Diffusion is the process that lets the color spread through tea, but there is way more to it than that: It’s also one of the most fundamental principles underlying the inner workings of living cells. The ability of molecules to move in or between cells determines where—and if—they can carry out their function. Consequently, the motility of molecules can reveal a lot about their tasks in the living organism. Scientists are therefore using so-called “FRAP” assays (FRAP: Fluorescence Recovery After Photobleaching) to investigate diffusion kinetics, a method established more than 40 years ago. The interdisciplinary team around Patrick Müller at the Friedrich Miescher Laboratory of the Max Planck Society in Tübingen, Germany, had a new take on this kind of experiment. In the journal Nature Communications they call attention to the limitations of pre-existing analysis tools for FRAP assays—and offer a flexible and accurate alternative: their open-access software “PyFRAP”.