Mutations in DNA, the genetic blueprints for every living organism, are the basis for evolution and adaptation. However, the vast majority of mutations are harmful, and organisms across the tree of life use error-checking mechanisms to minimize the number of DNA mutations that occur. Unfortunately, errors in transcription, the mechanism used to read the DNA encoded in genes and thereby express them, occur at rates that are thousands of times higher than the DNA mutation rate. This means that the genes that the cell works so hard to preserve from mutations will not be correctly read much of the time. Just how frequent do these transcription errors occur? Chuck Traverse tells us about his work, which uses a recently developed DNA-sequencing technique to measure the error rate of transcription in multiple bacterial species.