What are Redux Toolkit slices?

A slice in Redux Toolkit is a collection of Redux reducer logic and actions for a single feature. Created with createSlice(): const counterSlice = createSlice({ name: "counter", initialState: { value: 0 }, reducers: { increment(state) { state.value += 1; }, decrement(state) { state.value -= 1; }, setAmount(state, action) { state.value = action.payload; } } });. RTK auto-generates: action creators (counterSlice.actions.increment()), action types ("counter/increment"), and the reducer function (counterSlice.reducer). The "mutating" syntax inside reducers (state.value += 1) is safe because RTK uses Immer — it detects mutations and produces a new immutable state. Use Immer-safe mutations: state.items.push(item), state.items.splice(index, 1). Add to store: configureStore({ reducer: { counter: counterSlice.reducer } }). Slices organize Redux code by feature domain rather than by type (actions folder, reducers folder).