Agar.io is a massively multiplayer action game created by Matheus Valadares. Players control a cell in a map representing a petri dish; the goal is to gain as much mass as possible by swallowing smaller cells without being swallowed by bigger ones. The name Agar.io 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 downloadable Steam version was announced on 3 May 2015, and the mobile version of Agar.io for iOS and Android was released on 8 July 2015 by Miniclip.