Wis. Stat. § 240.10: Real estate agency contracts.

(1) Every contract to pay a commission to a real estate agent or broker or to any other person for selling or buying real estate shall be void unless such contract or note or memorandum thereof describes that real estate; expresses the price for which the same may be sold or purchased, the commission to be paid and the period during which the agent or broker shall procure a buyer or seller; is in writing; and is subscribed by the person agreeing to pay such commission, except that a contract to pay a commission to a person for locating a type of property need not describe the property.

(2) Every contract to pay a commission to any real estate agent or broker or to any person for leasing real estate for a term exceeding 3 years shall be void unless such contract, note or memorandum thereof describes that real estate; expresses the rent to be paid or a method to determine the same, the length of the lease, the commission to be paid, and the period during which said person shall procure a tenant; is in writing; and is subscribed by the person agreeing to pay such commission, except that a contract to pay a commission to a person for locating a type of property need not describe the property.