The Climate Model Output Rewriter (CMOR) was originally developed to help modeling groups contributing to CMIP to prepare simulations in accordance with the CMIP data conventions. In preparation for CMIP6, the latest version (CMOR3) was improved to facilitate the preparation of gridded observations, and thus CMOR is now sometimes referred to as the Climate Model and Observations Rewriter (CMOR). All obs4MIPs compliant gridded products are prepared by CMOR to ensure technical alignment between CMIP and obs4MIPs.