger factor, and despite the power of many legendaries, most top-level players choose to include only a handful legendaries in their decks. Streamers such as Trump have demonstrated the ultimate unimportance of rarity by reaching Legend rank using mostly basic cards, while some such as TotalBiscuit have even constructed decks composed entirely of legendary cards, in order to demonstrate how ineffective and cumbersome such decks would be.
Ultimately, while higher rarity cards offering straight upgrades to lower rarity cards can generally be relied upon to present a superior option, the optimal deck for any given deck type is likely composed primarily of low and medium rarity cards, including many basic class cards. Many lower rarity cards provide essential functions and utility not found in higher rarity options, as well as low mana cost cards invaluable for early and mid game presence. As a result, a free Polymorph may very effectively counter a legendary Cairne Bloodhoof, and a basic Sacrificial Pact may turn the legendary Lord Jaraxxus into a swift defeat.
Deck composition is ultimately determined by several factors, including both individual card quality and overall deck strategy. The ability of a card to serve a deck's specific needs and approach to obtaining victory will always play a greater role in determining its viability than its rarity. However, a few well-chosen high rarity cards can turn a deck from bad to reasonable, or from good to great, and can generally be relied upon to provide some exciting and game-changing options.
Free is the lowest level of card rarity, below common, rare, epic and legendary. All free cards belong to the basic set, and therefore do not have any colored gems at the bottom-center of the card's art.
Two of each free card are automatically included in the player's collection.
There are 59 free cards (5 per class and 14 neutral).
For a full list of all free cards, see Free card list.
Common is the second-lowest level of rarity, above free, but below rare, epic and legendary. Common cards that are not from the basic set can be recognised by a white gem located at the bottom-center of the card's art, and when opening packs do not glow when moused over. Basic common cards do not feature the white gem, but are still marked as common cards. There are more common cards than of any other rarity, and common cards are obtained from card packs more frequently than any other rarity.
Basic common cards that are non-class-specific are automatically included in the player's collection, while all class-specific basic common cards can be obtained by levelling a hero of the appropriate class to level 10. Common cards from other sets can be obtained through the means usual to those sets.
For a full list of all common cards, see Common card list.
Rare is the level of rarity above free and common, but below epic and legendary. Rare cards can be recognised by a blue gem located at the bottom-center of the card's art, and when opening packs will display a blue glow when moused over.
For a list of all rare cards, see Rare card list.
Epic is the second-highest level of rarity, above free, common and rare, but below legendary. Epic cards can be recognised by a purple gem located at the bottom-center of the card's art, and when opening packs will display a purple glow when hovered over.
For a full list of all epic cards, see Epic card list.
Legendary is the highest level of rarity, above free, common, rare and epic. Legendary cards are indicated by an orange gem located at the bottom-center of the card's art, and when opening packs will display an orange glow when moused over. In addition, legendary cards also feature a dragon around the portrait, much like elites and rares in World of Warcraft. Legendary cards are obtained from card packs less frequently than any other rarity.
Unlike cards of other rarities, you may only have one of each legendary card in your deck. Playing a legendary card prompts a short piece of unique music. In addition to being very powerful cards, the characters featured in legendary cards are typically very well-known or significant within Warcraft lore. Legendary minion cards obtained through adventures tend to depict bosses from that adventure.
While most legendaries are extremely rare and hard to obtain, legendaries in the Naxxramas set can be obtained relatively easily once the Curse of Naxxramas adventure has been unlocked. However, the cost of purchasing the adventure itself can be considered some compensation for this.
For a full list of all legendary cards, see Legendary card list.
 In development
- The developers have stated that legendary spells and weapons may be a possibility in the future.
- JR Cook (2014-04-13). Interview with Eric Dodds and Jason Chayes, PAX East 2014.