CSV Merger

What this tool does

The CSV Merger combines several CSV files into a single CSV. You add sources by dropping files onto the upload area or by pasting CSV text into extra blocks, choose how the files should be combined, and the tool builds one merged file that you can copy or download as merged.csv. A live preview shows the first rows of the result, and a summary counts your sources, the total input rows and the output rows.

A CSV — comma-separated values — is a plain-text spreadsheet: each line is a row, and the comma-separated values on that line are the cells. Merging means taking the rows and columns from two or more such files and assembling them into one, which is something a spreadsheet can do but rarely without fiddly copy-paste.

Why and when you’d use it

Data almost never arrives in one tidy file. You might export sales month by month, pull a contact list from two different tools, or receive the same report split across regional teams. Before you can analyse or import that data, it has to become one file.

Common situations:

• Combining periodic exports. Stack January, February and March sales into one dataset for a quarterly pivot table.
• Pooling lists from several tools. Merge contacts exported from a CRM, a newsletter platform and an event sign-up sheet.
• Assembling regional reports. Each office sends its own CSV; you need the company-wide picture.
• Widening a dataset. Join a file of order totals next to a file of order statuses so every order has both in one row.

How to use it

1. Drop one or more CSV files onto the upload area. Each becomes a named source. You can also press Add a CSV to get an empty block and paste text into it. Two small samples load automatically.
2. Choose a Merge mode. Stack rows (append) puts rows on top of each other; Join side by side places columns next to each other.
3. Set the Delimiter for all sources, and toggle First row is a header if the files have no header line.
4. When stacking, decide whether to Match columns by header name. On, the tool aligns columns by their names and fills gaps with blanks; off, it aligns by position.
5. Check the preview and the summary counts, then use Copy CSV or Download .csv to save merged.csv.

Common pitfalls and tips

The most common mistake is mixing up the two modes. If your merged file has the right number of columns but far too many rows, or the reverse, you have likely picked the wrong mode — stacking makes a file taller, joining makes it wider.

Header alignment is the next thing to watch. When stacking with header matching off, two files whose columns are in a different order will interleave their data incorrectly; turn header matching on, or reorder the columns first. Empty sources are skipped automatically and noted in a message, so a stray blank block will not corrupt the result.

Beware of spreadsheet software altering values: Excel strips leading zeros from ZIP codes and SKUs and may rewrite long numbers in scientific notation, so a file that round-tripped through Excel can merge with subtly changed data. Smart quotes and odd encodings pasted from documents can also throw off parsing — paste from plain text where possible.

If you need to trim the merged file down afterwards, the CSV Column Extractor removes and reorders columns, and the CSV Row Filter keeps only rows that meet your conditions. All three tools share the same parser.

Privacy

This tool works entirely inside your browser. Every file you drop and every block you paste is read and merged by JavaScript on your own device. Nothing is uploaded, nothing is stored between visits and nothing is logged. When you close the tab, all of it is gone — so merging customer lists, payroll exports or any sensitive dataset here keeps that data private to you.