How to Write a Claude System Prompt That Actually Ships

A single 25-word constraint added to Claude Code's system prompt on April 16, 2026 caused a 3% drop in benchmark intelligence - confirmed by Anthropic's official postmortem. Proper section ordering (role to constraints to format to examples) reduces out-of-schema responses by 23%. This article breaks down the 9-section template behind every Claude system prompt that ships in production, with 5 real-shape examples showing how the pattern bends to different jobs.