Protection Signs

Protection Signs are basically an advanced version of Lockette plugin made specially for kingdoms.
You can protect your containers with a single from others, add groups or use everyone tags.

You can protect any container such as chests, furnaces, hoppers and etc... (except ender chests since there is no reason to protect them)
All the blocks and protection mechanics can be changed in config.yml -> protection-signs

Protecting

To protect a chest, put any sign on it and type [protect], [protected], [private] or private in the first line. If the chest is successfully protected, the sign will change.
The easiest way to protect your chest is to sneak and left-click a chest with any sign in your hand. This method even works in creative and is quite quick.

Now, only you can break the chest and the sign and open the chest. Also, if you make your chest a double chest, it'll also automatically protect that without you needing to replace the sign.
You can add other players to your chest group by right-clicking on the sign. After that, a GUI with be opened and you can add players using a button and typing their name in the chat. These players can access the chest, but cannot break the sign or the chest.

Unfortunately protecting doesn't work for doors.

[Everyone]

There are two types of [Everyone] tags that you can use to protect your chest. The protection process is the same, except you have to write a different thing in the first line:

• [everyone] Everyone in your kingdom can access this chest, but cannot break it.
• [everyone*] Everyone can access this chest, whether they're in your kingdom or not, but they cannot break it.