The ECMWF GRIB-API is an application program interface accessible from C, FORTRAN and Python programs developed for encoding and decoding WMO FM-92 GRIB edition 1 and edition 2 messages. A useful set of command line tools is also provided to give quick access to GRIB messages.
The latest version of GRIB edition 2 documents from the WMO can be accessed HERE
Starting from version 2.0.0, ecCodes is the primary GRIB encoding/decoding package used at ECMWF. Any new features for the handling of GRIBs will be only developed in ecCodes. Nevertheless GRIB-API will be maintained and new releases made publicly available (until the end of 2018) to support decoding of ECMWF model output. Replacing GRIB-API with ecCodes is expected to be transparent for current GRIB-API users. In particular the "grib_" functions are included in the ecCodes library.
Users are strongly advised to start the migration process.
Please note that GRIB-API support is being discontinued at the end of 2018.