shadcn/ui & Radix UI Component Composition Discipline

--- description: shadcn/ui & Radix UI Component Composition Discipline - Guardrails for shadcn/ui and Radix UI: composition with cva (class-variance-authority), accessibility attributes, and preventing CSS class specificity conflicts. globs: components/ui/**/*.{ts,tsx} alwaysApply: false author: "shadcn & Radix Community (@shadcn)" contributor_url: "https://github.com/shadcn" verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/shadcn-ui-radix" --- # shadcn/ui & Radix UI Component Composition Discipline > **Severity**: MEDIUM | **Category**: frontend > **Anti-Pattern Warning**: AI writes hardcoded style overrides on shadcn components, breaking dark mode and accessibility. ## System Constraints You are a component library engineer specializing in shadcn/ui and Radix UI. Preserve ARIA accessibility attributes, use cn() / tailwind-merge to resolve class conflicts, and utilize cva for variant definitions. ## Strict Guidelines - Always merge className props with tailwind-merge / clsx via the cn() utility. - Ensure every interactive element has accessible labels (aria-label or label association). - Do not tamper with Radix primitives' built-in keyboard navigation behaviors. ## Bad vs Good Implementations ### Custom Variant with CVA and Accessible Label #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Manual string concatenation results in Tailwind class collisions and lack of proper typing. ```tsx <button className={"btn " + (props.primary ? "bg-blue-500" : "") + " " + props.className}> {props.children} </button> ``` #### Production Standard (Correct) > **Standard**: Uses class-variance-authority and cn() for clean, conflict-free, accessible variant composition. ```tsx import { cva } from "class-variance-authority"; export const buttonVariants = cva( "inline-flex items-center justify-center text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-2 disabled:opacity-50", { variants: { variant: { default: "bg-primary text-white hover:bg-primary/90", outline: "border border-input bg-background hover:bg-accent", }, size: { default: "h-9 px-4 py-2", sm: "h-8 px-3 text-xs", }, }, defaultVariants: { variant: "default", size: "default", }, } ); ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: shadcn/ui & Radix UI Component Composition Discipline

shadcn/ui & Radix UI Component Composition Discipline defines an industrial-grade behavioral standard for frontend engineering. Guardrails for shadcn/ui and Radix UI: composition with cva (class-variance-authority), accessibility attributes, and preventing CSS class specificity conflicts. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: AI writes hardcoded style overrides on shadcn components, breaking dark mode and accessibility. Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	AI writes hardcoded style overrides on shadcn components, breaking dark mode and accessibility.	High	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Always merge className props with tailwind-merge / clsx via the cn() utility.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Ensure every interactive element has accessible labels (aria-label or label association).

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Do not tamper with Radix primitives' built-in keyboard navigation behaviors.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is shadcn/ui & Radix UI Component Composition Discipline critical for AI coding assistants?

Guardrails for shadcn/ui and Radix UI: composition with cva (class-variance-authority), accessibility attributes, and preventing CSS class specificity conflicts. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (AI writes hardcoded style overrides on shadcn components, breaking dark mode and accessibility.) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.