Cursor modes

Auto Select and Smart Cursor both cut down how much you have to think about while building or mining, and they solve opposite halves of the problem. Auto Select decides what you are holding. Smart Cursor decides where it goes. They work together, and either can be switched off, which is the first thing to try when the game starts doing something you did not ask for.

Hold the Auto Select key, left shift on keyboard by default and a thumbstick press on controller, and the game picks an item based on what the cursor is pointing at. Stone gets a pickaxe, a tree gets an axe, a wall gets a hammer. The item does not have to be on your hotbar, which is the real benefit: tools can live deep in the inventory without costing you a hotbar slot each.

It has opinions about what counts as appropriate. A Flare Gun with no Flares will not be chosen, and candles and other light sources are not treated as usable tools at all. When two items are equally valid it takes whichever appears first in inventory order, so moving your preferred pickaxe higher up changes the result. If the obvious choice is missing it usually settles for the next best thing rather than doing nothing.

Smart Cursor picks a target from the item you are holding rather than the exact tile under the pointer. Left Ctrl toggles it by default, and the cursor becomes visibly wider with a yellow box marking the tile it has chosen. On desktop there is an option that makes the key hold to use instead of a toggle, which removes the whole class of mistake where you forget it is active. The 3DS version runs it by default until you target something with the D-Pad or touch screen.

• Multi tools like the Drax or any hamaxe fall back to axe behavior, so if a tree is anywhere in range that is what they hit, regardless of what you were aiming at.
• Extending platforms is the classic failure. Aim slightly off and the run heads somewhere you did not intend, often several tiles before you notice. Turning the ruler on gives you a reference line to check against.
• Digging near liquids is the expensive one. Smart Cursor has no concept of which block is holding lava up, and it will cheerfully mine the one that was.

In 1.2, Smart Cursor also applied to ordinary blocks, and later versions narrowed what it would touch. That wider behavior can be restored by hand editing the config file the game writes alongside your saves. It is a manual edit rather than an option in any menu, so it is worth backing the file up before you change it.