The UPSC Mains Examination differs significantly from the Preliminary Examination in terms of structure and purpose. While the Prelims serves as a screening test focusing on general studies and optional subjects, the Mains evaluates in-depth knowledge through descriptive answers across multiple papers. The Mains also includes a personality test, assessing personal attributes and suitability for civil services. This comprehensive evaluation helps examine the candidates' analytical thinking, understanding of complex issues, and command over the subjects.