CrcCheckCopy - verify large data copies by the CRC of each file

CrcCheckCopy is a command line utility that lets you compare the files of different folders. It generates a CRC32 for each file and stores it in one checksum file. This small file can then be used to either check/compare another folder hierarchy or be used as an integrity check of the same folder hierarchy. The files are compared in binary mode.

The checksum file enables you to compare folders on two remote computers without needing to transfer the whole folder structure over the internet. Other file/folder comparing utilities need concurrent access to both folder hierarchies and need to read all the files (in most cases they contain some gigabytes spread in multiple files).

CrcCheckCopy is a console application (command line tool) that runs on Windows and Apple MacOS.

You can use the comments section below for any other feature requests and suggestions related to disk/folder/file comparison tasks.

Who is it for?

IT administrators, who must do reliable file copies of large volumes of data.

IT administrators can use CrcCheckCopy to ensure (with a proof) reliable data copies to their managed servers in their data centers.

Professionals in the DVD/CD authoring, mastering or mass-production industry

CrcCheckCopy was originally created for professionals in the multimedia sector. These included DVD/CD manufacturing factories, DVD/CD software authors, DVD/CD preprocessing, mastering studios.

CrcCheckCopy allows you to take a checksum file containing the CRC of each file on an incoming disk and when the processing of any files is completed, to verify the produced final disk. The utility can show which files have (expected) differences. This is something that cannot be done if you create a single CRC for the whole disk. 

Power users who want to ensure the reliability of their data copies. 

Not all copies are 100% good. This might sound funny in the era where using the computer and making copies is so easy for anyone. But here are just a few examples of what can go wrong during a copy without the user noticing it:

  • Some files do not get copied because of the limitation of the maximum directory length. The message shown by Windows will not explain to you which files were affected.
  • USB flash disks worn-out while being used. Some of their files might become "corrupted" (this is not a moral term but a computer term meaning that the files were altered by defects of the medium).
  • Copying to different files systems might alter the filename characters, e.g. Chinese or eastern European characters get converted to something that is compatible with the destination file system. These files might then become unreadable by other computers. You will most probably not see a warning about this during your file copy operation. It is a silent error.
  • Accidental user mistakes, e.g. you accidentally drag and drop some files in a different folder (the accidental file move operation can every easily go unnoticed).

CrcCheckCopy can generate signatures (CRC32 checksums) of all the source files, and compare them with the destination copy, alerting you for any differences found.

You can even store the CheckCopy utility and the checksum file to the destination disk or folder so that the recipient of the copy can verify them at any time. 

People who want to archive data files and be sure that nothing has altered them, like in the case of long-time preservation. 
Storing the checksum stamps file (and the CrcCheckCopy utility itself) together with the archived files will give you the ability to verify the integrity of your data at any time in the future. Just run the utility in verification mode, using the existing checksum stamps file.

How are you using our file comparison and crc verification utility? Use the comments below to send us your use cases. You can help us fine-tune the software and/or add new uses for it.

Pricing and License agreement

The current version is completely free.

License agreement.

How to compare the files between a source and a destination folder/disk/CD/DVD

  1. To scan all files in a folder, e.g. "c:\my-source-folder", type

    On Windows
    CrcCheckCopy /scan c:\my-source-folder
    On MacOS
    ./CrcCheckCopy /scan /my-source-folder

    The utility will read all files and store their CRCs in a file named "CRCstamps.txt", in the current directory.

    You can open this file to observe its contents.

  2. To verify and compare another folder, e.g. "c:\my-destination-folder", type

    On Windows
    CheckCopy /verify c:\my-destination-folder
    On MacOS
    ./CheckCopy /verify /my-destination-folder

    The utility will open the file "CRCstamps.txt" from the current directory, and verify that the files inside "c:\my-destination-folder" have the same CRCs.

    A new text file "CrcCheckCopy-verification-report.txt" will be created in the current directory, listing any errors found.

Filesystem permissions needed

The utility needs to create in the current directory a "CRCstamps.txt" file during the scanning/CRC generation phase and a report file during the file comparison phase.
Therefore, the user account that executes the program must have read+write permissions to the current directory (also called working directory).

For the folders that need to be scanned or compared, the user account that executes the program must have read permissions.

