What you can see from outside

Most of what a hive tells you, it tells you before you ever lift the lid. Entrance traffic is the first signal: a steady stream of bees leaving and returning loaded with pollen means a queen is laying and forage is coming in; a quiet entrance in good weather is worth investigating.

Bearding, a mat of bees clustered on the front of the box in hot weather, usually just means the colony is crowded and cooling itself, not that anything is wrong.

The most useful outside check costs nothing: heft the back of the hive off its stand. A colony that feels heavy is carrying stores; one that feels light, especially in spring after a long winter, is running on empty at the worst possible time to run out.