The development of Hearthstone at Blizzard was inspired by two directions, according to developer Eric Dodds: a desire for Blizzard to develop something more experimental with a smaller team in contrast to their larger projects, and the shared love of collectible card games throughout the company. Blizzard executives, around 2008, had considered that their revenue was primarily sustained on three well-established properties (the Warcraft, StarCraft, and Diablo series), but saw the rise of small independent developers with highly successful projects, representing a shift in the traditional video game model. To explore this new direction, Blizzard brought a number of people into "Team 5", named after being the fifth development team formed at Blizzard. Initially, the team had between 12 and 15 members, in contrast to other Blizzard games with teams in excess of 60 members. By November 2015, the team had 47 members.
Of the game types they explored, Team 5 soon focused on the collectible card game approach, given that many on the team and in Blizzard had played such games since their introduction. The team found it natural to build the card game around the existing Warcraft lore; according to production director Jason Chayes, Warcraft was already a well-known property, and the depth of characters and locations created for other games in that series made it easy to create cards inspired by those. They also saw that new players to Warcraft may be drawn into the other games through playing Hearthstone.
The team was able to pull concepts and art from the pre-existing World of Warcraft Trading Card Game, first published in 2006 by Upper Deck and later by Cryptozoic Entertainment; when Hearthstone was near completion, in 2013, Blizzard terminated its license with Cryptozoic as to favor their pending digital card game. The addition of heroes, an aspect from the previous trading card game, was found to help personalize the game for the player to allow players to discover useful combinations of cards for each hero.
After about a year of starting development, the team had produced an Adobe Flash prototype of the game that offered the core card game mechanics and the unique heroes. At this point, several on Team 5 were temporarily moved into other teams to complete the release of StarCraft II: Wings of Liberty. This 10-to-11 month period was considered fortuitous by the team, according to Chayes. Principal designers Dodds and Ben Brode remained developing Hearthstone, and the two were able to quickly iterate many ideas using both the prototype and physical replicas to fine-tune the game mechanics. Secondly, those that were put on StarCraft II came back with ideas based on StarCraft's asymmetric gameplay to help balance the various heroes while still creating a unique characterization and play-style for each.
Further development on the game's user interface began using the principle that the game needed to be both accessible and charming, being able to draw in new players and to be clear how to play the game. Unity is used as the game engine in the interest of speed and to make the game run smoother since the server is where all of the rules exist and calculations happen then the server tells the client what happened[citation needed]. Dodds stated that "it's important that you don't have to spend a lot of time understanding the rules to play the game, the depth grows as you go." Gameplay elements such as pre-made decks for each hero, deck building helps, and visual cues on which cards could be played were used to guide new players. Card text was written in a way so that a new player should be able to immediately understand the effects.
From the beginning, the game was designed to be played solely online and to mimic the feel of physical cards to make it more accessible to new players. Dodds found that past attempts to digitize physical card games by other companies left areas they felt were lacking, and wanted to improve on that experience. One particular example is card games where players have the ability to react to other players; Dodds noted that when playing in the same room as another player, these types of interactions are straightforward, but consume a great deal of time in a virtual space. Hearthstone was designed to eliminate any gameplay from the opponent during the player's turn, streamlining the game.
Other aspects of the game's interface were set to replicate the feel of a physical game being watched by an audience: Hearthstone starts with the player opening a box, during gameplay the cards waver and move while in their hand, and cards when played slam down on the board. When attacking, cards leap across the board to strike the target; when a massive spike of damage is dealt, the board shakes; when a massive creature is summoned, the unseen audience gasps in awe. Hearthstone also offers interactive boards. The boards on which the cards are played can be interacted with in various ways, such as virtually petting a dragon, although the feature is purely for entertainment and has no effect on gameplay.This idea came out from the movie Jumanji in which a board game comes to life, and also mimics how physical card players would often toy with their cards while waiting on their opponent.