Context: Interest in diversity in software development has significantly increased in recent years. Reporting on diversity in software projects can enhance user trust and assist regulators in evaluating adoption. Recent AI directives include clauses that mandate diversity information during development, highlighting the growing interest of public regulators. However, current documentation often neglects diversity in favor of technical features, partly due to a lack of tools for its description and annotation. Objectives: This work introduces the Software Diversity Card, a structured approach for documenting and sharing diversity-related aspects within software projects. It aims to profile the various teams involved in software development and governance, including user groups in testing and software adaptations for diverse social groups. Methods: We conducted a literature review on diversity and inclusion in software development and analyzed 1,000 top-starred Open Source Software (OSS) repositories on GitHub to identify diversity-related information. Moreover, we present a diversity modeling language, a toolkit for generating cards using it, and a study of its application in two real-world software projects. Results: Despite the growing awareness of diversity in the research community, our analysis found a notable lack of diversity reporting in OSS projects. Applying the card to real-world examples highlighted challenges such as balancing anonymity and transparency, managing sensitive data, and ensuring authenticity. Conclusion: Our proposal can enhance diversity practices in software development, support public administrations in software assessment, and help businesses promote diversity as a key asset.