Most reports about Spec-Driven Development come from greenfield demos or small projects. This session draws on two years of modernizing large Java business applications with a spec-driven approach, moving them from Swing and Eclipse RCP to the web. These projects involve multiple teams, legacy systems, and various departments.

The session covers four questions. How should specifications be written so that an agent delivers usable code? How much of the generated code needs review, and where is the effort worthwhile? What do skills and MCP servers add in practice? And where does the approach reach its limits?

The talk includes a walkthrough of one real specification and the code an agent produced from it, plus examples of specifications that did not work. Examples come from ongoing projects built with Vaadin and jOOQ. The experiences apply to other Java or web stacks as well.