High Level Alchemy (high alch, hi alch or alching) is a non-combat spell used to convert items into coins at the best price player could get from a specialty store. The amount of coins generated is normally 60% of the speciality shop price or 150% Low Level Alchemy prices.
High Level Alchemy is a popular way for mid and high level players to train their magic level, by buying or making valuable items and nature runes, then casting the spell on the items.
High (and Low) Alchemy can be cast on noted items, saving much withdrawal time from the bank, and simplifying the "click pattern".
Casting alchemy spells on stackable items will only alchemize one at a time
High level alchemy is often used while Slaying to high alch the rune drops and sometimes the dragon drops. This gives you good mage xp aswell as good money as rune items are a common drop on high leveled monsters such as Smoke Devils and Abbysal Demons.
Attention: High alching does damage to you every now and then in order to stop people from autoclicking it. It's adviced to keep your health up so you don't accidently kill yourself while high alching which may result in items lost. You're allowed to use autoclickers but you're not allowed to afk-train. So always watch your screen or every minute or so.