The Heliophysics Application Programmer's Interface (HAPI) data access specification is a RESTful API and streaming format specification for delivering digital time series data.
The HAPI specification describes a minimum set of capabilities required for a server to provide access to time series data values within one or more data collections.
Current stable release: Version 3.3.1 (PDF) (HTML)
Current draft version
For a list of clients, servers, verifiers, and other tools, see http://hapi-server.org/