The Open Procurement Contracting is plugin to Open Procurement API software.
REST-ful interface to plugin is in line with core software design principles.
This plugin conventions follow the Open Procurement API conventions.
API is highly unstable, and while API endpoints are expected to remain relatively stable the data exchange formats are expected to be changed a lot. The changes in the API are communicated via Open Procurement API maillist. Questions can be asked via Gitter.