Nylund, KaiMankoff, JenniferPotluri, VenkateshAigner, WolfgangAndrienko, NataliaWang, Bei2025-05-262025-05-2620251467-8659https://doi.org/10.1111/cgf.70119https://diglib.eg.org/handle/10.1111/cgf70119We present MatplotAlt, an open-source Python package for easily adding alternative text to Matplotlib fgures. MatplotAlt equips Jupyter notebook authors to automatically generate and surface chart descriptions with a single line of code or command, and supports a range of options that allow users to customize the generation and display of captions based on their preferences and accessibility needs. Our evaluation indicates that MatplotAlt's heuristic and LLM-based methods to generate alt text can create accurate long-form descriptions of both simple univariate and complex Matplotlib fgures. We fnd that state-of-the-art LLMs still struggle with factual errors when describing charts, and improve the accuracy of our descriptions by prompting GPT4-turbo with heuristic-based alt text or data tables parsed from the Matplotlib fgure.Attribution 4.0 International License10.1111/cgf.7011912 pages