Flask JSON Content-Type decorator which validates that the Content-Type is indeed application/json. In the case of a wrong content type, then the decorator will throw an exception which can be customized.

flask json content validation decorator
pip install flask_json_content_type_validator==0.1.1


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Flask JSON Content Type Validation Decorator

This package contains a Flask routes decorator that validates that the request has a Content-Type header with 'application/json'.


Whenever you develop a Flask based API with plain vanilla flask routes that expect to get json data, then trying to access request.get_json() will return None whenever the Content-Type is not 'application/json' - which might eventually break your code. Using this decorator will help you keep your code clean and DRY.

How it works?

Create your custom exception

Below is an example of the exception you might wish to raise:

class CustomError(Exception):
    def __init__(self, message, error_code):
        self.message = message
        self.error_code = error_code

Register your custom error with a flask error handler

The decorator will throw your CustomError if the content type is not valid, in which case you can handle and return your customized response.

def custom_error_handler(custom_error):
    return flask.jsonify(dict(message=custom_error.message,
                                     error_code=custom_error.error_code)), 400

Decorate your route with the content type validator

import flask
from flask import request
from flask_json_content_type_validator import json_content_type_validator

app = flask.Flask(__name__)

    CustomError(message='Missing Content-Type header application/json',
def echo_resource():
    data = dict(**request.get_json())
    return flask.jsonify(data)