People with the genetic trait of synaesthesia experience phantom colours, sounds, tastes, and other unusual sensations. These are triggered by everyday activities like reading or listening to music. Importantly, synaesthesia is comorbid with health conditions including anxiety disorder and autism, and has a known impact on education. Although there are widely available tests for diagnosing synaesthesia in adults, there are none for children - despite its relatively wide impact (307 million synaesthetes worldwide). My ERC Consolidator grant MULTISENSE has generated such a test, to share with fellow researchers. However, during the course of MULTISENSE we have been approached by multiple professionals beyond the research sector (e.g. clinicians), each in need of a diagnostic for the child synaesthetes they are increasingly encountering. These professionals require a test package comprising Diagnostic tool, Testing manual, Automatic Scoring, etc. which could be easily implemented by non-scientists. Not only is this testing package non-existent in any country worldwide, but it is requested from us on a regular basis. Hence, SYN-TOOLKIT will provide an app-based package to diagnose and support two of the most prevalent forms of childhood synaesthesia. We will trial our package on target audiences including partners in Local Education Authorities (with government oversight of schools) and the National Health Service. We will take our test-package to proof of concept by establishing technical feasibility, usability, and commercialisation. We have explored our market with an award that engaged the Sussex Innovation Centre, experts in market exploration. In summary, there is a pressing need to produce a commercialised test kit for childhood synaesthesia, for use by clinicians, education professionals and parents. This would address the striking lack of provision for children with synaesthesia, bringing benefits to synaesthetes, parents, educators, and clinical practice.