How to Get Request Headers in Flask: Simple Guide

In Flask, you can get request headers using request.headers, which behaves like a dictionary containing all headers sent by the client. Import request from flask and access headers inside a route function with request.headers.get('Header-Name').

Syntax

Use request.headers inside a Flask route to access HTTP headers. It acts like a dictionary where keys are header names.

• request.headers: The object holding all headers.
• request.headers.get('Header-Name'): Safely get a specific header value.
• request.headers['Header-Name']: Get a header value but raises an error if missing.

python

from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def index():
    user_agent = request.headers.get('User-Agent')
    return f"User-Agent header is: {user_agent}"

Example

This example shows a simple Flask app that reads the User-Agent header from the incoming request and returns it in the response.

python

from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def index():
    user_agent = request.headers.get('User-Agent')
    return f"Your User-Agent is: {user_agent}"

if __name__ == '__main__':
    app.run(debug=True)

Output

Your User-Agent is: Mozilla/5.0 (example user agent string)

Common Pitfalls

Common mistakes when accessing headers in Flask include:

• Using request.headers['Header-Name'] without checking if the header exists, which raises a KeyError.
• Not importing request from flask.
• Trying to access headers outside a request context (like outside a route function).

Always use request.headers.get() to avoid errors if the header is missing.

python

from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def index():
    # Wrong: may raise KeyError if header missing
    # user_agent = request.headers['User-Agent']

    # Right: safely get header or None
    user_agent = request.headers.get('User-Agent')
    return f"User-Agent: {user_agent}"

Quick Reference

Action	Code Example	Notes
Get all headers	request.headers	Returns all headers as a dictionary-like object
Get specific header safely	request.headers.get('Header-Name')	Returns header value or None if missing
Get specific header directly	request.headers['Header-Name']	Raises KeyError if header missing
Check if header exists	'Header-Name' in request.headers	Returns True or False

Key Takeaways

Use request.headers.get('Header-Name') to safely access headers without errors.

Always import request from flask before accessing headers.

Access request.headers only inside route functions or request context.

request.headers behaves like a dictionary with all HTTP headers.

Check header existence with 'Header-Name' in request.headers before direct access.