THE HELIOPHYSICS APPLICATION PROGRAMMING INTERFACE (HAPI) IS A RECENTLY DEVELOPED STANDARD FOR SERVING TIME SERIES DATA OVER HTTP USING A REST API. THE DEFAULT OUTPUT FORMAT IS JSON FOR METADATA AND CSV FOR DATA; A SERVER MAY SUPPORT OPTIONAL JSON AND BINARY DATA FORMATS. THE PRIMARY DESIGN CONSIDERATIONS WERE (1) THE METADATA PROVIDED SHOULD BE AT A MINIMUM OF THAT WHICH IS REQUIRED FOR A PROGRAM READING THE DATA TO PRODUCE A PLOT WITH UNITS AND BASIC LABELS (2) DATA ARE DELIVERED AS A SINGLE STREAM OVER THE REQUESTED TIME RANGE (NO INDIVIDUAL FILES OR REDIRECTS TO A URL WHERE A RESPONSE FILE WILL BE FOUND) AND (3) A BASIC HAPI SERVER SHOULD BE STRAIGHTFORWARD TO IMPLEMENT.