Recently I wanted to see what would happen to my world when I convert alpha to anvil and now I would like to convert back to Alpha format for free, can someone help?
You should be able to just load the world in Alpha; converting a world leaves the original chunk files intact:
Anvil world data uses a .mca file extension, while McRegion uses .mcr. The game leaves the old McRegion files after converting a world to Anvil, despite the game never using them again.
The Wiki doesn't say if the same thing happens when converting from Alpha to Region but I would assume so, the main issue would be level.dat, which as far as I know only has a backup made of it when upgrading to Anvil (as level.dat_mcr; change the extension back to .dat to restore the original file, replacing the newer level.dat with it. Otherwise, there doesn't seem to have been any changes up to at least 1.7.10 that would make the data in the file incompatible (if you opened the world in 1.8 or later then any items in your inventory will have been converted to string IDs and this will crash the game as it tries to handle them as numbers, you'll have to use a tool like NBTExplorer to delete the inventory tag from the player entry):
Otherwise, virtually nobody ever gives backing up their vital data (even if just some Minecraft world, but anything you really don't want to lose) a second thought until it is too late, even e.g. vital business data (there are some scary statistics about how likely businesses are to fail after a major data loss due to failure to keep backups. Or maybe you were working all year on some very important school project and lost it; at the very least, always make a copy of a world before updating it to a newer version, and more ideally, at least occasionally when playing - people often report sudden random world corruption; world was fine one day, then the next day chunks are all scrambled up).
Recently I wanted to see what would happen to my world when I convert alpha to anvil and now I would like to convert back to Alpha format for free, can someone help?
You should be able to just load the world in Alpha; converting a world leaves the original chunk files intact:
The Wiki doesn't say if the same thing happens when converting from Alpha to Region but I would assume so, the main issue would be level.dat, which as far as I know only has a backup made of it when upgrading to Anvil (as level.dat_mcr; change the extension back to .dat to restore the original file, replacing the newer level.dat with it. Otherwise, there doesn't seem to have been any changes up to at least 1.7.10 that would make the data in the file incompatible (if you opened the world in 1.8 or later then any items in your inventory will have been converted to string IDs and this will crash the game as it tries to handle them as numbers, you'll have to use a tool like NBTExplorer to delete the inventory tag from the player entry):
https://minecraft.wiki/w/Region_file_format#Migration_and_level.dat
Otherwise, virtually nobody ever gives backing up their vital data (even if just some Minecraft world, but anything you really don't want to lose) a second thought until it is too late, even e.g. vital business data (there are some scary statistics about how likely businesses are to fail after a major data loss due to failure to keep backups. Or maybe you were working all year on some very important school project and lost it; at the very least, always make a copy of a world before updating it to a newer version, and more ideally, at least occasionally when playing - people often report sudden random world corruption; world was fine one day, then the next day chunks are all scrambled up).
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?