CSV Merger

What this tool does

CSV Merger combines multiple uploaded CSV files into one, in two modes: stacking rows together when every file shares the same columns, or joining files side by side like a spreadsheet VLOOKUP by matching a key column between them, with a CSV download of the merged result.

Combining several CSV files, monthly exports that should become one dataset, or separate files with related data that need joining on a shared ID, is a common but tedious manual task without the right tool.

This tool handles both common merge patterns: stacking rows together when files share the same column structure, or joining files side by side by matching a key column between them, the CSV equivalent of a spreadsheet VLOOKUP.

How to use CSV Merger

1. Upload two or more CSV files.
2. Choose Stack rows (same columns) or Join on a key column.
3. For join mode, pick the matching key column in the first file and in the other files.
4. Review the merged result and download it as CSV.

Tips for better results

• Stack mode assumes every file shares the exact same column structure as the first file uploaded, a warning appears if column counts don’t match, check carefully since mismatched columns can misalign data.
• Join mode performs a left join, every row from the first file is kept, with matching columns from later files added alongside; rows with no match in a later file get blank cells for that file’s columns rather than being dropped.
• The key column doesn’t need the same name across files, just matching values, select the correct column independently for the first file and for subsequent files.
• Upload files in the order you want them merged, for join mode specifically, the first uploaded file is treated as the "base" that others are joined onto.

Common use cases

• Combining several monthly or periodic CSV exports that share the same column structure into one file.
• Joining a list of records with a separate file of related details using a shared ID column.
• Merging data from two different exports into a single combined dataset for analysis.
• Consolidating multiple spreadsheet exports without manually copy-pasting rows between them.

Common mistakes to avoid

• Using stack mode on files with different column structures, which can misalign data under the wrong headers since stacking assumes identical columns across all files; check for the column-mismatch warning before trusting the result.
• Using join mode without a genuinely matching key column between files, a key column with inconsistent formatting (extra spaces, different capitalisation) between files will fail to match rows that should actually correspond.
• Expecting join mode to drop unmatched rows, it keeps every row from the first file and simply leaves blank cells where no match was found in a later file, rather than dropping that row entirely.