Matchmaking

Matchmaking is the process of determining appropriate player pairings when players are queuing up to play Hearthstone.

The matchmaking process functions differently for each game mode. Casual mode, Ranked at Legend rank, and non-cooperative Tavern Brawls determine pairings using each player's matchmaking rating (MMR). Ranked play without a Star Bonus is determined by each player's rank, and Arena pairings are determined by each player's win/loss record for the current run. Casual mode and the Arena feature special mechanics for very new players.

In each case, the goal is the same: to try to find a player of similar matchmaking value (rating, rank or record) as possible. The player's matchmaking value is the only data used in the matchmaking process: other details, such as class, deck, or playing history are not taken into account and never affect matchmaking.

When a player enters the matchmaking queue the system will attempt to find another player in the queue with an identical matchmaking value. If one is found, the two players will be entered into a match with each other. If a perfect match is not found, the matchmaking system will "wait a few seconds" and then search again. However, each time the system fails to find a match, its matchmaking parameters are widened. This ensures players are not left waiting for too long, but as a result, players may occasionally be matched with opponents of significantly different rating, rank, or record.

For information and statistics on specific types of matchmaking, see Ranked, Casual, and Arena.

Matchmaking ratings
Matchmaking rating (MMR) is a special internal rating system used for certain types of matchmaking. Hearthstone uses separate MMRs for different types of play, such as Casual mode, Legend-level Ranked play, and non-cooperative Tavern Brawls. Each MMR is determined independently and does not affect other types of play. MMRs are 'hidden' and cannot be viewed by players.

MMRs are used for the following types of matchmaking:
 * Casual matches (shared between Wild and Standard format )
 * Ranked matches involving at least one player at Legend rank
 * Tavern Brawls (except cooperative Brawls )

MMR is adjusted after each match, depending on the outcome of the match, and the MMR of each player:
 * MMR is gained with wins and lost with losses.
 * The amount of MMR gained or lost is dependent on the MMR of your opponent.
 * MMR adjustments are not affected by the duration of the match; or what cards are in either player's deck.
 * Casual mode MMR is adjusted quickly when a player experiences a win or lose streak.
 * While MMR is not used in sub-Legend Ranked matches without a Star Bonus, it is still recorded and altered after each match. It is unknown whether or not cooperative Tavern Brawls (which do not use MMR for matchmaking) affect the player's MMR.

Ranked mode MMRs are not reset at the start of every season. Casual mode MMRs do not reset. Tavern Brawl MMR does not reset, and carries over from week to week.

New players
In Casual mode and the Arena, new players are initially placed into special matchmaking pools to ease them into the game.

Casual mode
Casual mode matchmaking includes a new player pool. Players are initially placed in a separate pool, allowing them to play exclusively against other new players. After a certain period, players are introduced into the main matchmaking pool. According to Ben Brode, as of April 2016 players remain in the new player pool until they have played 10 games, or have obtained 2 legendary cards. However, this is something that the developers tweak regularly.

Arena
For players on their first few Arena runs, matchmaking is intentionally altered to provide an easier transition into the game mode. For matchmaking purposes, the player's win/loss ratio is considered to have one more loss than it actually does, thus matching them against what should on average be easier opponents. The system will also prefer to match such players against each other.

The exact number of games required to be eligible for this adjustment is something that the developers are "still tweaking a little", but as of April 2016 is "in the realm of 2 or 3 runs." Once the player has exceeded this number of runs, they are matched purely on their win/loss ratio, with their number of previous runs no longer affecting their matchmaking.

Variation with time of day
All forms of matchmaking function to find a suitable opponent from the currently available pool of players. Pairings are therefore affected not only by each player's rating or rank, but by which other players are currently awaiting matchmaking. For example, different times of day often attract different types of players, with certain times typically featuring a slightly more competitive pool of players. Because of this, each type of ranking is entirely accurate only for that same quality of population. Such variations are not fixed, and may vary by day, time of day, or in relation to calendar or game-related trends.

Because wins and losses will ultimately result in an adjusted rating or rank, such variance can also lead to a yo-yo effect with pairings. For example, a player who normally plays Casual in the mornings may try playing at another time of day, only to find the competition more fierce. This discrepancy in the player's matchmaking will likely lead to the player losing several games in a row, resulting in the player's MMR dropping rapidly in order to select opponents of equal ability. However, should that player then return to playing in the mornings, they may find the opponents selected for them to be extremely easy to defeat, due to the adjustment of their MMR.

Player bias
A common complaint from players is that the matchmaking system is intentionally matching them against opponents using decks designed to beat them. For example, a player may play several matches using a control deck, during which time they lose repeatedly to a particular midrange deck currently common in the meta. In response, they may switch to an aggro deck designed to defeat the midrange deck, only to find themselves facing an opponent using their previous control deck, resulting in yet another loss. Some players report a strikingly consistent pattern of being matched against decks with a strong chance of defeating them, resulting in a long run of losses, and an equally large amount of frustration.

Blizzard have consistently denied that the matchmaking system has any such knowledge of player decks, match-ups or history. The perception is more likely due to the tendency of players to notice and remember runs of bad luck more than runs of good luck, and losses more than wins. Players who are matched into several advantageous match-ups in a row are more likely to celebrate their luck, commend their choice of deck or knowledge of the meta, or simply focus on playing, than to make a mental note of the mathematical improbability of such pairings being purely random. Conversely, players presented with a string of bad match-ups tend to seek a reason for their luck - ideally someone or something to blame - and are far more likely to make a post complaining about their misfortune.

While it may seem at times that the Hearthstone matchmaking system has achieved sentience and is hell-bent on preventing you from reaching Legend, it is therefore likely that such experiences are simply a result of the tendency of the human mind to remember and focus on negative experiences, combined with the at times extraordinary runs of luck that inevitably occur every so often in any such game of chance. If you're getting frustrated by a string of losses, remember that frustration typically results in impaired performance, and take a break.

As you reach the rank of your skill level, the average win rate for a deck you're playing will start approaching 50%. The game does not force this winrate upon you, it's a consequence of balancing a good deck with bad plays, or a bad deck with good plays.

Patch changes
NB: The following list is incomplete.
 * Unknown Patch (2019-06-03): Reduced chances of matching against the same player multiple times in a row. Players in ranks 25 – 21 should now face opponents of more similar skill level.
 * Improved matchmaking for new players.