U wrote:

Hmmm, interesting. Which server supports automatic checksum verification and which clients do too so it would work?

You know which do support it. The ProFTPD mod_sftp and Bitvise. Also VanDyke VShell. I don't know what other SFTP client except for WinSCP does support this.

Hmmm, interesting. Which server supports automatic checksum verification and which clients do too so it would work?

I gave it a shortcut and noticed that I am able to right click the directory or file and then go to "File Custom Commands" and then verify checksum. I get error 1 for access denied when doing on a directory and an error 2 for operation not supported when trying on a file.

Yes, WinSCP has own implementation of SFTP.
Though WinSCP does not check the checksum automatically. Most servers do not support it, so it won't be much useful feature.

But there's at least an extension that will verify the files:
https://winscp.net/eng/docs/library_example_verify_file_checksum

??

Also, how do you automate checking each downloaded file? So after each file download or upload, it verifies the hashes or remote and local locations and if they don't match up, it redownloads or reuploads depending whether you're trying to upload or download.

Oh, that's awesome! I wasn't sure how it would work and happened by it by googling and found this method be the best method to verify each file transfer as 1:1 and not corrupted on the other end.

I take it that your client is based on custom code and not pigging back off PuTTY that FileZilla is doing?

WinSCP supports the check-file extension:
https://winscp.net/eng/docs/ui_properties#checksum

Here's someone asking on the filezilla forums but their client and server is based on PuTTY so won't work unless the author of PuTTY puts it in: https://forum.filezilla-project.org/viewtopic.php?t=53637

Support or no? If no, add support? If no again, why not? Only other programs I know that supports check file extension for SFTP is Bitvise. There's a nix server that can do it called ProFTP (Bitwise can do too apparently but only runs on windows) but requires you to configure it on compile, so it's not quite out of the box tick this and it works.