What Rename Columns Does
Use this browser-based tool to rename CSV headers with an explicit old-to-new mapping. It keeps the original column order and parsed cell values, reports missing source headers and duplicate resulting names, and lets you review the result before exporting.
Create an Explicit Header Mapping
Enter one old header=new header pair per line in Old-to-new header mapping. Mappings are matched against the original header row; they do not chain from one renamed header to another.
- Blank lines and lines beginning with
#are ignored. - Lines without
=, or with an empty old header, are silently ignored. - Mapping names are trimmed before matching and renaming.
- When duplicate source headers exist, the first matching column is used.
- Repeated mappings for one source can overwrite the same target column.
Header Policies and Reports
Choose Trim policy to leave whitespace as-is or trim leading and trailing whitespace. Choose Case policy to leave case as-is, use lowercase, UPPERCASE, or Title Case. These policies affect every output header, mapped or not; they do not change cell values.
Enable Match source headers case-insensitively when the mapping and file use different capitalization. Missing mapped names appear under Missing source headers and are skipped. If final header names duplicate one another, the tool lists them under Collisions; renaming still applies.
How to Rename and Export Columns
- Paste content into Paste CSV content below, or drop/browse for a
CSV, TXTfile. Selected file text is read as UTF-8. - Enter pairs in Old-to-new header mapping.
- Choose the header policies and optional case-insensitive matching.
- As you type or change a setting, review Header preview, any reports, and Preview of result.
- Click Export CSV to download all parsed data rows.
Parsing, Export, and Reset Limitations
The file input accepts CSV, TXT, but the parser is comma-delimited and has no delimiter selector. It handles quoted fields, doubled quotes, and CR/LF line endings. It does not infer mappings or alter cell values, and it keeps column order unchanged.
The result preview shows up to 100 data rows and reports how many are shown out of the total. Export rewrites the CSV, so quoting and line endings may be normalized and the downloaded file ends with a newline; the original file bytes and formatting are not preserved.
Reset clears the mapping and automatically refreshes the result for the current CSV. Clear removes the CSV input, mapping, and result workspace.
Browser-Side Processing
The page reads selected file text with the browser FileReader API. Parsing, mapping, preview, and export run in the page script, which contains no file-upload request.
Frequently Asked Questions
Does this tool change any cell values?
No. Rename Columns only relabels the header row. Every cell value in every row passes through completely unchanged. To edit cell values instead, use Find and Replace in CSV.
Does renaming change the column order?
No. Columns stay in their original left-to-right order. Renaming only changes the label in the header row for the columns you map - it never moves, adds, or removes columns.
What happens if a mapped source header does not exist in the file?
It is listed under "Missing source headers" and skipped - it has no effect on the output. This lets you catch typos or mappings written for a different file before you export.
What happens if two headers end up with the same name?
The tool detects it and lists it under "Collisions" - whether a new name duplicates an existing untouched header or two renamed columns land on the same name. Rename still applies, but you're warned so you can adjust the mapping before relying on unique headers downstream.
What do the trim and case policies do?
Trim removes leading/trailing whitespace from every header. Case policy can convert every header to lowercase, UPPERCASE, or Title Case. Both apply to all headers in the output, including ones not touched by the mapping - they never touch cell values.
How many rows does the result preview show?
Preview of result shows up to 100 data rows and states the shown and total counts. Export CSV includes all parsed data rows.
Can matching ignore header capitalization?
Yes. Enable Match source headers case-insensitively to match mapping names without regard to capitalization. The selected trim and case policies still affect the output headers.
What happens to malformed mapping lines?
Blank lines, comment lines beginning with #, lines without =, and lines with an empty old header are ignored. The tool does not show a separate validation message for these lines.
Does the parser support tabs or another delimiter?
No. The parser uses commas and there is no delimiter selector. It does handle quoted fields, doubled quotes, and CR/LF line endings.
What does Reset do?
Reset clears the mapping and removes the result workspace. It does not restore or display an original-header result; click Rename Columns again to create a new result.