What Merge CSV Files helps you do

Merging exports by hand invites header drift and missing rows. This tool parses each file, matches columns by header name or position, and produces one previewable CSV with an optional source column. It is built for stacking monthly exports, regional files or separate survey responses without opening a spreadsheet.

Every file is parsed and merged in your browser. Nothing is uploaded to Haivix.

How it works

Each file is parsed with the selected delimiter and its header row is read. Header mode builds a union of column names and maps every row into that schema; position mode uses the first file's headers and stacks later rows by position. The merged table is rendered in a preview table and serialized back to CSV for download.

How to use Merge CSV Files

Drop two or more CSV or TSV files and reorder them if the row order matters.
Choose header matching or position stacking, and optionally add a source file column.
Merge the files, review the preview and the row count, then download the combined CSV.
Fix a header spelling and merge again if a column is unexpectedly blank.

When to use it

Combine monthly exports that share columns but not column order.
Stack regional files into one import while keeping track of the source file.
Append survey or form responses collected in separate files.
Combine exports from two systems that use slightly different header names.
Build one file for a bulk import that accepts a single upload.
Add an audit column that names the source of every row.

When not to use it

Do not merge files with different meanings for the same column name.
Do not use position mode when the columns may be in a different order.
Do not merge files that exceed the per-file size cap or the browser's memory.

Example

January and February exports both have date, region, product and revenue, but February puts region first. Header mode merges them correctly and adds a source column with january.csv or february.csv on each row, so a later pivot can still separate the months.

What you can do with Merge CSV Files

Combine two or more CSV or TSV files.
Match columns by header name or by column position.
Reorder the input files before merging.
Add a source-file column to trace each row.
Preview the merged result before downloading it.
Download the combined data as CSV.

Example: stack monthly sales exports

Drop the monthly files and check the header names in the preview. If the columns are in different orders, header mode lines them up by name rather than position.

Add a source column when you need to know which file each row came from, then reorder the files if the output row order matters.

Merge, review the row count and the blank cells, and download the CSV. A large blank column is a sign that two files use different header spellings.

What to know before you start

Header mode unions columns; a column missing from one file becomes blank for those rows.
Position mode trusts column order and ignores extra columns beyond the first file's headers.
A merge is limited by available browser memory and the 25 MB per-file cap.
Duplicate header names in one file are not supported.
Merging does not deduplicate rows.

Common mistakes

Using position mode on files whose columns are in a different order.
Ignoring a blank column that reveals a header spelling mismatch.
Forgetting that the source column is optional and then losing track of the origin.
Reordering files after reviewing the preview and merging the old order.
Assuming the merge sorts rows; it preserves the file and row order.

Troubleshooting

If a column is mostly blank, compare the header spelling in each file. Header mode treats region and Region as different unless the parser normalizes them.

If rows are shifted, position mode is active with mismatched columns. Switch to header mode.

If the merge fails on a large set, reduce the number of files per pass or split the data first.

If the delimiter looks wrong, confirm whether the source uses commas, tabs or semicolons before merging.

If the preview does not update, reorder the files again or reload the page to reset the preview state.

If two files use different date formats, header mode still merges them, but the merged column contains both formats. Normalize the dates in the source or convert them after the merge; do not assume the preview parsed them as dates. A quick sort on the column usually exposes the two shapes.

Merge CSV Files