Command that allows you to see player's inventory and ender chest

I know there are plugins that can do this already but for new players that might get griefed (someone stealing their items and logging off/putting it in their ender chest) there might be people that don't know how to install plugins on their server/world and its overall frustrating when a friend trolls you and you can't get your items back. This might help people play the game for longer because if they worked hard on something and lost it because of a griefer they might just give up and leave Minecraft