Background: Visual Analogue Scale (VAS) is a validated tool to assess control in allergic rhinitis patients. Objective: The aim of this study was to validate the use of VAS in the MASK-rhinitis (MACVIA-ARIA Sentinel NetworK for allergic rhinitis) app (Allergy Diary) on smartphones screens to evaluate allergic rhinitis symptoms and disease control. Methods: Each user filled 4 different VAS measuring overall, nasal, ocular, and asthma symptoms at least once. Following COSMIN guidelines, we evaluated internal consistency, (Cronbach's alpha coefficient and test-retest), reliability (intraclass correlation coefficients), sensitivity, and acceptability of the MASK-Rhinitis VAS. Results: Between 1 August 2015 and 31 July 2016, the app was used 14 612 times in 15 countries. A total of 1225 users used it more than once, during the evaluated period. The tool resulted to be statistically satisfactory, showing excellent internal consistency (Cronbach's test > 0.84, test-retest > 0.7), reliability (>0.9), and acceptability. In addition, the tool had a good sensitivity when users (n = 521) answered the VAS twice in less than 3 hours. Conclusions and Clinical Relevance: The MASK-rhinitis VAS is a reliable and valid tool to assess allergic control on smartphone screens, at the population level.