Checking price indices (“validation”) is considered to be an important step that is carried out each month before inflation figures (CPI) are published. The aim is to analyse and decompose price indices in a top-down way, such that the main contributors to overall price change are identified. We propose the use of time series modelling and forecasting for higher product aggregates. More detailed aggregates are analysed with index decomposition methods, which yield detailed product contributions. First results for a prototype tool show its efficiency, which is important now the CPI makes greater use of large transaction and web scraped datasets.