ECMWF data is usually produced in GRIB format. Older parameters are usually in GRIB1, while more recent parameters and all new parameters are produced in GRIB2.
Trajectory forecasts (tropical cyclones) and time series data are produced in BUFR format.
Data retrieved from MARS can be retrieved in GRIB or NetCDF format. Data disseminated via ECPDS cannot be delivered in alternative formats or converted. GRIB1/GRIB2 data delivered by ECPDS can be separated into separate feeds in the PREd or upon request if you do not have access.
We recommend using ecCodes to manipulate and decode the data. You can also use ecCodes to convert GRIB1 to GRIB2 data or to convert GRIB files to NetCDF files.
See What is the format of the data?
There is also relevant info here for real-time data: File naming convention and format for real-time data
