CSV merge workflow
Merge multiple CSV files without misaligned columns
Merging files with slightly different headers can silently shift data into the wrong column. Check alignment first.
Align before combining
Confirm every source file uses the same column meaning before merging rows together.
Add each source file
Select or paste every CSV that belongs in the combined table.
Check header alignment
Confirm each column matches the same field across files.
Review the combined preview
Scan for rows that landed in the wrong column.
Download the merged CSV
Save the combined table for the next step in the workflow.
Ways to combine files
- Stack files vertically when they share the same columns
- Join on a key column when columns differ
- Keep headers from the first file or repeat them per file
Why merges go wrong
- Column order differs between source files
- One file has an extra or missing column
- Header names use different capitalization
- Some files include an extra blank row
Merge safely
- Standardize headers across files before merging
- Keep a record of which file each row came from when it matters
- Check row totals before and after merging
- Keep the original files until the merge is verified
Frequently asked questions
What happens when files have different columns?
In stack mode the merged table uses the union of columns; in join mode you pick the key column and matching rows are combined.
Are headers repeated when stacking?
That is configurable. The default keeps the header from the first file and skips the rest.
How large can the merged file be?
Merging is limited by browser memory; the recommended per-file limit is 25 MB and total output stays within a few hundred MB of working memory.
Is my data uploaded?
No. Merging happens locally in your browser.
Files are combined locally
The merge runs in the browser. Customer or financial exports are not uploaded for standard processing.
Open Merge CSV Files