© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. One of the main challenges to implement Industry 4.0 technologies within the industrial fabric is the lack of suitable concrete models and tools that demonstrate the potential benefits of embracing the digital transformation process. To overcome this challenge, over the past years, various Industry 4.0 automation and robotics providers have presented solutions based on visual block programming languages, which follow an emerging low-code approach to reduce the entry barriers of digital technologies. However, block-based low-code tools typically lack the formality introduced by specification languages, limiting their ability to model the industrial processes formally. Taking this into account, in this article, we present the combination of specification languages and visual block programming languages to enable industrial users to test and/or build their own Digital Twin models at a suitable abstraction level and with low entry barriers. In particular, we combine SDL and Snap! to create SDL4Snap!, an opensource and web-based tool that facilitates the implementation and validation of Digital Twin prototypes. Overall, the resulting tool has the potential to reduce the entry barrier to Digital Twins in small and medium enterprises, which are part of the late majority and laggard groups regarding the adoption of digital technologies in the context of Industry 4.0. Peer Reviewed