  A common problem in particle physics is the requirement to reproduce
comparisons between data and theory when the theory is a (general purpose)
Monte Carlo simulation and the data are measurements of final state observables
in high energy collisions. The complexity of the experiments, the obervables
and the models all contribute to making this a highly non-trivial task.
  We describe an existing library of Fortran routines, HZTool, which enables,
for each measurement of interest, a comparable prediction to be produced from
any given Monte Carlo generator. The HZTool library is being maintained by
CEDAR, with subroutines for various measurements contributed by a number of
authors within and outside the CEDAR collaboration.
  We also describe the outline design and current status of a replacement for
HZTool, to be called Rivet (Robust Independent Validation of Experiment and
Theory). This will use an object-oriented design, implemented in C++, together
with standard interfaces (such as HepMC and AIDA) to make the new framework
more flexible and extensible than the Fortran HZTool.
