Cacheable

Responses explicitly labeled

“Data within a response to a request be implicitly or explicitly labeled as cacheable or non-cacheable.” – Roy Fielding

When to use

To optimize network performance.

Why it matters

Efficiency: Reduces server load. The client (or a proxy) can reuse the last response.
Latency: No network trip for the client if cached.

Signs of Violation

Sending 200 OK for everything without Cache-Control headers.
Re-fetching static data (like list of countries) every time the user navigates.

Explanation

Problem

Fetching the same data over and over wastes bandwidth and CPU.

Solution

Use HTTP Headers: Cache-Control, ETag, Last-Modified.

Real world analogy

Grocery list. If you bought Milk yesterday and the expiration date (Cache Header) says it’s good for a week, you don’t buy Milk again today. You use the cached copy in the fridge.

Pros and Cons

Pros	Cons
Speed Lower server load	Stale data (cache invalidation is hard)

Comparison

GraphQL: Often struggles with HTTP caching compared to REST because it uses POST for queries.