The invention relates to methods, compositions and kits for labelling and detecting endonuclease-treated cells, and most preferably eukaryotic cells.rnrnThe CRISPR-barcoding system could be used as an alternative tool to the classical lentiviral DNA barcode libraries, ensuring the detection of thousands of distinct barcodes through qPCR or deep-sequencing.rnrnThis barcoding approach enables tracing of the mutated cells immediately after DNA editing without the need to derive clones, thus providing a unique means to investigate the effects of different kinds of genomic modifications, regardless of their potential impact on cell growth, in a broad range of functional assays.rnrnThis strategy represents a high-resolution tracking of single specific cancer cells allowing to identify even rare pre-existing resistant subclones potentially involved in mechanisms of acquired resistance to therapy. The main proofs of concept reported are related to cancer models, nevertheless this technology can be implemented in different fields of biological research.