The oii browser extension is designed specifically for osu! players, adding an improvement indicator (ii) to user profiles on the osu! website. This metric allows users to gauge their improvement speed compared to the average player, with values indicating whether they are improving faster, slower, or at the average rate. The extension seamlessly integrates with osu! profiles, displaying the ii value alongside the player's playtime, and offers an option to manually adjust playtime based on other clients or offline play.

In addition to tracking improvement speed, oii includes a feature to estimate when a player might reach a certain performance points (pp) threshold, based on their individual improvement curve. While this feature serves as a fun and engaging gimmick, it's important to note that the extension is still in early release, which means users may encounter bugs and changes in functionality as it evolves. Overall, oii provides useful insights for osu! enthusiasts looking to track and enhance their gameplay.