The law staff is a magic weapon that costs 10,000 Dungeoneering tokens and requires level 45 Dungeoneering and 45 Magic to acquire and wield. Players can store up to 1000 law runes in it and remove them at anytime. When wielded, there is a 1/10 (10%) chance that all law runes are saved when casting a spell that requires such runes. This effect also works with Magic tablet creation. Law staves do not stack in the bank, even if they have the same rune count.
Although it may seem as though the law staff's ability would save the player more money due to law runes being more expensive, the fact that there is only a 10% chance of saving a rune means that the monetary savings after casting 10 spells only amount to 398 coins (the price of one law rune), or 39.8 coins per spell on average. With a staff of air or similar staff which provides unlimited air runes, the savings for the same 10 teleports amount to 1200 after preserving 30 air runes, proving much less costly in the long run.
Most free players prefer using the nature staff to law staff in combat due to the higher tier (53 for nature, compared to 45 for law).
The following is a comparison of the cost per cast of spells using law runes while using an elemental staff as opposed to using a law staff. The cost per cast when using the Law staff is approximate and assumes that exactly 1 out of 10 Law runes are saved.
Example on reading the table:
The cost of Varrock teleport using a fire staff is 518 gold.
The cost of Varrock teleport using a law staff is 580.2 gold.