What's the difference between an API gateway and a Backend for Frontend?

An API Gateway and a Backend for Frontend (BFF) both sit between clients and backend services, but they solve different problems.

API Gateway

A gateway is a generic entry point for many clients and many backend services.

Main purpose

• Route requests to the right service
• Handle cross-cutting concerns:
  • authentication/authorization
  • rate limiting
  • logging/metrics
  • request/response transformation
  • SSL termination
• Hide internal service topology

Characteristics

• Usually shared by multiple clients: web, mobile, partner apps, etc.
• Usually organization/platform-oriented
• Not usually tailored heavily to one specific UI
• Can be “thin” and mostly pass-through

Example

/users/123 gets routed to the User Service, /orders/456 to the Order Service.

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Backend for Frontend (BFF)

A BFF is a backend built for a specific frontend or client type.

Main purpose

• Provide exactly the data and shape a particular UI needs
• Reduce chatty calls from the frontend
• Aggregate data from multiple downstream services
• Encapsulate frontend-specific logic

Characteristics

• Usually one BFF per frontend:
  • web BFF
  • mobile BFF
  • admin dashboard BFF
• Optimized for a particular user experience
• Often does orchestration and composition
• May expose endpoints that don’t map cleanly to internal services

Example

A mobile app may want:

• user profile
• recent orders
• notifications all in one response from /home-screen

The BFF combines data from multiple services and returns a mobile-friendly payload.

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Key difference in one sentence

• API Gateway = shared infrastructure for routing and policy enforcement
• BFF = client-specific backend optimized for a particular frontend

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Comparison

Aspect	API Gateway	BFF
Audience	Multiple clients	One specific frontend/client type
Focus	Infrastructure and policies	UI-specific data and orchestration
Scope	Broad, generic	Narrow, tailored
Data shaping	Minimal to moderate	Heavy, frontend-oriented
Number of instances	Usually one per platform/edge	Often one per frontend
Typical ownership	Platform/backend team	Frontend/product team or joint

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Can they be used together?

Yes. Common setup:

Client → BFF → API Gateway → Microservices

Or sometimes:

Client → API Gateway → BFF → Microservices

Though in many architectures, the BFF is the “edge” backend and the gateway may sit behind it or be folded into it depending on the team and scale.

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Rule of thumb

• Use an API Gateway when you need shared ingress, security, routing, and operational control.
• Use a BFF when a frontend needs a custom backend tailored to its UX and data needs.

If you want, I can also give you a real-world architecture diagram or when to choose one vs the other.