How to Set and Inspect HTTP Request Headers with Python requests

1. Why set request headers? Request headers convey additional information to the server, such as User-Agent, Content-Type, Accept, and Authorization.

User-Agent: identifies the client type (e.g., browser or app)
Content-Type: specifies the request body format (e.g., application/json)
Accept: tells the server the response types the client expects
Authorization: used for authentication, such as a Bearer token

2. How to set request headers?

2.1 Basic settings Use the headers dictionary parameter in requests calls.

import requests

# Define request headers
headers = {
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.61 Safari/537.36',
    'Accept': 'application/json',
    'Content-Type': 'application/json'
}

# Send GET request
response = requests.get('http://example.com', headers=headers)
print(response.status_code)
print(response.text)

In this example, User-Agent, Accept, and Content-Type are set.

2.2 Setting authentication information Include an Authorization header when the API requires a token.

headers = {
    'Authorization': 'Bearer YOUR_ACCESS_TOKEN',
    'Accept': 'application/json'
}
response = requests.get('https://api.example.com/data', headers=headers)
print(response.json())

3. Viewing request and response headers

3.1 View request headers After sending a request, inspect the actual headers with response.request.headers: print(response.request.headers) 3.2 View response headers The response headers contain server information such as Content-Type and Set-Cookie: print(response.headers) 4. Common request headers and their purposes

User-Agent: simulates different browsers or clients
Content-Type: specifies the request body format (e.g., application/json)
Accept: specifies the response format the client expects
Authorization: used for authentication, usually containing a token
Cookie: used for session management

5. Precautions

Header values must be strings, bytes, or Unicode.

Header names are case‑insensitive.

The requests library adds default headers (e.g., Accept-Encoding) which can be overridden by custom headers.

6. Summary By setting request headers you can simulate various client scenarios for API testing; with requests, simply pass a dictionary to the headers argument to customize them.