# Cursor Rules for Tailwind CSS and shadcn/ui > Cursor rules that enforce Tailwind v4 conventions and shadcn/ui component patterns, preventing agents from reinventing primitives that already exist. **Type:** Rule **Tools:** Cursor **Stack:** Next.js, TypeScript, Tailwind **Updated:** 2026-06-08 --- Paste this into `.cursor/rules/tailwind-shadcn.mdc` (or your project-level Cursor rules file). Cursor loads all `.mdc` files in `.cursor/rules/` automatically on project open. ## Cursor Rules File ```txt title="Cursor Rules" # Tailwind CSS + shadcn/ui Rules ## Tailwind conventions - Use Tailwind CSS v4. Class names follow the v4 API — do NOT use deprecated v3 class names (e.g. use `shadow-sm` not `drop-shadow-sm` for box shadows on elements). - All utility classes must be static strings so Tailwind's content scanner can detect them. Never build class names with string concatenation or template literals unless the full class name is in the source (e.g. `bg-${color}` is forbidden; use a lookup object instead). - Class order: layout → box model → typography → visual (bg, border, shadow) → interactive (hover, focus) → responsive breakpoints. Use `prettier-plugin-tailwindcss` to enforce this automatically — do not manually reorder. - Never write custom CSS for spacing, color, or typography that can be expressed with a Tailwind utility. Custom CSS lives in `src/styles/` and must be justified by a comment. - Use `cn()` from `@/lib/utils` to merge conditional classes. Never use `clsx` or `classnames` directly elsewhere — they are already re-exported from `cn()`. ## shadcn/ui conventions - Before creating a new UI component, check `src/components/ui/` for an existing shadcn/ui primitive. Use it. Do not re-implement Button, Dialog, Input, Select, Tooltip, or any other component that shadcn already provides. - Add new shadcn components with `npx shadcn@latest add ` — never copy-paste component source manually from the docs. - Extend shadcn components by wrapping them, not by editing the file in `src/components/ui/` directly. Edits there are overwritten by future `shadcn add` runs. - Use shadcn's `variant` and `size` props before adding className overrides. If a new variant is needed, add it to the component's `cva()` definition in `src/components/ui/`. - Dark mode is handled by the `dark` class on ``. Never use `prefers-color-scheme` media queries alongside shadcn — they conflict with the class strategy. - Do not install `@radix-ui/*` packages directly. They are transitive dependencies of shadcn components; adding them directly risks version mismatches. ## Accessibility - Every interactive shadcn component must have an accessible label. Use `aria-label`, `aria-labelledby`, or a visually-hidden `` — never omit it. - Icon-only buttons must include `Description`. ## Definition of done - `bun run build` completes without Tailwind class warnings. - No `className` strings contain dynamic concatenation (`bg-` + variable). - No new Radix packages in `package.json` that aren't installed via `shadcn add`. - Storybook (if present) renders the new/modified component without console errors. ``` ## Why these rules - **"Check `src/components/ui/` before creating anything"** is the single highest-value rule for shadcn projects. Agents default to writing bespoke components — a custom `