  We present an event-file format for the dissemination of
next-to-leading-order (NLO) predictions for QCD processes at hadron colliders.
The files contain all information required to compute generic jet-based
infrared-safe observables at fixed order (without showering or hadronization),
and to recompute observables with different factorization and renormalization
scales. The files also make it possible to evaluate cross sections and
distributions with different parton distribution functions. This in turn makes
it possible to estimate uncertainties in NLO predictions of a wide variety of
observables without recomputing the short-distance matrix elements. The event
files allow a user to choose among a wide range of commonly-used jet algorithms
and jet-size parameters.
  We provide event files for a $W$ or $Z$ boson accompanied by up to four jets,
and for pure-jet events with up to four jets. The files are for the Large
Hadron Collider with a center of mass energy of 7 or 8 TeV.
  A C++ library along with a Python interface for handling these files are also
provided and described in this article. The library allows a user to read the
event files and recompute observables transparently for different pdf sets and
factorization and renormalization scales.
