  We present a description of our numerical code BLAZAR. This code calculates
spectra and light curves of blazars during outbursts. The code is based on a
model in which the non-thermal flares in blazars are produced in thin shells
propagating down a conical jet with relativistic velocities. Such shells may
represent layers of a shocked plasma, enclosed between the forward and reverse
fronts of an internal shock. In the model adopted by us, the production of
non-thermal radiation is assumed to be dominated by electrons and positrons
which are accelerated directly, rather then injected by pair cascades. The code
includes synchrotron emission and inverse-Compton process as the radiation
mechanisms. Both synchrotron photons and external photons are included as the
seed photons for Comptonization. At the present stage, the code is limited to
treat the inverse Compton process only within the Thomson limit and is
specialized to model radiation production in the flat spectrum radio quasars.
As an example, we present the results of modeling an outburst in 3C 279 - the
most extensively monitored gamma-ray - bright quasar.
