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By default, Compose identifies each row by its position in the list. Item zero is item zero, item one is item one, and so on.

When you insert or remove a row, every item below shifts position. Compose now thinks those rows are different and rebuilds them needlessly.

Rebuilt rows lose their state and animations. A removed item can make the whole list flicker as Compose reshuffles everything below it.

A key is a stable, unique value that names each item by identity, not position. Then Compose follows items even as they move.

The best key is a true unique id from your data, like a database id. It stays the same no matter where the item sits.

Every key in the list must be different. Duplicate keys throw a runtime error, so never key items by a value two rows might share.

Using the index as a key defeats the purpose, since indexes shift just like position. Reach for it only when you truly have no id.

With stable keys, a row's remembered state travels with it. A checkbox stays checked even after items above it are deleted.

Stable keys let Compose animate items moving, appearing, or leaving. Without them, it can't tell a move from a rebuild.

The itemsIndexed builder also accepts a key lambda. You still get the index, plus stable identity for every row.

For any list that can change, adding keys is a tiny effort with a big payoff: correct state, smooth animations, and fewer rebuilds.

What makes a good list key?

Keys give items identity beyond position. Use a real unique id, keep keys unique, and your state and animations just work. ✨