The RCADO Framework for Frontend System Design Interviews

When you walk into a frontend system design interview, you’re expected to do more than list APIs or throw boxes on a diagram — you’re expected to demonstrate how you think in a modern UI framework.

Interviewers increasingly care about how you structure components, manage state, and design data flow, not just backend-inspired abstractions.

The RCADO Framework is a modern evolution of the traditional RADIO framework—tailored specifically for frontend engineers who build real UI systems.

It stands for:

Why RADIO → RCADO: The Shift in Focus

The necessity for RCADO was inspired by key feedback from experienced frontend engineers who found the traditional approach often missed the mark in specialized UI design rounds. The problem with applying RADIO directly to frontend system design isn't the framework itself, but its focus.

“I realized I was failing multiple frontend system design interviews — even though I used RADIO perfectly. The core issue wasn't the framework; it was the emphasis. RADIO naturally guides you toward backend-style thinking — APIs, interfaces, controllers — but in frontend rounds, interviewers are truly focused on just two things:
1. What components exist and what props they take and
2. How state is managed and which component owns it.

Once I replaced Interface with Components and dropped Controller entirely, my conversation flow immediately improved. I’d start with Requirements, then instantly dive into the component tree, state ownership, and data flow. The results were night and day — the same interviews turned into strong passes.”

— L5 Frontend Engineer (Facebook), via Reddit

This valuable observation reshaped how many successful frontend engineers now approach design rounds. Instead of treating UI systems like backend diagrams, RCADO makes the discussion framework-native — focusing on component architecture, data flow, and user-facing pillars like performance, accessibility, and security.

It’s not just a tweak — it’s the natural evolution of RADIO for modern frontend interviews.

R – Requirements

As before, this is your foundation. Without understanding what to build, you’ll end up optimizing the wrong thing. Always start here.

Functional Requirements

Clarify what exactly you’re building:

• What’s the scope? (e.g., Feed, Form, Dashboard)
• What features are expected? (e.g., CRUD, Search, Filtering)
• What user actions should be supported?
• Are there different user roles (e.g., admin, viewer, guest)?
• Any real-time updates or live interactions?

Non-Functional Requirements

These show your foresight:

• i18n / L10n support?
• Offline functionality?
• Accessibility (a11y) compliance?
• Performance expectations (load times, interactions)?
• Security considerations (XSS, CSRF)?

👉 Tip: List constraints upfront — “We’re targeting web only,” or “Mobile-first approach.” It keeps you aligned and time-efficient.

C – Components (The Core Difference)

This is the heart of RCADO — replacing “Interface” with Components, because frontend design = UI design. Instead of abstract controllers, jump straight into:

• What components exist
• What props they take
• Who owns the state
• How data flows between them

Example: “Design a Post Feed System” You might break it down like:

Then, explain:

• Which components manage state (e.g., Feed manages pagination, PostCard is presentational).
• Which components are controlled vs uncontrolled (e.g., input fields).
• How data flows (top-down, via props; bottom-up via callbacks).

👉 Interviewers love when you naturally talk about framework-specific patterns:

• Controlled vs uncontrolled inputs
• Lifting state up
• Context / store ownership
• Memoization & rerenders

This shows real-world understanding — not just theory.

A – Architecture

Now zoom out. RCADO’s architecture focuses on state management, rendering strategy, and the communication layer.

1. Rendering Strategy

Define the approach:

• • SPA vs MPA
  • CSR vs SSR vs SSG
  • Hydration / Streaming SSR if relevant

2. State Management

Clearly define where your data lives:

• • Local state (useState in React, ref in Vue)
  • Global store (Redux, Zustand, Context, Vuex, Pinia)
  • Server state (React Query, SWR)
  • Persistent state (localStorage, IndexedDB)

Example: “Feed component subscribes to global store (React Query cache). Each PostCard gets derived props. Optimistic updates applied to likes and comments.”

3. Communication

Define your API/data-fetching layer:

• • REST / GraphQL / gRPC
  • Pagination (cursor or offset)
  • Caching and retry strategies
  • Realtime (WebSocket, SSE)

4. Routing & Layouts

• Page routing structure (/feed, /profile/:id)
• Shared layout patterns

👉 Tip: Don't focus too much on complex, backend-style diagrams. While diagrams aren't mandatory, if you have time, it's highly valuable to use a simple visual to explain how your components communicate and render efficiently, focusing on:

• Component hierarchy (parent-child relationships).
• Data flow (top-down via props; bottom-up via callbacks).
• State management boundaries (which component or store owns the data).
  
  
  

D – Data (State, Ownership & Flow)

This section covers what data exists, who owns it, and how it flows. Rather than focusing on a backend schema, show frontend structures that support scalable state.

Example (Feed System):

TypeScript

Then explain the flow:

• State ownership: Feed → owns posts array (from server state).
• Derived state: PostCard → receives post as a prop and derives isAuthor locally.
• Mutation handling: onLike(postId) triggers optimistic UI update first.
• Syncing: background refetch (React Query invalidate).

This is where you highlight modern UI framework mental models: Derived vs source of truth, Optimistic UI & rollback, Local caching & merging paginated results.

O – Other (Performance, Accessibility, Security)

Rather than a long optimization dump, RCADO suggests a live subheading approach — bring up topics when relevant during the interview.

🏎 Performance

• Virtualization for long lists
• Bundle/code splitting (lazy loading)
• Memoization (React.memo, useMemo, useCallback or framework equivalents like v-memo)
• Debounce/throttle inputs
• Prefetch next-page data

♿ Accessibility

• Semantic HTML (e.g., <button>, not <div>)
• ARIA roles for dynamic/custom elements
• Keyboard navigation and focus states
• Color contrast checks

🔐 Security

• Escape all dynamic HTML (XSS prevention)
• Avoid dangerouslySetInnerHTML
• Secure tokens in memory (not localStorage)
• CSRF-aware form submissions

👉 Mention these organically — e.g., “While rendering comments dynamically, I’d sanitize input to avoid XSS.”

Why RCADO Works Better

RADIO works well for backend-leaning designs, but RCADO is frontend-first — it mirrors how modern interviews and real-world apps are built.

Putting It All Together

When asked to design a system, start with this line:

“I’ll use the RCADO framework to structure my thought process — starting with Requirements, then diving into Components, Architecture, Data, and finally Other considerations like performance and security.”

That single line immediately signals structured, senior-level thinking. RCADO = Framework-native system design thinking. It’s clean, real, and built for how frontend engineers actually work today.