I have made a new level editor, with a start menu.

In anyone  mode press ESC to go back to the start menu

To test your level, simply press T, then u, press R if you wanna go out of test mode.

K is del.

MC/MB3 is to spawn a player

RC/MB2 is to spawn a jump block.

That's it!

Glossary: RC/MB2 right click

MC/MB3 Middle click