Stick drift
Also called joystick drift · analogue drift · Joy-Con drift
Stick drift is when an analog stick reports movement while nobody is touching it. Games read it as input, so your character or camera moves on its own.
The controller test reads each axis at rest on the browser scale of -1 to 1. Readings up to 0.05 are normal tolerance and anything above 0.10 usually beats the deadzone in games.
In practice
Drift is the most common controller failure. It starts small and usually gets worse. At first a game’s deadzone hides it and you only notice it in menus or when aiming precisely. Later the character walks on its own. Most standard controllers use potentiometer sticks that wear with use, so drift is a matter of time.
How to check
Put the controller flat on a desk without touching the sticks and run the drift measurement in the controller test. Readings up to 0.05 are normal. Past 0.10 most games can’t hide it. Cleaning around the stick base sometimes helps for a while. Lasting fixes are a warranty claim, a stick replacement or a Hall effect upgrade.