Leptons, b-tagging and MET reconstruction at CMS after the first data

The performance of reconstruction and analysis tools is an essential ingredient for top quark physics analyses. This presentation gives an overview of the current tools in the CMS experiment, their expected performance obtained with simulations and the performance studies using the first data. The presented data consists of several data taking campaigns. The Cosmic Run at Four Tesla (CRAFT08/09) provided millions of cosmic muons and was primarily used to study the tracker and the muon systems. In the first weeks after the start of the LHC experiment at the end of 2009, proton collision data at a center of mass energy of 900 GeV and 2360 GeV were collected. During the first months of 2010 data at a center of mass energy of 7 TeV was collected. During the redaction of this note data taking at 7 TeV is ongoing.