Perfect Spawn Mod is definitely a mod designed for map makers / server owners. It allows them to not only set the exact spawn point of a world but also specify the start dimension.
To use this mod you place a file called PerfectSpawn.json in the main minecraft / server dictionary or (in a singleplayer environment) in the main dictionary of a save. The file has to have the following format:
If you create a file you always have to specify spawnX,spawnY,spawnZ and spawnDimension. exactSpawn, spawnProtection and forceBed are optional and default to true.
A PerfectSpawn.json in a world dictionary overrides the one in the main dictionary.