Brief is a SKILL.md-based prompt system designed for serious marketing work: writing copy, planning campaigns, and critiquing landing pages. It uses a lightweight router that dispatches to 9 deep-dive reference modules, so responses stay focused without front-loading every instruction at once. Two quality gates prevent the model from guessing when key context is missing — it asks instead. A universal quality bar enforces specificity, reader-first framing, single-message discipline, proof over claims, and honesty throughout. The package ships with a 26-prompt evaluation suite and raw benchmark outputs showing a 20-percentage-point improvement over baseline. Works with any tool that can load a SKILL.md file.