The HelioSwarm mission (HS) combines data across a multi-spacecraft observatory to probe the dynamics of turbulent near-Earth plasmas (including the pristine solar wind, magnetosheath, and magnetosphere) covering multiple characteristic spatial and temporal scales. In addition to producing ground-breaking science, the HS team intends to be in the forefront of the move to open, reproducible, and reusable processes. In this presentation, we describe our plans for the transparent development of open source data processing and analysis codes for this mission. Consistent with NASA’s Transform to Open Science (TOPS) mission, these open tools and software will facilitate open data and high-quality open results. The techniques of open development, drawn in particular from the established open-source software community, are not applied just to satisfy requirements by “checking the box”. They are demonstrated engineering tools that enable the creation and maintenance of high quality software and systems in a manner responsive to mission and scientific needs. In particular, we discuss our prioritization of effort and context-sensitive approaches given the wide range of users for mission-maintained software, from flight through ground software to data production and analysis. We also discuss plans for code reuse between data processing and analysis to ensure consistency of results while allowing maximum flexibility in analysis.