What is the difference between backend for a web client and backend for a mobile application?

The differences can be in the following aspects:

• API:
  • Web: Often uses REST API, can be more verbose.
  • Mobile: May use more optimized protocols or fewer requests to reduce traffic and improve performance. Sometimes GraphQL or gRPC are used.
• Data formats:
  • Web: Usually JSON.
  • Mobile: Also often JSON, but sometimes more compact binary formats are used for traffic optimization.
• Error handling:
  • Web: Users see errors through the browser.
  • Mobile: Errors should be handled more gracefully to not disrupt user experience and provide informative messages.
• Authentication/Authorization:
  • Web: Session cookies, JWT.
  • Mobile: JWT, OAuth 2.0, tokens with limited lifetime. Offline operation considerations.
• Network optimization:
  • Web: Designed for relatively stable connections.
  • Mobile: Must consider unstable connections, low bandwidth, offline mode. Retry mechanisms, caching.
• Updates and compatibility:
  • Web: Centralized updates. Backward compatibility less critical.
  • Mobile: Multiple app versions in use. Backward compatibility API support needed.
• Push notifications:
  • Web: Via Service Workers or other mechanisms.
  • Mobile: Native platform services (FCM, APNS).
• Transaction fees (if any):
  • Web: Payment processing via web interfaces.
  • Mobile: Integration with native payment systems (Apple Pay, Google Pay).

Example of a mobile API optimized response:

// Example response for a list of products
{
  "items": [
    {
      "id": 1,
      "name": "Product A",
      "price": 100.00,
      "thumbnail_url": "..." // small image URL
    },
    // ...
  ],
  "next_page_token": "abcde12345" // for pagination
}