How to know if attack speed works on Legendary items listed in AH?

Any item that has the affix "Increases attack speed" increases the attack speed of the item it's on, meaning if it's on a weapon, only that weapon will be increased even if you dual wield. This also means that any pieces of armour with "Increases attack speed" won't have any effect, as they can't attack.

Any item with the prefix "Attack speed increased" increases the attack speed of all equipped weapons, therefore, if it's on a piece of armour it will still work.

So:

• IAS - Increases attack speed = BAD (except on weapons)
• ASI - Attack speed increased = GOOD

Many different sources.