In organic chemistry, indoxyl is a nitrogenous substance with the chemical formula: C8H7NO.

[1][2] Indoxyl is isomeric with oxindol and is obtained as an oily liquid.

The Heumann indigo synthesis starts from anthranilic acid: In nature indoxyl is derived from indican, which is a glycoside.

Indigo dye is a product of the mild oxidation of indoxyl.

Indoxyl can be found in urine and is titrated with Obermayer's reagent, which is a dilute solution of ferric chloride (FeCl3) in hydrochloric acid (HCl).