**Abstract**

Cytotoxicity experiments are carried out to evaluate whether a chemical has cytotoxic potential. Because of its ease of use and compatibility with data collected from *in vivo* investigations, cell-based cytotoxicity studies have emerged as a viable alternative to animal trials in research. Cell-damaging events such as apoptosis, autophagy, and necrosis may occur after exposure to cytotoxic substances. Thanks to the cell-based cytotoxicity studies, basic information is obtained about the cytotoxic effects of the tested substance. To measure cell viability, a variety of techniques are used. Regardless of the sort of cytotoxicity investigation that was carried out, the crucial thing is to figure out how much metabolic activity there is in the cells at the end of the experiment. Cytotoxicity detection methods are generally colorimetric, luminescent, and enzymatic methods. In colorimetric methods, measurement is based on color change using tetrazolium salts, such as MTT, MTS, XTT, WST. Three main steps are followed in tetrazolium compound toxicity tests. Toxic compounds are introduced to cells in the initial stage. The poisonous chemical is eliminated in the second phase and followed by the addition of the tetrazolium compound. The metabolically active cells are determined in the last stage by using a spectrophotometric approach to measure color change.

**Keywords:** cytotoxicity, colorimetric assay, formazan, *in vitro*, metabolic activity
