Abstract: A method and system is disclosed for providing a programming interface (PI) specification which defines in text form the format of data messages for communication between, for example, financial services counterparties for making transactions. The system includes one or more physical processor in communication with physical data storage, the one or more processors being configured to: provide in data form a base PI specification for display on a computer; send said base PI specification, or a copy thereof, to a computer for display and editing through a user-interface; receive from said computer at least one edit made to said base PI specification through the user-interface; provide a sub-specification of said base PI specification incorporating the at least one edit made in (iii); and make the sub-specification available for viewing at remote computers over a data network.