The Sister City Transparency Act directs the Comptroller General to study sister city partnerships between U.S. communities and foreign cities in countries with significant corruption problems, specifically those scoring 45 or below on Transparency International's 2019 Corruption Perceptions Index. The study will examine how foreign communities select U.S. partners, what activities occur in these partnerships, the economic and educational outcomes, and whether adequate safeguards exist against foreign espionage, economic coercion, and misuse of visa programs. The Comptroller General must also assess the transparency of these partnerships' contracts and activities, potential vulnerabilities to malign foreign influence, and recommend best practices for oversight and disclosure. The bill requires a report within six months of the study's initiation to be submitted to relevant congressional committees overseeing foreign affairs, armed services, and education. This legislation contains no specific funding authorization or implementation timeline beyond the six-month reporting deadline.