This allows you to rename the first row of a CSV file. This is helpful if you have a large CSV file that you can't easily open, and you just need to rename the column headers to remap data. This reads the first row, and creates a form for renaming the file headers. Optionally, you can choose to add a new column. This will add a static value to all rows in that new column. This is useful if you need to add a List ID or Event Name to all lines.
After clicking "Change Headers", you need to choose where to save the newly created file. It can handle extremely large files.
This entirely happens in your browser with JavaScript - nothing is uploaded to any remote servers. Please see the source code for yourself. Feel free to run locally and modify as needed.