Last-Modified and If-Modified-Since in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Last-Modified HTTP header?

The Last-Modified header tells the client the date and time when the requested resource was last changed. It helps the client know if the resource has been updated since the last time it was fetched.

beginner

How does the If-Modified-Since header work in an HTTP request?

The client sends the If-Modified-Since header with a date to ask the server: "Send me the resource only if it has changed since this date." If the resource is unchanged, the server replies with a 304 Not Modified status, saving bandwidth.

beginner

What HTTP status code does the server return if the resource has NOT been modified since the date in If-Modified-Since?

The server returns 304 Not Modified. This tells the client it can use its cached copy because the resource has not changed.

intermediate

Why are Last-Modified and If-Modified-Since headers useful in REST APIs?

They reduce unnecessary data transfer by letting clients check if data changed before downloading it again. This improves performance and saves bandwidth.

intermediate

Can If-Modified-Since be used with POST requests?

No, If-Modified-Since is typically used with GET requests to check resource freshness. POST requests usually change data and do not use this header.

What does the server send if the resource has changed since the date in If-Modified-Since?

A 200 OK with the updated resource

B 500 Internal Server Error

C 404 Not Found

D 304 Not Modified

If the resource has changed, the server sends a 200 OK status with the updated resource data.

Which header does the server include to tell the client when the resource was last changed?

A If-Modified-Since

B Content-Type

C Last-Modified

D Cache-Control

The server includes the Last-Modified header with the date/time the resource was last updated.

What is the main benefit of using If-Modified-Since in client requests?

A To reduce data transfer if resource is unchanged

B To authenticate the client

C To speed up server processing

D To encrypt the data

It helps avoid downloading unchanged data, saving bandwidth and improving speed.

If the client does NOT send If-Modified-Since, what will the server do?

A Always return 304 Not Modified

B Return the full resource with 200 OK

C Return 403 Forbidden

D Return 400 Bad Request

Without If-Modified-Since, the server returns the full resource with 200 OK.

Which HTTP method is If-Modified-Since most commonly used with?

A PUT

B POST

C DELETE

D GET

If-Modified-Since is mainly used with GET requests to check if the resource has changed.

Explain how Last-Modified and If-Modified-Since headers work together to optimize data transfer in REST APIs.

Think about how the client and server communicate about resource freshness.

Describe a scenario where using If-Modified-Since would improve user experience in a web application.

Imagine a news app or social media feed updating often.