K-Saju Crew Feature Uses Temporary State to Cast Friend Groups as K-Pop Acts

K-Saju, an entertainment web app inspired by saju astrology, launched a '/crew' feature that lets friend groups see themselves cast as a K-Pop group based on their birth dates. A creator shares a link, each friend enters their own birth date, and the app assigns K-Pop roles and shows pairwise chemistry for groups of three to seven members. The engineering challenge was handling shared group input without permanently storing user data, so the team built a hybrid approach: a temporary lobby stored in a JSON file that expires after 30 days. Once a group is complete, the result is converted into a stateless permalink that encodes all inputs in the URL, allowing the page to be reproduced without any server-side record. The team acknowledges a privacy trade-off, noting that birth dates and nicknames are visible in the share link, but the server does not retain personal data after the lobby expires.