There are a few kinds of EarthBound ROMs out there. Select an EarthBound ROM on your device. The tool will analyse it to see if it's recognised. This is useful for identifying that you've got a clean ROM. If the ROM is recognised but nonstandard, it can be fixed.
While most EB ROMs floating around are already clean, some will have minor differences (that don't impact the game at all, just the file). Additionally, several legacy hacking tools will expand the ROM in a strange way or expect a copier header. Modern hacking tools usually expect a 24 megabit headerless ROM.
The copier header is a 512-byte block preceding the ROM data that used to be added by devices that dumped SNES cartridges, such as the Super Magicom. It's normally used to store information about the copier device, but when artifically adding a header, it's common to just fill it with zeroes. Emulators are smart enough to recognise when a copier header is present, but tools that edit the ROM expect things to be in very specific locations. Also, so do patches. So a clean ROM is vital for hacking.
The ROM can also be expanded to 32 megabits or 48 megabits by hacking tools in order to fit more stuff. CoilSnake does this the proper way, copying data for ExHiROM correctly and filling blank space with zeroes. JHack (aka PK Hack) does it a weird way, filling a portion of the blank space with a repeating pattern of zeroes and twos.
Here's a table of the ROMs that this tool recognises and their information. The 24-megabit headerless ROM is the clean one.
If you have a valid EB ROM that isn't in this table, contact me so I can investigate and add it to this tool.