[luodaint]

As a result of shipping a working product for six months with Claude Code integrated into SaaS production, the only surviving constraints had all been less than 50 lines: migrations' generation vs execution conventions, authentication flow invariants, internationalization setup rules. Any longer constraints would get either selectively ignored or cause confusion when starting sessions.

The important distinction: CLAUDE.md will not explain how the model understands your architecture. Rather, it will prevent certain kinds of regression from happening. "Never create a user without calling the workspace provision step" is the right constraint. "This is how our entire system works" is not – the model learns it from the codebase.

The mistake is writing constraints based on an architecture constructed with slop. The sequence is important here.