Developer experience (DX) is a decisive coefficient both for the performance of developers and for keeping developers actively contributing to software platforms. When it comes to understanding what affects DX in software platforms, researchers and practitioners recognize several factors. This topic still lacks a roadmap regarding the main DX factors, primarily when considering platforms in software ecosystems. Thus, this study aims to investigate and characterize the factors that affect DX in software platforms. After investigating the literature, we selected 35 studies to analyze the state-of-the-art of DX in development on software platforms. As the main contribution, we provided a set of factors organized into six categories that affect DX in software platforms. This set of DX factors can be used as a reference guide to support researchers and practitioners in improving the development processes of the products and services on software platforms.