Cache-Control header directives in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Cache-Control header in HTTP?

The Cache-Control header tells browsers and other clients how to store and reuse responses to improve speed and reduce server load.

beginner

What does the directive no-cache mean in Cache-Control?

no-cache means the client must check with the server before using a cached response to make sure it is still fresh.

intermediate

Explain the difference between no-store and no-cache directives.

no-store means do not save the response anywhere, while no-cache means save it but always check with the server before reuse.

beginner

What does the max-age directive specify?

max-age sets the maximum time in seconds that a response can be used from cache without checking the server.

beginner

How does the public directive affect caching?

public means the response can be cached by any cache, even shared ones like proxies.

Which Cache-Control directive forces the client to always validate the cached response with the server before using it?

A no-cache

B no-store

C max-age=3600

D public

no-cache requires validation before reuse.

What does max-age=0 mean in Cache-Control?

A The response can be cached forever

B The response is immediately stale and must be revalidated

C The response should not be cached at all

D The response is private

max-age=0 means the cached response is stale immediately and must be checked with the server.

Which directive prevents storing the response in any cache?

A must-revalidate

B no-cache

C private

D no-store

no-store forbids storing the response anywhere.

If a response has Cache-Control: private, who can cache it?

A Any cache including proxies

B No one can cache it

C Only the browser's private cache

D Only CDN caches

private means only the end user's browser can cache the response.

What does the must-revalidate directive enforce?

A Cached responses must be revalidated after they become stale

B Responses should never be cached

C Cached responses can be used without checking

D Responses are public

must-revalidate means once the cached response is stale, it must be checked with the server before reuse.

Describe the main Cache-Control directives and their effects on caching behavior.

Think about how each directive controls storing, reusing, or validating cached responses.

Explain how Cache-Control headers help improve web performance and user experience.

Consider what happens when browsers reuse cached data correctly.

Practice

1. What does the Cache-Control: no-store directive instruct browsers to do?

easy

A. Not to save any part of the response in cache

B. Allow caching but revalidate before use

C. Cache the response for a specified time

D. Cache the response only if it is public

Solution

1. Step 1: Understand the meaning of no-store

   The no-store directive means the browser must not save any part of the response in cache.

2. Step 2: Compare with other directives

   Unlike no-cache which allows caching but requires revalidation, no-store forbids storing at all.

3. Final Answer:

   Not to save any part of the response in cache -> Option A

4. Quick Check:

   no-store means no saving [OK]

Hint: No-store means do not save anything at all [OK]

Common Mistakes:

• Confusing no-store with no-cache
• Thinking no-store allows caching with revalidation
• Assuming no-store caches for a short time

2. Which of the following is the correct syntax to set a Cache-Control header that caches content for 3600 seconds?

easy

A. Cache-Control: max-age=3600

B. Cache-Control: maxage:3600

C. Cache-Control: max_age=3600

D. Cache-Control: max-age:3600

Solution

1. Step 1: Recall correct Cache-Control syntax

   The correct syntax uses a hyphen and equals sign: max-age=3600.

2. Step 2: Identify incorrect options

   Options with colon or underscore instead of equals or hyphen are invalid syntax.

3. Final Answer:

   Cache-Control: max-age=3600 -> Option A

4. Quick Check:

   Use hyphen and equals for max-age [OK]

Hint: Use hyphen and equals sign for max-age [OK]

Common Mistakes:

• Using colon instead of equals
• Replacing hyphen with underscore
• Omitting equals sign

3. Given the header Cache-Control: public, max-age=600, what will happen when a browser receives this response?

medium

A. The response will be cached privately for 10 minutes

B. The response will not be cached at all

C. The response will be cached and shared by any user for 10 minutes

D. The response will be cached but must be revalidated every time

Solution

1. Step 1: Understand the public directive

   public means the response can be cached by any cache, including shared caches.

2. Step 2: Interpret max-age=600

   This means the cached response is fresh for 600 seconds (10 minutes) without revalidation.

3. Final Answer:

   The response will be cached and shared by any user for 10 minutes -> Option C

4. Quick Check:

   public + max-age=600 means shared cache for 10 minutes [OK]

Hint: Public means shared cache; max-age sets cache time [OK]

Common Mistakes:

• Thinking public means private caching
• Confusing max-age with no-cache
• Assuming revalidation is always required

4. You see this Cache-Control header in a response: Cache-Control: no-cache, max-age=3600. What is wrong with this header?

medium

A. The syntax is invalid because directives cannot be combined

B. The no-cache directive conflicts with max-age and disables caching

C. There is no error; this header caches for 3600 seconds

D. The max-age value must be zero when no-cache is used

Solution

1. Step 1: Understand no-cache directive

   no-cache means the cache must revalidate before using the cached response.

2. Step 2: Analyze conflict with max-age=3600

   max-age=3600 says the response is fresh for 3600 seconds, but no-cache forces revalidation, effectively disabling caching without validation.

3. Final Answer:

   The no-cache directive conflicts with max-age and disables caching -> Option B

4. Quick Check:

   no-cache overrides max-age freshness [OK]

Hint: No-cache forces revalidation, ignoring max-age freshness [OK]

Common Mistakes:

• Thinking directives cannot be combined
• Assuming max-age always overrides no-cache
• Believing no-cache disables caching completely

5. You want to ensure a sensitive API response is never stored by browsers or intermediate caches. Which Cache-Control header should you use?

hard

A. Cache-Control: no-store, no-cache

B. Cache-Control: private, max-age=0

C. Cache-Control: public, max-age=0

D. Cache-Control: no-store

Solution

1. Step 1: Identify directive that prevents any storage

   no-store tells browsers and caches not to store the response anywhere.

2. Step 2: Compare with other options

   no-cache allows storing but requires revalidation; private allows browser-only caching; public allows shared caching.

3. Final Answer:

   Cache-Control: no-store -> Option D

4. Quick Check:

   no-store forbids all storage [OK]

Hint: Use no-store to block all caching and storage [OK]

Common Mistakes:

• Using no-cache instead of no-store
• Assuming private disables all caching
• Setting max-age=0 without no-store