A 3DS file converts to CCI using a command-line tool called ctrtool, which reads the 3DS container and rewrites it in CCI format

The 3DS and CCI formats both hold Nintendo 3DS game data, but they package it differently. A 3DS file is a decrypted, uncompressed dump of a game cartridge. A CCI file is the same game data, but encrypted and in the exact format that matches a physical cartridge. Converting between them is a technical process that requires specific software and some comfort with command-line tools.

This conversion is legal only if you own the original game cartridge and are converting your own backup. Distributing or downloading converted files is not legal, and neither is converting games you do not own.

Key Takeaways

  • You will need ctrtool (a command-line utility), a 3DS file you own, and a computer running Windows, macOS, or Linux to perform the conversion.
  • The conversion process involves opening a terminal or command prompt and running a single command that specifies your input 3DS file and output CCI filename.
  • The converted CCI file will be the same size as the original 3DS file, and the process typically takes a few seconds to a few minutes depending on file size.
  • If ctrtool does not recognize your 3DS file, the file may be corrupted, incomplete, or in a format that ctrtool does not support.

What you need before you start

read ctrtool from its official repository on GitHub. Search for "ctrtool" and look for the repository maintained by Relys or the most recently updated fork. read the version that matches your operating system: ctrtool.exe for Windows, or the compiled binary for macOS or Linux. If you read source code instead of a compiled binary, you will need to compile it yourself using a C compiler, which adds an extra step.

Gather your 3DS file and know where it is stored on your computer. Write down the exact filename and file path, or keep the file in an straightforward-to-find location like your Desktop or Documents folder. You will type this path into the command line, so accuracy matters.

Open a terminal or command prompt on your computer. On Windows, press the Windows key, type "cmd", and open Command Prompt. On macOS, open Applications > Utilities > Terminal. On Linux, open your distribution's terminal process. This is where you will type the conversion command.

The conversion command and what each part does

The basic command structure is:

ctrtool -x -t cci input_file.3ds -o output_file.cci

Break this down: ctrtool is the program name. -x tells ctrtool to extract or convert the file. -t cci specifies that you want CCI format as the output. input_file.3ds is the name of your 3DS file — replace this with the actual filename. -o output_file.cci sets the name and location of the file ctrtool will create.

If your 3DS file is on your Desktop and named "game.3ds", and you want the CCI file to also be on your Desktop and named "game.cci", the command looks like this on Windows:

ctrtool -x -t cci C:\Users\YourUsername\Desktop\game.3ds -o C:\Users\YourUsername\Desktop\game.cci

On macOS or Linux, it looks like:

ctrtool -x -t cci ~/Desktop/game.3ds -o ~/Desktop/game.cci

Replace "YourUsername" with your actual Windows username, and replace "game" with your actual filename. Type or paste the command into the terminal and press Enter. The conversion will begin when ready.

What happens during and after the conversion

While ctrtool runs, you will see text output in the terminal showing the conversion progress. The tool reads the 3DS file, processes the data, and writes the CCI file. For a standard game file (typically 1 to 4 gigabytes), this takes between 30 seconds and 5 minutes. Larger files take longer.

When the conversion finishes, the terminal will return to a blank prompt and you will see no error message. This means the conversion succeeded. Navigate to the folder where you told ctrtool to save the output file, and you will find your new CCI file. Check that the file size is the same as the original 3DS file — if the CCI file is much smaller or much larger, something went wrong.

If the terminal shows an error message like "File not found" or "Invalid input", check that you typed the filename and path correctly. If you see "Unsupported file format", the 3DS file may be corrupted or in a format ctrtool does not recognize. Try the conversion again with a fresh copy of the 3DS file if you have one.

Why you might need CCI format instead of 3DS

CCI format is useful if you are using emulation software or tools that specifically require cartridge-format files. Some backup and archival workflows also use CCI because it matches the physical cartridge structure exactly. If you are straightforward storing a backup of a game you own, 3DS format works just as well and requires no conversion.

CCI files are larger than compressed formats like CIA (another Nintendo 3DS format), so if storage space is a concern, CCI is not the most efficient choice. However, if your workflow or software requires CCI specifically, the conversion is straightforward once you have ctrtool installed.

Troubleshooting common problems

If ctrtool does not run at all, you may need to navigate to the folder where ctrtool is stored before you can use it. On Windows, open Command Prompt in the same folder as ctrtool.exe by holding Shift, right-clicking in the folder, and selecting "Open command window here". Then type the conversion command without the full path to ctrtool.

If the conversion starts but stops with an error partway through, the 3DS file may be incomplete or corrupted. Try downloading or copying the 3DS file again from your source. If the error persists, the file itself may be damaged beyond repair.

If you see a message about missing encryption keys, your version of ctrtool may be outdated or missing required key files. Check the ctrtool repository for updated versions or documentation about key files. Some versions of ctrtool require a keys.txt file in the same folder as the executable.

Frequently Asked Questions

Can I convert a CCI file back to 3DS format?

Yes, ctrtool can convert in both directions. Use the same command structure but change -t cci to -t 3ds and swap your input and output filenames. The process is identical and takes the same amount of time.

Will the converted CCI file work in emulators?

Some emulators accept CCI files, but others require 3DS or CIA format. Check the documentation for the specific emulator you are using. Most modern emulators support multiple formats, but not all.

Does the conversion change the game data or make it unplayable?

No. The conversion only changes the container format, not the actual game code or content. A CCI file created from a 3DS file contains identical game data and will play identically.

How much disk space do I need for the conversion?

You need free space equal to the size of both the original 3DS file and the new CCI file combined. If your 3DS file is 2 gigabytes, you need at least 4 gigabytes of free space on the drive where you are saving the CCI file.

What if ctrtool says "permission denied"?

On macOS or Linux, you may need to make ctrtool executable first. In the terminal, type chmod +x ctrtool and press Enter, then try the conversion command again. On Windows, check that your user account has permission to write files to the folder where you are saving the CCI file.