Context: Software development benefits from having Boundary Artefacts (BAs), as a single artefact can supply stakeholders with different boundaries, facilitating collaboration among social worlds. When those artefacts display inconsistencies, such as incorrect information, the practitioners have decreased trust in the BA. As trust is an essential factor guiding the utilisation of BAs in software projects, it is necessary to understand which principles should be observed when creating them. Objective: This study aimed at develop and validate a preliminary guideline support the creation of trustworthy BAs. Method: We followed a multi-step approach. We developed our guideline through a literature review and previous results from our case study. Second, we submitted the guideline for an expert evaluation via two workshops and a survey. At last, we adjusted our guideline by incorporating the feedback obtained during the workshops. Results: We grouped the principles collected from a literature review into three categories. The first category (Scope) focuses on the scope, displaying principles referring to defining each boundary's target audience, needs, and terminology. The second category (Structure) relates to how the artefact's content is structured to meet stakeholders' needs. The third (Management) refers to principles that can guide the establishment of practices to manage the artefact throughout time. The expert validation revealed that the principles contribute to creating trustworthy BAs at different levels. Also, the relevance of the guideline and its usefulness. Conclusions: The guideline strengthen BA traits such as shared understanding, plasticity and ability to transfer. Practitioners can utilise the guideline to guide the creation or even evaluate current practices for existing BAs.