When consumed, crafting potions temporarily raise the player's Crafting level by 3. This boost may be used to boost crafting levels for quests such as Lost City and Creature of Fenkenstrain. The boost may also be used to reach the level required to craft an item, such as decorated cooking urns at level 78 instead of 81.
This table is based on the Grand Exchange prices of a vial of water, the wergali, and frog spawn. It is accurate assuming all three items are bought from the Grand Exchange and the Crafting potion is sold afterwards (NOTE: the secondary ingredient frog spawn, cannot be bought).