Request headers (Content-Type, Accept) in Rest API

Introduction

Request headers tell the server what kind of data you are sending and what kind of data you want back. This helps the server understand and respond correctly.

When sending JSON data to a server, you use Content-Type to say the data is JSON.

When you want the server to send back XML instead of JSON, you use Accept to ask for XML.

When uploading a file, you use Content-Type to tell the server the file type.

When calling an API that supports multiple formats, you use Accept to specify your preferred format.

Syntax

Rest API

Content-Type: media/type
Accept: media/type

Content-Type tells the server the format of the data you are sending.

Accept tells the server the format you want in the response.

Examples

You send JSON data and want JSON back.

Rest API

Content-Type: application/json
Accept: application/json

You send form data and want an HTML page back.

Rest API

Content-Type: application/x-www-form-urlencoded
Accept: text/html

You upload files and want JSON response.

Rest API

Content-Type: multipart/form-data
Accept: application/json

Sample Program

This Python program sends JSON data to a test server with Content-Type and Accept headers set to application/json. It prints the status code, the response content type, and the JSON data the server received.

Rest API

import requests

url = 'https://httpbin.org/post'
headers = {
    'Content-Type': 'application/json',
    'Accept': 'application/json'
}
data = {'name': 'Alice', 'age': 30}

response = requests.post(url, json=data, headers=headers)
print(response.status_code)
print(response.headers['Content-Type'])
print(response.json()['json'])

Important Notes

Always set Content-Type when sending data so the server knows how to read it.

Use Accept to tell the server what response format you prefer, but the server may not always honor it.

Headers are case-insensitive but usually written with capital letters and hyphens.

Summary

Content-Type header tells the server the format of your request data.

Accept header tells the server what response format you want.

Setting these headers helps APIs communicate clearly and avoid errors.

Practice

1. What does the Content-Type header specify in an HTTP request?

easy

A. The format of the data being sent to the server

B. The format of the data the client wants to receive

C. The server's IP address

D. The HTTP method used in the request

Solution

1. Step 1: Understand the role of Content-Type

   The Content-Type header tells the server what format the request body data is in, such as JSON or XML.

2. Step 2: Differentiate from Accept header

   The Accept header tells the server what response format the client wants, not the data sent.

3. Final Answer:

   The format of the data being sent to the server -> Option A

4. Quick Check:

   Content-Type = request data format [OK]

Hint: Content-Type = your data format sent [OK]

Common Mistakes:

• Confusing Content-Type with Accept header
• Thinking Content-Type is about response format
• Ignoring the header completely

2. Which of the following is the correct way to set the Accept header to request JSON data in an HTTP request?

easy

A. Content-Type: application/json

B. Accept: text/html

C. Accept: application/json

D. Content-Type: text/plain

Solution

1. Step 1: Identify the Accept header usage

   The Accept header tells the server what response format the client wants, such as JSON.

2. Step 2: Match the correct MIME type for JSON

   The MIME type for JSON is application/json, so the header should be Accept: application/json.

3. Final Answer:

   Accept: application/json -> Option C

4. Quick Check:

   Accept header for JSON = application/json [OK]

Hint: Accept header = desired response format [OK]

Common Mistakes:

• Using Content-Type instead of Accept for response format
• Using wrong MIME type like text/html for JSON
• Mixing up header names

3. Given this HTTP request snippet:

POST /api/data HTTP/1.1
Host: example.com
Content-Type: application/json
Accept: application/xml

{"name": "Alice"}

What format will the server expect the request body to be, and what format will it try to respond with?

medium

A. Request body XML, response JSON

B. Request body XML, response XML

C. Request body JSON, response JSON

D. Request body JSON, response XML

Solution

1. Step 1: Analyze Content-Type header

   The Content-Type is application/json, so the server expects JSON data in the request body.

2. Step 2: Analyze Accept header

   The Accept header is application/xml, so the client wants the response in XML format.

3. Final Answer:

   Request body JSON, response XML -> Option D

4. Quick Check:

   Content-Type = JSON, Accept = XML [OK]

Hint: Content-Type = sent data, Accept = wanted response [OK]

Common Mistakes:

• Mixing up Content-Type and Accept roles
• Assuming response matches request format
• Ignoring headers and guessing defaults

4. You wrote this HTTP request:

POST /submit HTTP/1.1
Host: example.com
Content-Type: application/json
Accept: application/json

name=John&age=30

Why might the server reject this request or fail to parse the data?

medium

A. Because the HTTP method POST is not allowed

B. Because the Content-Type says JSON but the body is URL-encoded form data

C. Because Accept header is incorrect for JSON

D. Because the Host header is missing

Solution

1. Step 1: Check Content-Type and body format

   The Content-Type is application/json, but the body is name=John&age=30, which is URL-encoded form data, not JSON.

2. Step 2: Understand server parsing behavior

   The server expects JSON data but receives form data, so it may reject or fail to parse the request.

3. Final Answer:

   Because the Content-Type says JSON but the body is URL-encoded form data -> Option B

4. Quick Check:

   Content-Type must match body format [OK]

Hint: Match Content-Type with actual body format [OK]

Common Mistakes:

• Ignoring mismatch between Content-Type and body
• Assuming Accept header affects request body
• Thinking Host header is missing when it is present

5. You want to send JSON data to an API and receive a JSON response. Which headers should you set correctly in your HTTP request to ensure this communication?

hard

A. Content-Type: application/json and Accept: application/json

B. Content-Type: text/plain and Accept: application/json

C. Content-Type: application/json and Accept: text/html

D. Content-Type: application/xml and Accept: application/json

Solution

1. Step 1: Set Content-Type for request data

   Since you are sending JSON data, set Content-Type: application/json so the server knows the format of the data you send.

2. Step 2: Set Accept for response format

   To receive JSON response, set Accept: application/json to tell the server you want JSON back.

3. Final Answer:

   Content-Type: application/json and Accept: application/json -> Option A

4. Quick Check:

   Both headers set to application/json for JSON exchange [OK]

Hint: Both headers must match JSON for send and receive [OK]

Common Mistakes:

• Setting Content-Type and Accept to different formats
• Using text/plain or XML when JSON is needed
• Forgetting to set Accept header