Message editor
Using the editor you can easily create your own messages with embeds and components, e.g. buttons or select menus.
The website was developed further by the TomatenKuchen developer TomatoCake to fix some errors and add new features, which are mainly said components.
Using it with TomatenKuchen
TomatenKuchen and the Manage Bot allow you to paste JSON created by the message editor on many occurences, which simplifies the setup of embeds and co. on Discord.
You can also import messages from a channel, export to a channel and export as JSON. As the JSON is defined by Discord you can also import and export messages from other embed editors and websites and use it with TomatenKuchen.