Tidy up a spreadsheet

Clean up a messy CSV or TSV file: trims stray spaces, puts email addresses in lower case and dates in one format, settles on one spelling of each repeated value, and removes duplicate rows. You get the tidy file plus a note of every change and of everything it could not fix, such as empty cells and dates that read two ways. It never guesses a missing value.

How it runs

Say something like "tidy up a spreadsheet" or "clean up a spreadsheet" or "clean a csv" or "tidy a csv" or "fix a messy spreadsheet" or "remove duplicate rows" in chat to start it.