In this work, we discovered that coumarin-30, a widely commercially available bright laser dye, associates with the colchicine site of tubulin. Its fluorescence is enhanced by about an order of magnitude upon binding to tubulin. Coumarin-30 fluorescence is dramatically brighter than colchicine's, and both its excitation and emission peaks are in the visible spectrum, making it an excellent tubulin probe, compatible with many standard fluorescence-based detection methods and tools. By combining coumarin-30 with the MST technique, we have developed a rapid and costeffective 'C-MST' assay for identification of small molecule drugs that bind to diverse sites on tubulin. In addition, the assay has the built-in capacity to discriminate colchicine site binders from other types of ligands.