A CLAUDE.md for Legacy Code That Actually Works

Free checklist (12 checks + a fill-in CLAUDE.md template): https://legacy2latest.kit.com/83f5e476d0 A CLAUDE.md that describes your project is not enough on legacy code. Here is the 36-line CLAUDE.md we used to take a legacy demo service from Spring Boot 2.7 / Java 11 to Spring Boot 4.1 / Java 25 with Claude Code: commands, rules a reviewer can check, and a definition of done that points at evidence. Plus the moments in the real session transcripts where Claude followed it, and where a rule was not enough. How a senior engineer reviews the diff that comes out of it:    • How a Senior Engineer Reviews AI-Generated...   The six mistakes Claude Code made during this upgrade:    • Claude Code Made 6 Mistakes on Legacy Code...   Chapters 00:00 Why a descriptive CLAUDE.md isn't enough 00:35 The CLAUDE.md that doesn't help 00:58 Landmines nobody wrote down 02:07 The 36-line CLAUDE.md, line by line 04:17 Claude following the contract 05:02 47 tests in the build, 56 in the report 05:46 A rule used as a reason 06:05 Treat CLAUDE.md like code 06:23 Five facts worth knowing 07:19 Write yours in twenty minutes 07:51 Wrap-up and next video Every Claude Code session in this video is a real run, replayed from its transcript. The screen parts are narrated with a clone of my own voice. The intro and the outro are filmed. I'm Daniel, a senior full-stack engineer. Views are my own. #ClaudeCode #CLAUDEmd #AICoding