How I Use Claude Code and Jira MCP to Modernize Legacy Codebases

Legacy code is the skeleton of every successful company. It runs billing, processes orders, and holds business rules that nobody has fully understood in years. It’s not going anywhere, and that’s exactly why modernizing it matters. For the past several months, I’ve been using Claude Code alongside Jira MCP and a carefully crafted CLAUDE.md to navigate and implement changes in legacy Java codebases. This article is a practical breakdown of that workflow: what it looks like, why it works, and wher