Agar.io is a massively multiplayer online action game created by Matheus Valadares. Players control one or more cells in a map representing a petri dish. The goal is to gain as much mass as possible by eating agar and cells smaller than the player’s cell while avoiding larger ones which can eat the player’s cells. Each player starts with one cell, but players can split a cell into two once it reaches a sufficient mass, allowing them to control multiple cells. The name comes from the substance agar, used to culture bacteria.
The game was released to positive critical reception; critics particularly praised its simplicity, competition, and mechanics, while criticism targeted its repetitive gameplay. Largely due to word of mouth on social networks, it was a quick success, becoming one of the most popular web and mobile games in its first year. A Steam version was announced on 3 May 2015 (though never released as of 2018), and the mobile version of Agar.io for iOS and Android was released on 24 July 2015 by Miniclip. Agar.io has inspired similar web games called “.io games”, including games with a similar objective but different characters, and games that incorporate elements of other genres like shooter games.