This simple client sided mod allows you to see the chunk boundaries and the middle of the chunk. This can be useful when blocks need to be in the same chunk or when using a chunkloader. Simply pressing F9 will bring up the overlay.
Red lines show the corner of a chunk.
Greens lines show the boundary of a chunk.
Yellow line shows the middle of the chunk.
The key for activating the chunk overlay is F9 by default but can be changed in the controls option.
Note that this mod is only a client mod and shouldn't be installed on a server.
Inspired by the original chunk overlay in NEI by ChickenBones