Use when writing, restructuring, or reviewing any prose documentation — a tutorial, how-to guide, reference page, or explanation/conceptual doc — for a public docs site (e.g. Mintlify MDX, docs/, README material), a getting-started guide, an API/CLI reference page, or a "why we built it this way" conceptual page. Applies the Diátaxis framework (see https://diataxis.fr/) — every document belongs to exactly one of the four quadrants (tutorial / how-to guide / reference / explanation), and mixing quadrants inside one document is the single most common documentation failure. Covers the four-quadrant compass for picking the right form, per-quadrant structure templates, an anti-pattern list for quadrant drift, and generic voice/craft rules — repo-specific voice and target output format (e.g. Mintlify MDX) are resolved from the repo's docs-manifest (falling back to project-context), never hardcoded here.