This QR code API is a simple and efficient solution for generating QR codes from any URL string. The API is built with Flask, a lightweight web framework in Python, and uses the qrcode library to generate the QR codes. The API allows for sending GET requests with the URL to be converted as a parameter. The API uses an LRU cache to store frequently used QR codes, increasing the speed and efficiency of generating new codes. The API returns the QR code as a JPEG image, and includes the option to download the image as an attachment. The Content-Type header is set to 'image/jpeg' and the Content-Disposition header is set to 'attachment; filename=qr_code.jpeg' to ensure that the QR code is properly displayed and can be saved as a JPEG image. To use this QR code API, simply send a GET request to the endpoint '/qr-code' with the URL string as a parameter. The API will return the generated QR code as a JPEG image, which can be viewed or downloaded as desired.