Disclaimer: Although I have made changes to improve grammar and formatting, I didn't write this guide. It has been copied from Cowering's Good Utils Guide. Thanks to the author for creating this guide.
Good Codes
ROM files which have been named with the Good Tools naming convention have letters and numbers in their names, within brackets. These letters and numbers disclose various things about the ROM; which country the game is from, how original the ROM dump is, how accurate the dump is, what year the ROM is from, sometimes the size of the ROM, sometimes the CRC of the ROM and a few other things too. Here is a complete description...
Standard Codes
These codes tell you about the status of the ROM. Generally, the ideal ROM would be one with a [!] symbol, as such a ROM has been 100% verified against the original game. However, you may see other symbols, such as [a1] or [o3]... what these mean is that the ROM is the first known 'alternate ROM', or third known 'overdump ROM'. These extra codes are used a lot in ROM sets. Here is what they mean:
[!] Verified Good Dump
[a] Alternate to the original dump often done by another dumping group.
[o] Overdump of a ROM which has too much space allocated for it making it too big.
[p] Pirate ROM released without consent, or stolen from the original dumping group.
[b] Bad Dump of a ROM, which probably doesn't work correctly.
[f] Fixed to run better on emulators or bug fixed.
[h] Hack of a ROM that has possibly an intro added or graphics changed.
[t] Trained ROM that has a small bit of code that lets you cheat in the game.
[T] Translation of a ROM from one language to another.
(-) Unknown Year
(M#) Multilanguage (# of Languages)
(###) Checksum
(??k) ROM Size
ZZZ_ Unclassified
(Unl) Unlicensed
(-) Unknown Year
[a] Alternate to the original dump often done by another dumping group.
[o] Overdump of a ROM which has too much space allocated for it making it too big.
[p] Pirate ROM released without consent, or stolen from the original dumping group.
[b] Bad Dump of a ROM, which probably doesn't work correctly.
[f] Fixed to run better on emulators or bug fixed.
[h] Hack of a ROM that has possibly an intro added or graphics changed.
[t] Trained ROM that has a small bit of code that lets you cheat in the game.
[T] Translation of a ROM from one language to another.
(-) Unknown Year
(M#) Multilanguage (# of Languages)
(###) Checksum
(??k) ROM Size
ZZZ_ Unclassified
(Unl) Unlicensed
(-) Unknown Year
Country Codes
The codes below are to inform you of the game's country of origin. In most cases it will affect the language of the game, however, this is not always so. Public domain ROMs are home made games created by programmers and not released by software companies.
(1) Japan & Korea
(4) USA & Brazil NTSC
(A) Australia
(B) non USA (GoodGen Only)
(C) China
(E) Europe
(F) France
(F) World (GoodGen Only)
(FC) French Canadian
(FN) Finland
(G) Germany
(GR) Greece
(H) Holland
(HK) Hong Kong
(I) Italy
(J) Japan
(K) Korea
(NL) Netherlands
(PD) Public Domain
(S) Spain
(SW) Sweden
(U) USA
(UK) England
(Unk) Unknown Country
(Unl) Unlicensed
(4) USA & Brazil NTSC
(A) Australia
(B) non USA (GoodGen Only)
(C) China
(E) Europe
(F) France
(F) World (GoodGen Only)
(FC) French Canadian
(FN) Finland
(G) Germany
(GR) Greece
(H) Holland
(HK) Hong Kong
(I) Italy
(J) Japan
(K) Korea
(NL) Netherlands
(PD) Public Domain
(S) Spain
(SW) Sweden
(U) USA
(UK) England
(Unk) Unknown Country
(Unl) Unlicensed
If a particular ROM was released multiple countries, the character codes are combined to create something like (JU), which in this case signifies a Japanese/U.S. release.
Special Codes
These special codes only affect the ROMs of specific console systems.
Game Boy
[C] Game Boy Colour Version
[S] Super Game Boy Enhanced Version
[BF] Fixed to work on programmable Game Boy cartridges released by a company called Bung
Super Nintendo
(BS) Broadcast Satellaview game ROMs.
(ST) Sufami Turbo interface compatible ROMs.
(NP) Nintendo Power subscriber only games.
Atari
(PAL) Euro Version
Genesis
(1) Japan & Korean Game
(4) USA & Brazil Only Game
(5) NTSC Only Game
(8) PAL Only Game
(B) Runs on any non USA Genesis
[c] Faulty checksum routine
[x] Bad Checksum
[R-] Countries for use in.
Thomson MO5
(Y) Year unknown
Coleco
(Adam) ADAM computer version
Nintendo
(PC10) PlayChoice 10 arcade system ROM (Mame supports these)
(VS) Versus system arcade ROM (Mame supports these)
NeoGeo Pocket
[M] Mono Only
[C] Game Boy Colour Version
[S] Super Game Boy Enhanced Version
[BF] Fixed to work on programmable Game Boy cartridges released by a company called Bung
Super Nintendo
(BS) Broadcast Satellaview game ROMs.
(ST) Sufami Turbo interface compatible ROMs.
(NP) Nintendo Power subscriber only games.
Atari
(PAL) Euro Version
Genesis
(1) Japan & Korean Game
(4) USA & Brazil Only Game
(5) NTSC Only Game
(8) PAL Only Game
(B) Runs on any non USA Genesis
[c] Faulty checksum routine
[x] Bad Checksum
[R-] Countries for use in.
Thomson MO5
(Y) Year unknown
Coleco
(Adam) ADAM computer version
Nintendo
(PC10) PlayChoice 10 arcade system ROM (Mame supports these)
(VS) Versus system arcade ROM (Mame supports these)
NeoGeo Pocket
[M] Mono Only
Example: If you see a ROM named Donkey Kong Country (U) (V1.0) [!].smc, you can deduce that it's for the U.S. (U), and is an accurate ROM dump [!].
Note: The version/revision indicator (V1.0) was not mentioned in this guide.