This repository implements `@google/design.md`, a CLI tool and programmatic library for a design token format called DESIGN.md. The format pairs YAML frontmatter (tokens) with Markdown prose (rationale). The tool provides validation (lint), diffing, multi-format export (Tailwind v3 JSON, Tailwind v4 CSS, DTCG JSON, CSS custom properties), and spec generation. It is published as an npm package and is designed to be consumed by both human designers and AI coding agents. The architecture is a monorepo with a single CLI package (`packages/cli`) that uses `citty` for command routing. The core pipeline parses DESIGN.md files, builds a token model with reference resolution and color parsing, runs 11 lint rules (including WCAG contrast ratio checks), and emits results via stateless handler functions. A separate spec generation pipeline compiles `spec.mdx` with a custom MDX compiler to produce `docs/spec.md`. The codebase is well-tested with unit tests for each component. Key entry points include the CLI binary (`packages/cli/src/index.ts`), the programmatic `lint()` function (`packages/cli/src/linter/index.ts`), and the spec generator (`packages/cli/src/linter/spec-gen/`). External dependencies are minimal: `citty` for CLI, `zod` for validation, `consola` for logging, and `bun` for build/test. The repository also includes three complete example design systems and a set of agent skills for development workflow.