In the field of specialized hardware for digital gaming, an increasing number of products not only promise ever-increasing precision, but also provide self-tracking functions intended to quantify the player’s gaming activities and actions. We position these developments at the intersection between the Quantified Self movement and the tradition of playful selfmeasurement. Building on practice theory, we raise the following questions concerning the datafication of gaming practices and the use of what we call playful metadata: What do players and game developers do with data that is generated within, and in relation to, games? How does the emergence of playful metadata modify interactions, both between players and between the players and the game? By analyzing exemplary quantifying practices found in the contexts of speedrunning, competitive gaming and game streaming, we identify three central motives for quantified gaming: 1) the appropriation of games’ spaces and goals by players who define their own parameters of success by quantifying their gameplay; 2) the production and communication of individual performance careers aimed at modulating the player’s affects towards their own performance; 3) the production of data for competitive comparability and/or cooperative sharing of knowledge.