Mo. Rev. Stat. § 477.010: Supreme court to promulgate general rules for all courts of the state.

The supreme court shall have the power to direct the form of writs and process; and to promulgate general rules for all courts of the state. No such forms or rules shall abridge, enlarge or modify the substantive rights of any litigant nor be contrary to or inconsistent with the laws in force for the time being.