All information here relates to the unheadered NTSC ROM: “Super Metroid (JU) [!].smc”, which should be 3,145,728 bytes in size and have CRC
DA957F0D63D14CB441D215462904C4FA8519C613, and MD5
21f3e98df4780ee1c667b84e57d88675; if your rom has a different checksum, then it is not a clean unheadered vanilla ROM, and you should try to acquire a new one. If you do not know how to verify your ROM's checksum, try opening the ROM in snes9x or use something like QuickHash or Microsoft's Checksum Tool.
For editing Super Metroid, the de facto standard level editor is SMILE RF. Previous notable SMILE branches include SMILE 2.5, SMILE 3 (Parlor, WINE compatible) and SMILE JX. More recently, a tool called SMART has hit the scenes, offering automatic repointing and data management in addition to level editing.
A list of guides created by the community, from manuals on the tools themselves to advanced guides relating to ASM, its all here.
Manuals of the workings of all the editors and utilities available to you, detailing all their functions.
These guides cover all the basic things around editing Metroid, as well as serving as a good starting point for learning how to get into Metroid hacking!
These guides assume you have a good basic knowledge about editing Super Metroid already, you should probably be comfortable with using SMILE by now and be moving onto using tools like a hex editor.
These guides could be pretty complex, you should probably be comfortable with assembly by now.
This segment is reserved for technical information on Super Metroid, to be used as reference material for hackers, or for the curious wanting to know what makes Samus tick, or possibly you are interested in making a fan game and want to know how Super Metroid does things!