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A Flask extension adding a decorator for CORS support

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A Flask extension for handling Cross Origin Resource Sharing (CORS), making cross-origin AJAX possible.


Install the extension with using pip, or easy_install.

$ pip install -U flask-cors


This extension enables CORS support either via a decorator, or a Flask extension. There are three examples shown in the examples directory, showing the major use cases. The suggested configuration is the, or the

Simple Usage

In the simplest case, initialize the Flask-Cors extension with default arguments in order to allow CORS on all routes.

app = Flask(__name__)
cors = CORS(app)

def helloWorld():
  return "Hello, cross-origin-world!"

Resource specific CORS

Alternatively, a list of resources and associated settings for CORS can be supplied, selectively enables CORS support on a set of paths on your app.

Note: this resources parameter can also be set in your application’s config.

app = Flask(__name__)
cors = CORS(app, resources={r"/api/*": {"origins": "*"}})

def list_users():
  return "user example"

Route specific CORS via decorator

This extension also exposes a simple decorator to decorate flask routes with. Simply add @cross_origin() below a call to Flask’s @app.route(..) incanation to accept the default options and allow CORS on a given route.

@cross_origin() # allow all origins all methods.
def helloWorld():
  return "Hello, cross-origin-world!"


Flask-Cors uses standard Python logging, using the module name ‘Flask-Cors’. You can read more about logging from Flask’s documentation.

import logging
# make your awesome app



Default : ‘*’

The origin, or list of origins to allow requests from. The origin(s) may be regular expressions, exact origins, or else an asterisk.



The method or list of methods which the allowed origins are allowed to access for non-simple requests.


Default : None

The header or list of headers which are safe to expose to the API of a CORS API specification


Default : None

The header or list of header field names which can be used when this resource is accessed by allowed origins.


Default : False

Allows users to make authenticated requests. If true, injects the Access-Control-Allow-Credentials header in responses.


Default : None

The maximum time for which this CORS request maybe cached. This value is set as the Access-Control-Max-Age header.


Default : True

If True, and the origins parameter is *, a wildcard Access-Control-Allow-Origin header is sent, rather than the request’s Origin header.


Default : True

If True, CORS headers are sent even if there is no Origin in the request’s headers.


Default : True

If True, CORS headers will be returned for OPTIONS requests. For use with cross domain POST requests which preflight OPTIONS requests, you will need to specifically allow the Content-Type header. ** Only applicable for use in the decorator**


Default : True

If True, the header Vary: Origin will be returned as per suggestion by the W3 implementation guidelines. Setting this header when the Access-Control-Allow-Origin is dynamically generated (e.g. when there is more than one allowed origin, and an Origin than ‘*’ is returned) informs CDNs and other caches that the CORS headers are dynamic, and cannot be re-used. If False, the Vary header will never be injected or altered.

Application-wide options

Alternatively, you can set all parameters except automatic_options in an app’s config object. Setting these at the application level effectively changes the default value for your application, while still allowing you to override it on a per-resource basis, either via the CORS Flask-Extension and regular expressions, or via the @cross_origin() decorator.

The application-wide configuration options are identical to the keyword arguments to cross_origin, creatively prefixed with CORS_









Using JSON with CORS

When using JSON cross origin, browsers will issue a pre-flight OPTIONS request for POST requests. In order for browsers to allow POST requests with a JSON content type, you must allow the Content-Type header. The simplest way to do this is to simply set the CORS_HEADERS configuration value on your application, e.g:

app.config['CORS_HEADERS'] = 'Content-Type'


For a full list of options, please see the full documentation


A simple set of tests is included in test/. To run, install nose, and simply invoke nosetests or python test to exercise the tests.


Questions, comments or improvements? Please create an issue on Github, tweet at @corydolphin or send me an email.


This Flask extension is based upon the Decorator for the HTTP Access Control written by Armin Ronacher.

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