Frontend vs Backend: Engineering for Vibe Coders
Many vibe-coded prototypes blur the line between frontend and backend logic. UI code calls databases directly. API keys live in the browser. Business rules are hidden in client-side scripts. This often works at first, but it quickly creates security, scalability, and maintainability problems.
Understanding the difference between frontend and backend responsibilities helps you make better decisions before writing code. You do not need to be a full-stack expert. You just need to know what belongs where and why.
1. What frontend and backend really are
The frontend is everything that runs in the user’s environment. This is typically a browser or mobile app. It handles:
- Display and layout
- User interactions
- Input validation for usability
- Calling backend APIs
The backend runs on servers you control. It handles:
- Business logic and rules
- Data access and storage
- Authentication and authorization
- Integration with external services
- AI or model execution
The key difference is trust. You control the backend. You do not control the frontend.
🟢 Pre-prototype habit:
Before coding, list what must be trusted and what must not. Anything that must be protected belongs on the backend.
2. Why this distinction matters for vibe coders
Vibe coding often optimizes for speed, but mixing frontend and backend logic leads to:
- Exposed secrets and API keys
- Bypassed business rules
- Hard-to-debug behavior
- Security vulnerabilities
Keeping responsibilities clear makes prototypes safer and easier to evolve.
🟢 Pre-prototype habit:
Ask yourself: “If a user modified this code in their browser, what could go wrong?” Move that logic to the backend.
3. What logic belongs on the frontend
Frontend code should focus on:
- Displaying data
- Collecting user input
- Managing UI state
- Basic validation for user experience
- Calling backend endpoints
Frontend validation improves usability, but it is never a security control.
🟢 Pre-prototype habit:
Decide which validations are for user experience only. Plan to re-check everything important on the backend.
4. What logic belongs on the backend
Backend code is responsible for:
- Enforcing business rules
- Validating and sanitizing inputs
- Protecting secrets and credentials
- Managing data persistence
- Performing AI inference and orchestration
Anything that affects data integrity or security should live here.
🟢 Pre-prototype habit:
List your critical operations and ensure they are only possible through backend-controlled code paths.
5. Frontend and backend communication
Frontend and backend communicate through APIs. Clear boundaries matter:
- Explicit request and response formats
- Validation on both sides
- Clear error handling
- No assumptions about client behavior
This separation makes it easier to swap UIs or scale backends later.
🟢 Pre-prototype habit:
Define your API endpoints and data shapes before building the UI. Treat the API as a contract.
6. AI-specific considerations
AI features often blur boundaries:
- Prompts and inference should run on the backend
- Model keys must never be exposed to the frontend
- Output validation should happen server-side
- Rate limiting and cost controls belong in the backend
Frontend code should only request results, not control models directly.
🟢 Pre-prototype habit:
Write down where AI models run and how the frontend interacts with them before writing any prompt code.
7. Quick pre-prototype checklist
| Checklist Item | Why It Matters |
|---|---|
| Separate trusted and untrusted code | Improves security |
| Keep secrets in the backend | Prevents leaks |
| Validate inputs server-side | Protects data |
| Define API contracts early | Reduces rework |
| Keep AI logic server-side | Controls cost and risk |
Closing note
Frontend vs backend is not about technology stacks. It is about responsibility and trust. Even small prototypes benefit from clear separation.
🟢 Pre-prototype habit:
Before writing code, decide what runs in the user’s environment and what runs on your servers. That one decision prevents an entire class of problems later.
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