d3‑hexjson is a lightweight D3 plugin that converts data encoded in the Open Data Institute’s HexJSON format into ready‑to‑draw hexagonal maps. It supplies functions to compute hex positions, sizes, vertex strings, background grids and boundary lines, letting developers quickly render interactive hexmaps (e.g., constituency maps, statistical grids) with standard D3/SVG workflows. The library is aimed at web developers and data visualisers who need to display spatial data as hexagonal cartograms.