Free CSV Merger Tool

The CSV Merger Tool is a free online tool that merge multiple csv files by stacking rows or joining on a common key column. It runs entirely in your browser with no installation or sign-up needed.

Vertical merge (stack rows) and horizontal join (merge by matching key column values).

Yes — add as many CSV files as needed for vertical stacking.

Yes, completely free.

Absolutely. The CSV Merger Tool processes everything client-side in your browser. No data is uploaded to or stored on any server. Your content remains private on your device at all times.

Yes, the CSV Merger Tool is fully responsive and works on smartphones and tablets. You can use it on any device with a modern web browser -- no app download required.

No account or registration is needed. Simply open the CSV Merger Tool in your browser and start using it immediately. There are no sign-up walls or usage restrictions.

Simply enter your input in the provided field, adjust any settings to your preference, and the tool will process it instantly. You can then copy the result to your clipboard or download it.

The CSV Merger Tool works in all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. For the best experience, use the latest version of your preferred browser.

A vertical stack makes your data longer by appending the rows of every file on top of one another, which is what you want when files share the same structure — like combining jan.csv, feb.csv, and mar.csv into one year-to-date sheet. A horizontal join makes your data wider instead, matching rows from two files on a shared key column and gluing the extra columns from the second file onto the first. Reach for a join when you have orders in one file and customer details in another and want them side by side. The simplest test: if your files are different time periods or batches of the same thing, stack them; if they describe the same records from different angles, join them. Pick Vertical Stack or Horizontal Join above and the tool builds the merged table automatically.

In a vertical stack the tool builds a union of every header it finds across all your files, so no columns are thrown away. When one file has a column the others lack, the cells for the rows that don't have it are simply left blank rather than knocking your data out of alignment. That means you can stack exports from slightly different tool versions or report templates without manually reconciling the columns first. The merged result keeps every column from every file, in the order they were first encountered. This is far safer than copy-pasting between spreadsheets, where mismatched headers silently shift values into the wrong columns. Upload your files above, choose Vertical Stack, and the preview shows you the combined header set instantly so you can confirm the shape before downloading.

The horizontal join is a left join, which means every row from your first file is always kept. When a key value in the first file finds a match in the second, the matching columns are attached; when there's no match, those new columns are filled with blanks instead of dropping the row. So you never silently lose records — the row count of the output equals the row count of your first file. The key column from the second file isn't duplicated in the result, and if the two files share other non-key column names, both copies will appear. You upload exactly two files for a join and pick the key column for each from a dropdown; the keys don't need identical names, only matching values. Choose Horizontal Join above to line your two files up by their shared identifier.

Key matching in a horizontal join is exact and case-sensitive, so values that look equivalent to a human won't necessarily pair. "Acme" and "acme" are treated as different keys, and so are "john@email.com " with a trailing space and "john@email.com" without one. Inconsistent exports are the usual culprit: differing capitalization, stray whitespace, or zero-padded versus unpadded IDs like "007" and "7". The fix is to clean and normalize your key column in both files before merging — make the casing consistent, trim spaces, and standardize the format. If a join leaves more blank columns than you expect, mismatched keys are almost always why. Once your keys line up exactly, paste or upload the corrected files above, pick the matching key column in each, and the join will pair every row that shares an identical value.

The live preview renders only the first 50 rows on purpose, so the table stays fast and responsive even when you merge large exports — drawing thousands of rows on screen would slow the page down for no benefit. It's a display limit, not a data limit. The full dataset is always included when you export: clicking Download saves the complete merged result as merged.csv, with no rows trimmed. The output is properly quoted too, so any values containing commas or quotation marks survive intact and open cleanly in Excel, Google Sheets, or your next script. Alongside the preview you'll see a row count and column count badge, so you can sanity-check the overall shape before committing. Merge your files above, glance at the counts to confirm everything lined up, then download the full file.