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

An API gateway is a single entry point for many clients into your backend system.

Main purpose

• Route requests to the right service
• Handle cross-cutting concerns centrally, such as:
  • authentication/authorization
  • rate limiting
  • logging/monitoring
  • request/response transformation
  • load balancing

Typical shape

• One gateway serves many client types:
  • web app
  • mobile app
  • external partners
  • internal tools

Focus

• Infrastructure and platform concerns
• Often tries to be generic and reusable

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Backend for Frontend (BFF)

A BFF is a backend tailored to a specific client or UI.

Main purpose

• Shape data and endpoints exactly for one frontend
• Reduce the number of calls the frontend needs to make
• Aggregate data from multiple backend services into one response
• Hide backend complexity from the UI

Typical shape

• One BFF per frontend:
  • web BFF
  • mobile BFF
  • admin dashboard BFF

Focus

• Client-specific experience and performance
• Encodes UI needs and view models

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Key difference

• API gateway = shared entry point for many clients, mostly generic concerns
• BFF = dedicated backend for one client, optimized for that frontend’s needs

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Example

Suppose a mobile app needs:

• user profile
• recent orders
• loyalty points

With an API gateway

The gateway might route /users, /orders, /loyalty to separate services, but the mobile app may still need multiple calls.

With a BFF

The mobile BFF could expose:

• GET /home and return all the needed data in one response, already shaped for the app.

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Can they be combined?

Yes. Common pattern:

• API gateway at the edge for shared concerns
• BFF behind it for each frontend

Example flow: Client → API Gateway → BFF → backend services

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Rule of thumb

Use an API gateway when you want:

• centralized routing and policy enforcement
• a standard edge layer for multiple consumers

Use a BFF when you want:

• frontend-specific APIs
• fewer round trips
• response shapes tailored to a particular UI

If you want, I can also give you a diagram or a real-world microservices example.