A file is listed as 'no header row found'
Its first 15 rows have no row of column names. Add a header row and run again.
Two columns that mean the same thing stay apart
Their names differ by more than case or punctuation. Rename one, or use a column map in Pro.
Numbers lost their leading zeros
They were stored as numbers in Excel. Format the column as text in the source file.
Claude does not use the skill
Check it is switched on in Settings → Capabilities → Skills, then name it in your message.
The script says a column is missing
Rename your header to one of the names in README, or say the mapping in your message.
Code execution is off
Skills with scripts need code execution enabled in Claude.ai settings.
FAQ
Which files work? CSV, TSV, semicolon-separated text and .xlsx. Old .xls files need saving as .xlsx first.
What does it drop? Blank rows, total and subtotal rows, repeated header rows and exact duplicate rows. Each is counted in report.md, and duplicates are listed in duplicates.csv.
Does it upload my files? No. Everything runs in your Claude session or on your computer.
Which row wins with --key? The later one, in the order the files are given (folders are read in name order). The replaced row is listed in duplicates.csv.