Why Your CLAUDE.md Is Making Claude Worse, and the Prompt That Audits It

Anthropic removed over 80 percent of Claude Code's system prompt for the Claude 5 generation and measured no loss on their coding evaluations. Their explanation was blunt: they had been over-constraining Claude Code, through the system prompt and through their own CLAUDE.md files and skills. When they read back real transcripts they found single requests carrying instructions that contradicted each other, one telling Claude to leave documentation as appropriate and another telling it not to add comments.

Your setup has the same problem for the same reason. Every rule you wrote was written for a model that needed it. Most of them were written for models that are two generations old. On Opus 5 they are not guardrails any more, they are noise the model has to read, weigh and resolve before it does anything.

This guide is what actually changed, how to tell which of your rules still earn their place, and a prompt you can paste into Claude that does the audit for you.

• Verified: Anthropic cut over 80 percent of Claude Code's system prompt, announced 24 July 2026
• Their word for the old approach: over-constraining
• The fix is not deleting everything. It is keeping the small number of rules that still bind.