Flask-CORS is a simple extension to Flask allowing you to support cross origin resource sharing (CORS) using a simple decorator.

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Install the extension with using pip, or easy_install.

$ pip install flask-cors


This extension 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.

Simple Usage

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

Using JSON with Cross Origin

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.

@app.route("/user/create", methods=['GET','POST'])
@cross_origin(headers=['Content-Type']) # Send Access-Control-Allow-Headers
def cross_origin_json_post():
  return jsonify(success=True)

Application-wide settings

Alternatively, setting your application’s CORS_ORIGINS configuration property will

app.config['CORS_ORIGINS'] = ['Foo', 'Bar']

@cross_origin() # will return CORS headers for origins 'Foo' and 'Bar'
def helloWorld():
  return "Hello, cross-origin-world!"


flask_cors.cross_origin(origins=None, methods=None, headers=None, supports_credentials=False, max_age=None, send_wildcard=True, always_send=True, automatic_options=True)

This function is the decorator which is used to wrap a Flask route with. In the simplest case, simply use the default parameters to allow all origins in what is the most permissive configuration. If this method modifies state or performs authentication which may be brute-forced, you should add some degree of protection, for example Cross Site Forgery Request protection.

  • origins (list or string) – The origin, or list of origins which are to be allowed, and injected into the returned Access-Control-Allow-Origin header
  • methods (list) – The methods to be allowed and injected as the Access-Control-Allow-Methods header returned.
  • headers (list or string) – The list of allowed headers to be injected as the Access-Control-Allow-Headers header returned.
  • supports_credentials (bool) –

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

    Note: this option cannot be used in conjuction with a ‘*’ origin
  • max_age (timedelta, integer, string or None) – The maximum time for which this CORS request maybe cached. This value is set as the Access-Control-Max-Age header.
  • send_wildcard (bool) – If True, and the origins parameter is *, a wildcard Access-Control-Allow-Origin header is sent, rather than echoing the request’s Origin header.
  • always_send (bool) – If True, CORS headers are sent even if there is no Origin in the request’s headers.
  • automatic_options (bool) – 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.