  The Core Cosmology Library (CCL) provides routines to compute basic
cosmological observables to a high degree of accuracy, which have been verified
with an extensive suite of validation tests. Predictions are provided for many
cosmological quantities, including distances, angular power spectra,
correlation functions, halo bias and the halo mass function through
state-of-the-art modeling prescriptions available in the literature. Fiducial
specifications for the expected galaxy distributions for the Large Synoptic
Survey Telescope (LSST) are also included, together with the capability of
computing redshift distributions for a user-defined photometric redshift model.
A rigorous validation procedure, based on comparisons between CCL and
independent software packages, allows us to establish a well-defined numerical
accuracy for each predicted quantity. As a result, predictions for correlation
functions of galaxy clustering, galaxy-galaxy lensing and cosmic shear are
demonstrated to be within a fraction of the expected statistical uncertainty of
the observables for the models and in the range of scales of interest to LSST.
CCL is an open source software package written in C, with a python interface
and publicly available at https://github.com/LSSTDESC/CCL.
