All material related to Dungeons and Dragons 5th edition is copyright by Wizards of the Coast. This site uses information freely available from their basic rules that can be found here. This probably does not mean you can freely distribute any material derived from there - if you are Wizards of the Coast and have concerns issues with this project, contact me here.
All icons are from game-icons.net, an awesome project providing free icons for games. Parts of the CSS are copied from statblock5e, a project that tries to re-create pixel-precise monster stat blocks from the monster manual.
Click on the button below to transform the huge wall of text at the bottom into beautiful(?) spell and item cards. The cards are generated via Javascript in HTML, the card layout is such that 3x3 cards fill out an A4 page. In theory, you should be able to print the whole page (double-sided printing, flip on long edge) and get double-sided cards. However, I am no CSS expert, so the layout might be a bit off.
It should be reasonably simple to understand the JSON format I have used from the below examples, so that you can design your own cards. Just don't forget to save your JSON file externally. You can download the whole project for offline use here (note that it uses google fonts, so unless you are online, the fonts will be different).