Removing a cassette is a fundamental workshop task, whether you're cleaning the drivetrain, swapping sprocket ratios, or replacing a worn cassette at the end of the season. But it requires the right tools. A cassette lockring tool and chain whip work in combination: the chain whip holds the cassette body against the rotational force while the lockring tool engages the splines and breaks the lockring free.
Cassette removal requires two tools working together:
Cassette lockring tool - Engages the splined interface on the cassette lockring, the threaded ring that holds the sprocket stack onto the freehub body. Most road and gravel cassettes use a Shimano-compatible spline pattern (also used by SRAM and most third-party cassettes). Campagnolo uses a different interface and requires a Campagnolo-specific tool.
Chain whip - A length of chain attached to a handle, used to hold the cassette body stationary while you apply torque to the lockring tool. Without a chain whip, the cassette spins freely and the lockring won't loosen. These two tools are often sold individually or as a paired set, if you're buying for the first time, a matched set from Park Tool is the most reliable starting point.