Oracle Text

Cleric spells you cast cost WB less to cast. This effect reduces only the amount of colored mana you pay. (For example, if you cast a Cleric spell with mana cost 1W, it costs 1 to cast.)

Card Rulings

10/4/2004 If you have more than one of these on the battlefield, the cost reduction is cumulative.
8/1/2008 You apply cost reduction effects after other cost modifiers, so it can reduce additional costs or alternative costs if they include and/or .
8/1/2008 If a spell has hybrid mana symbols in its mana cost, you choose which half you will be paying before determining the total cost. If you choose to pay such a cost with or , Edgewalker can reduce that part of the cost.