D3.js & Observable Plot

D3.js (Data-Driven Documents) is the library behind virtually every bespoke interactive data visualisation on the web. Created by Mike Bostock and now maintained by Observable, it provides low-level primitives for binding data to DOM elements and applying data-driven transformations — giving you complete control over every pixel. Observable Plot, also from the same team, is the higher-level sibling: a concise API for creating statistical charts (scatterplots, bars, lines, areas, heatmaps) in just a few lines of code, designed for exploratory analysis. Together, they span the full spectrum from quick data exploration to polished, interactive narrative visualisations. Both are free, open-source, and widely used by newsrooms (including Indian data journalism teams), researchers, and civic technologists.