BACKGROUND: Children with autism spectrum disorder (ASD) exhibit atypical responses to sensory stimuli. These sensory and perceptual issues persist as hyper-, hypo-, or atypical sensory reactivity that impacts their daily activities. The present protocol describes a method for developing a locally relevant and simple instrument for identifying and estimating the severity of sensory reactivity in children with ASD. NOVELTY: Employing a consultative approach, the authors aim to develop and validate an Indian instrument to assess sensory reactivity in children with ASD. OBJECTIVES: To gather insights from parents and experts about sensory reactivity patterns in children with ASD and to use this information to create and validate a culturally relevant tool for measuring the severity of sensory reactivity in these children. METHODS: This study will be conducted in two phases following an exploratory sequential mixed-method design. In the first phase, data will be collected through in-depth interviews of parents of children with ASD and focused group discussions with the experts. The collected data will be used to identify different themes and domains related to sensory reactivity. A questionnaire will be developed based on their inputs. In the second phase, the instrument will be analyzed further using exploratory factor analysis to obtain the factor structure and confirmatory factor analysis to test the factor structure of the developed instrument. EXPECTED OUTCOME: A simple, reliable, and validated severity instrument will be developed for children with ASD and made accessible to all for convenient use.