In Arcaea, an autoplay tool is a program designed to read chart data (typically .aff files) and simulate real-time touch inputs.
: Every year on April 1st, Arcaea releases special "hidden" charts that often feature chaotic or technically "impossible" mechanics. Some of these are designed as "Autoplay" showcases where the game plays itself to demonstrate the visual spectacle of the chart. Nintendo Switch Version
Programs like the now-popular community tools allow users to simulate charts or play custom fan-made charts without risking their official accounts.