Software identity card
Software name: 
CrcCheckCopy - Folder comparison using CRC32 checksums.
Verify by CRC that your file/folder copies are identical.
StarMessage software
Disk/File utilities
File/folder/directory comparison utilities
Operating system: 
Microsoft Windows
Apple macOS
Average: 5 (7 votes)
  • Compare multiple destination disks in half the time.
    If you are doing muptiple copies, CrcCheckCopy can verify them in half the time. The scanning of the source disk is done only once, while the verification can be done as many times you want, using the same checksum file. No need to read again the source files.
  • The verification will skip the CRC checksum calculation if the sizes are different. This will speed up the verification process and reduce disk activity.
  • No network traffic if the files reside on different servers. Can work also without network connectivity.
  • Compare folder hierarchies or whole disks in remote locations (not on the same local network).
    You only need to send the checksum file from the computer holding the source files, to the computer where the destination files or disks are.
    E.g. a software manufacturer can send the checksum file to the DVD factory to verify that the final DVDs are verbatim copies of the original while having the option to accept differences in some "last minute" files.
  • Store the checksum file as produced by CrcCheckCopy on every important data copy or backup you do. This will allow you (or others) to check the integrity of the files at any time in the future.
  • Alternative to md5 compare function of rsync.
  • Portable executable: no installation is needed.
    No administrator account needed (because there is no installation).
  • Small size (Less than 0.5 Mb).
    Can be transferred easily and quickly via remote desktop connections.

Version history

See the version history on GitHub.

Get notifications for new version releases.

"Watch" or "Fork" our GitHub page to receive notifications for every new release.

Privacy and personal data when using this utility

You can download and use our CrcCheckCopy utility software without any kind of registration with us. Therefore your personal data are not known to us.

CrcCheckCopy uses optional telemetry functionality. With the telemetry data we can:

  • get statistics on the usage of the program so we know if it is useful and we should continue to improve and support it,
  • fix problems and crashes, and
  • improve the features of the program.

So, please enable the telemetry when asked during the first run. Your choice will be stored in an INI file so you are not asked again at the next runs.

  • On MacOS, the ini file is at ~/Library/Preferences/CrcCheckCopy.ini.
  • On Windows, the ini file is at %appdata%\StarMessage software\CrcCheckCopy.ini

You can change your decision at any time, by running CrcCheckCopy with the parameter "/t".

The telemetry is based on our "SoftMeter" product analytics and the data collected are listed here.

Examples of data included in the telemetry Examples of data NOT included in the telemetry
  • Operating system and version
  • Screen resolution
  • OS language
  • City, country (approximate)
  • Your IP address
  • Your username
  • The filenames of the scanned files
  • The contents of the files

The telemetry sends data only when the computer is connected to the internet. If the computer is not connected to the internet the data are simply discarded.


Excellent and small software. It was perfect and bug-less for HUGE data of our engineering company. Thanks to programmer to his support and to release this new version.

After copying an old partition to a new purchased hard drive, to ensure that all data are identical and to have a report for all files, I used this software. I ran it on a 400 GB folder with about 300,000 files and many many sub-folders, some file-names was in unicode.

Used software was: CrcCheckCopy v1.31 (2018)

The PC system was: OS: windows server 32bit / CPU: intel dual core 2.6GHz (an ancient CPU in 2010's) / HDD: Western Digital Gold 2TB (purchased in 2018)

It runs in less than 3 hours on the above system to generate a CRC-32 report for this huge data.


Very good, thank you so much! :-)
I love tiny and useful command line softwares! :-D

Can I do a little suggestion? The help says the syntax is:

CrcCheckCopy {/scan path | /verify path} [options]

In truth, the correct is:
CrcCheckCopy {/scan path | /verify path} patch [options]

Forcing an error, it was clear to me:
"Error: 2nd argument must be the path of the folder to check.
Run the program without parameters to see its help."

This small detail confused me a moment ago.

Once again, many thanks! *thumbsup*

PS.: I am sending the same comment again because I forgot to give 5 stars to this jewel. ;-)


Thanks for using this file comparison utility and thank you for the remark about the syntax. The next version will have the updated syntax:

CrcCheckCopy {/scan | /verify} path [options]

would be nice if path parm (2nd) was optional. if not specified the current path would be used


not working
AppData\Roaming\StarMessage software\CrcCheckCopy.ini Error message:No such file or directory


Thanks for reporting this bug. It is fixed in v1.8.


The Windows executable is identified as malicious by several antivirus programs when analyzed in I downloaded the zipped combination of Mac/Windows versions.


Thank you for reporting this.This is a false positive. It is due to the fact that it is a small command line utility and it is not digitally signed. We have submitted the program as a false positive to these antivirus companies and we expect their engines to get updated. While their desktop engines get updated fast, it is not know how frequent are the engine updates on virustotal.

We will eventually acquire a code signing certificate in the next few weeks to remove the false positives.

In the meantime, please try v1.9.


The software works really well and I have used it check the copying of some files from an old file repository to a new one. However, on about 10 of the files I got [Warning, CRC=-1] <name of file>. The software said there were no errors but what does this warning mean?


This warning is only reported because it is peculiar to find a CRC of -1 (0xFFFFFFFF in hex) as if the CRC algorithm did not even start.

Do these file pairs have the same contents? Can you make a binary comparison of them?
On Windows: fc /b fullpathtofile1 fullpathtofile2

Other cases to check for are:
- some Microsoft ISO disk images have such a CRC
- these files are symbolic links (not actual files in the directory)
- there are file permission issues for these files
- there are strange characters in their filename or file path



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