There is need and opportunity for assessments that support quick and playful--yet also accurate, rigorous and developmentally sensitive--appraisals of early numeracy. Ideally, these should be accessible to those who have opportunity to support children's learning development and ultimately shift children's trajectories. The iPad-based "Early Years Toolbox (EYT) Early Numeracy" assessment was developed and evaluated to determine its validity and reliability, and appropriateness of use by researchers and preschool educators. Results from two studies with 246 children aged 3-5 years indicated the following: construct validity and internal consistency, concurrent validity with established measures, developmental sensitivity, test--retest reliability and highly comparable results whether used by a researcher or an educator. This yields a brief and playful assessment of early numeracy and a potential approach to develop broad-use early years assessments.