COBOL forms the backbone of the global economy, with more than 220 billion lines of code supporting nearly 70% of all business transactions worldwide. But the ecosystem faces a serious skills crisis: a large proportion of experienced COBOL programmers are nearing retirement, while universities have largely removed the language from their curricula. At the same time, traditional COBOL tools rooted in 1980s-era workflows fail to appeal to a new generation of developers raised on modern, interactive environments. To address this gap, we developed COBook, a notebook-based environment that brings modern interactive tooling to COBOL development and learning. COBook is one of the first tools to integrate these capabilities for COBOL in a notebook environment. COBook makes the program structure visible through visualizations, including flowcharts, data flow diagrams, and memory layouts, which may help learners build mental models of COBOL programs. Its AI-Assisted features include plain-language explanations, error suggestions, and code generation to support learners working with unfamiliar COBOL syntax. In a preliminary evaluation with 33 novice programmers across five COBOL comprehension tasks, COBook reduced mental demand by 53%, physical demand by 42%, temporal demand by 38%, and frustration by 59%, while improving perceived performance by 91% and simplifying the handling of logic complexity by 53% compared to traditional text-based COBOL IDE programming. By bridging the gap between legacy systems and modern tooling, COBook aims to make COBOL more accessible and engaging for today's programmers. The tool demo video is available at https://youtu.be/kjdzJsCq_Lc, the tool website and the artifacts are at https://github.com/rishalab/COBook.

@inproceedings{PappuPC26,
  title = {COBook: An AI-Assisted Interactive COBOL Notebook with Visualization},
  author = {Raghavendra Pappu and Satish Pati and Sridhar Chimalakonda},
  booktitle = {FSE},
  year = {2026},
  doi = {10.1145/3803437.3806430}
}