a50 - a simple tool for graphing genome coverage and fragmentation. Reads files of contigs, and compares them by plotting each as a line in a graph. The x-axis represents contig number, the y-axis represents total (cumulative) size. An ideal assembly contains a few, large contigs, thus this curve should rise steeply, and stop early (but at the expected genome size). Conversely, a poor assembly consisting of many small fragments will have a less steep curve extending far to the right. The graphs produced by a50 gives a simple and easy to grasp comparison between assemblies, and yet produces a more detailed and informative view than the usual metrics like largest contig size or N50. The Darcs repository is at <http://malde.org/~ketil/biohaskell/a50>.