Queuing and Matchmaking (2024)

Matchmaking is the algorithm that calculates the best possible matching of players into teams and against each other among the set of all players presently waiting in the queue for a game. The preferred result is a game where every team has an equal probability of winning. In online games that offer competitive experiences, matchmaking is usually facilitated by a rating number that determines the absolute skill of each player. This skill rating is computed through various algorithms itself.^[1][2]

In League of Legends, matchmaking prioritizes the highest uniformity of skill ratings between players and teams, the best queue times, as well as proper role selection for queues that require it.^[3] The rest of this article pertains to matchmaking in League of Legends specifically.

Queuing[]

A matchmade queue, or simply queue, is the list of all players currently waiting for teams to be created by the matchmaker. These players may be playing alone or in a pre-made party, or simply party, with other players. Entering a queue (= queuing) takes place in the lobby after clicking on the Find Match button at the bottom. At that point, matchmaking begins.

Queue types differentiate the preferred matchmaking conditions.

• A co-op queue is a casual queue type that can match players over a very wide band of skill ratings against Artificial Intelligence robots (= "bots") and has no restrictions on parties of players.
• A normal or unranked queue is a casual queue type that matches players within a potentially wide band of skill ratings and usually has loose restrictions on parties of players.
• A ranked queue is a competitive queue type that is involved in the League system and typically matches within a narrow band of skill ratings.
• A codependent queue, such as the one used in Clash with "Tiers", generates a ranking for each player that is determined by their skill rating in other queues, rather than the codependent queue itself.

Queues may impose additional restrictions on players, subject to each queue's needs. For example, Co-op vs. AI and Ranked game queues have different summoner level and owned champion requirements; rank differences between party members when queuing in Ranked Solo/Duo cannot be too large; different party members cannot choose the same primary role in Draft Pick; parties of four cannot queue together in Ranked Flex; and many other examples. Imposed queue restrictions will inform all players in the lobby through a message bubble, and disable access to queuing if the queue's requirement(s) are not being met.

During queuing, matchmaking estimates an average expected duration for the particular queuing player to be matched into a game.

Ready check[]

When enough players have been found to create a full game, a 'Ready' check screen with the options Accept and Decline will pop up for 12 seconds. The player must interact with it to confirm if they are AFK or not.

If the player accepts but at least one other matched player does not, queuing continues after the screen elapses. If the player declines or there is no response from them, the check is assumed declined and queuing stops for the declined player's party.

The client automatically restores upon the 'Ready' check ensuing.

Skill determination algorithm[]

The skill rating in League of Legends is termed Hidden Matchmaking Rating, hMMR, or simply MMR. As the name implies, this rating is indefinitely hidden, and its exact parameters are proprietary to Riot Games. In ranked modes specifically, MMR is visually replaced by the superficial "League" system—visual ranks can only serve as an approximation for a player to assess their own skill, but create an important layer for multiple other calculations to be made for players without affecting the integrity of MMR (e.g. League Points compensation for losing a game with a disconnected player on the ally team).^[4][5]

A player's MMR estimates how good a player is solely based on whom the player wins and loses against. Every player that joins a matchmade queue for the first time begins at a set "starting MMR". However, entering a ranked queue can be influenced by the map's equivalent normal queue, if the latter exists and at least one game has been played in it. Ranked queues are strictly not influenced by each other.^[6]

Individual MMR is averaged into each team's MMR, and weighted based on the disparity between the best and worst player in the game or whether a given player is playing on a team's skill level compared to their MMR. Wins and losses which happen as a team then influence individual MMR gains and losses, and over a larger number of games the system will eventually be able to more accurately determine the skill rating of a player due to their win and loss record. If that player continues to win these assumed balanced games, they will continue gaining MMR until they either are at their skill level and no longer gain more MMR than they lose, or are among the top players in the server.

Adjustments from the baseline MMR gains and losses can occur in the algorithm in order to account for a player who is winning more or losing more than is expected. The degree of adjustments is influenced by various indicators of a player's habits and performance at their assumed skill level, and the intended goal is to expedite the algorithm placing the player in their actual skill rating. Most importantly, indicators such as scorelines (KDA, Creep score, etc) are not considered in any way, since the system would be open to exploiting.^[5]

Matchmaking algorithm[]

Matchmaking attempts to create fair matches after considering the set of rules for the given queue. In the ideal case, the matchmaker wants to find a full game of players who are at identical MMR and have queued at the same time. In this case, it will not be able to guess the outcome of the game with any certainty, meaning both teams have a truly equal probability of winning.

The ideal case is very rare, and the most important rule to consider during matchmaking is a time constraint since a game must evidently happen at some point. When the matchmaker fails to find available players within its strictest limitations, it will fail, loosen the restrictions a little, and start searching anew while also trying to find new queuing players who would pass the restrictions desired at a previous and the current step. If the matchmaker fails again and again to match enough players for a game, this will inevitably result in larger and larger skill deviations between the best and worst player in the game.

Parties of players with very different MMRs, different sizes of parties, returning players after long absence, times of day where there is low activity, and unpopular roles, are only some of the disruptions to the ideal matchmaking that the matchmaker has to resolve in order to determine what available matching of players is the next best and most preferable.^[3]

Autofill[]

In certain queues that include role selection, players may be automatically assigned to an unpopularly selected role for their queue as a last resort in order to speed up matchmaking. This system is called Autofill. The "Fill" role selection functions in the same way.

Roles that are low in supply for a queue at the time relative to others will have Priority, which is indicated in the role selection menu. Priority roles dynamically update very regularly and may vary per region and time of day.

Some queues explicitly require the player to select at least one Priority role, whereas others do not enforce this. For queues that do not enforce the selection of a Priority role, when the player does not select a Priority role the lobby will inform them that Autofill is activated. If matchmaking fails to find an available player in a reasonable amount of time, they may then be automatically assigned to a Priority role (= Autofilled) . Selecting a Priority role ensures Autofill Protection, meaning the player receives at least one of the roles that they have selected for the upcoming game, and are not Autofilled.

Upon the player completing a game (including remade games) after they were assigned Fill or were Autofilled, they also receive Autofill Protection for the next game in that same queue, regardless of Priority roles.

Team Parity[]

In addition to skill rating calculations, team parity systems are employed during matchmaking that can potentially minimize imbalances and compensate for differences in skill rating among teams and players in role experience, preference, as well as Autofill and parties.^[7][8] The system internally evaluates the overall role preferences of players in a given queue, and tries to pair them within a certain time. If no parity-accurate match can be found within a reasonable amount of time, team parity fails and matchmaking proceeds without it.

The priority of parity conditions is as follows [top-to-bottom]:

1. Party size parity

• Matchmaking attempts to pair the size of parties. For full parties, this condition takes precedence over all others and is much stricter (within a reasonable time constraint).

2. Primary and Secondary role parity

• Matchmaking attempts to pair Primary preferences with Primary preferences, and Secondary with Secondary.

3. Autofill role and number parity

• Matchmaking attempts to pair the number of Autofilled players on one team with the number of Autofilled players on the other team, as well as the role of those Autofilled players.

4. Revival parity

• Matchmaking attempts to pair returning players against other returning players.

It is a fact that team parity systems will almost always fail at the extremes—very high or very low—of the skill rating distribution, since the number of players within those skill ratings is significantly lower. The current restriction of queuing in a party of two ("duo queue") in Ranked Solo/Duo at Apex tiers is one case of such a fault of matchmaking being foreseen.^[9]

History[]

See Elo rating system#Goals for Matchmaking and Rank (League of Legends)#Development for further reading.

References[]