RCL-tdTomato mice are generated via genome editing to knock the CAG-LSL-tdTomato cassette into the ROSA26 safe harbor locus. Upstream of the tdTomato gene lies a loxP-Stop-loxP (LSL) cassette, which blocks the transcription and expression of tdTomato. Upon Cre recombination, cells expressing Cre recombinase (and their future cell lineages) exhibit strong tdTomato fluorescence. This model is suitable for validating Cre mice with high recombination efficiency and potential expression leakage, as well as for other cell lineage tracing applications.