(E)-4-((4-amino-3-methylphenyl)diazenyl)-3-methylphenol is an azo dye used in the production of colored textiles and inks, providing bright and stable coloration, often in yellow to brown shades. Commonly applied in the coloring of cotton, wool, and silk fabrics, with color intensity and shade controllable by pH adjustments during dyeing. Also utilized in histological staining for microscopic examination of tissue samples. Serves as a pH indicator due to its color-changing properties in different acid-base environments. Occasionally employed in research settings for coupling reactions in organic synthesis.