cdtReader is a Cytoscape 3 app that reads Cluster 3 output files into Cytoscape. When used through the File→Import→Network→File menu, cdtReader will read in CDT files and create all of the nodes in the file and all attribute columns. When used through the Apps→CDTImporter→Import cdt files, cdtReader will input cdt files as well as the corresponding gtr and atr files. If used through the Apps menu, cdtReader will the attribute necessary to visualize the cluster with clusterMaker2's treeView visualization.