Here are the best programs to find duplicates, fix bugs, or if you just want to delete custom content (CC) from your Game. I also added tutorial videos the help you learn how to use each one of them.
After you download the mod/cc, and extracted (if they are in ZIP, RAR format), it must be placed in the following folder This computer/Documents/Electronic Arts/The Sims 4/Mods.
If some of the links below don´t work, it´s probably because its creator have deleted or moved their content to another place, and there´s nothing I can do about it. In this case, just let me know (you can leave a comment below) and I will remove it from the list, or if possible replace the link, to the new one.
SIMS 4 TRAY IMPORTER (S4TI)
Excellent program to find CC, broken CC, duplicates, save sims with/without CC, save lots with/without CC, and much more.
SIMS MOD ASSISTANT
Excellent program to find duplicates.
SIMS 4 MOD MANAGER
With this program you can find CC that you don´t want anymore and delete it. You can also disable/enable mods/CC (individually, multiple files or entire folders), view their thumbnails and use special filters.
BETTER EXCEPTIONS
Finds errors, bugs, duplicates and much more. The link may change since the creator changes it every time a new update is released.
NOTE: I didn't add the Mod Conflict Detector to the list because it's a program that hasn't been updated for a long time and it often "finds errors" that aren't even errors or non-existent duplicates, which can cause you to exclude files that are important to you and that have no problem. I only use this program to locate The Sims 2 or The Sims 3 files, and for nothing else.