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Spreadsheet Merge and Split - CSV and Excel

Combine several CSV or Excel files into one, matching columns by name even when the order differs, or split one file into parts by row count or by the values in a column. Up to 20 files, all processed in your browser. Nothing is uploaded.

Merging and Splitting Without Copy-Paste Mistakes

Exports rarely line up. One system puts the email address in the second column, the next puts it in the fifth and calls it E-mail. Pasting those under each other in a spreadsheet silently mixes columns. Merging by header name avoids that: columns are matched by their title, ignoring case and spaces, the headers are combined, and a column one file does not have is simply left empty for its rows. A Source column records which file each row came from, which is the first thing you need when a number looks wrong later.

Splitting goes the other way. A mailing tool accepts 1,000 contacts per import, so a file of 8,400 becomes nine parts, each with the header. A sales export needs to go to one account manager per region, so it is split on the Region column into one file per value. The parts come as a zip of CSV files or as one Excel workbook with a sheet per part, whichever the next step wants.

Excel files are read and written here without a spreadsheet library: the tool opens the .xlsx package, reads the cell values, turns date cells into readable dates and text into text, and writes plain workbooks Excel, Numbers and Google Sheets open without complaint. Formulas come through as their last calculated value; formatting and charts are not carried over. Everything runs in your browser, and the same merge and split are available to scripts and AI agents through the ToolForte REST API and MCP server for CSV text.

How Spreadsheet Merge and Split Works

  1. 01Add up to 20 files: .csv, .tsv, .txt or .xlsx. Every sheet of an Excel file is read, the first row is the header, and the delimiter of each CSV is detected.
  2. 02To merge, choose whether columns are matched by header name or kept by position, and whether a Source column with the file name is added. Download one CSV, one Excel sheet or one workbook with a sheet per input.
  3. 03To split, pick the first file and split it every N rows or on the values of a column. Every part keeps the header.
  4. 04Download the parts as a zip of CSV files or as one Excel workbook with a sheet per part. Nothing leaves your browser.

Matching by Header Name Versus by Position

Two exports of the same data rarely have the same column order. One system writes Name, Email, City; the next writes email, city, name and adds Phone. Matching by header compares names without regard to case and surrounding spaces, unions the headers in the order they were first seen, and leaves a cell empty when a file does not have that column. That is the safe default. Matching by position is for files that came from the same template and have no header names worth trusting: the first file's header is kept and every following row is appended as it is. Excel files are read cell by cell: shared strings, inline strings, booleans and numbers, with cells styled as dates turned into readable dates. Formulas arrive as their last calculated value. Output workbooks are plain, one sheet per table, without styles, and open in Excel, Numbers, LibreOffice and Google Sheets.

When to Use This Tool

Monthly exports that must become one yearly file. Contact lists from several forms that need to become one import. A large file that has to be cut into chunks of a thousand rows because an import tool has a limit. A national report that must be split per region or per account manager so each person gets only their own rows. And any time you would otherwise paste sheets under each other by hand and hope the columns line up.

Frequently Asked Questions

Are my files uploaded?→
No. Files are read, merged, split and written in your browser. The same merge and split are available to scripts and AI assistants through the ToolForte REST API and MCP server, which take CSV text as input and return CSV text.
What happens to a column that only one file has?→
With matching by header it becomes a column in the merged file, filled for the rows from that file and empty for the others. With matching by position it is dropped if the first file has fewer columns.
Does it keep Excel formatting, formulas and charts?→
No. The tool works with values. Formulas come through as their last calculated result, dates as readable dates, and the output workbook has no styles or charts.
Which delimiter does it use?→
On input, each CSV's delimiter is detected: comma, semicolon, tab or pipe. On output the browser tool writes commas; the API accepts a delimiter parameter.
How large can the files be?→
The browser tool handles files of tens of megabytes, limited by your device's memory. The API accepts up to 2 million characters per CSV and 20 files per merge, and a split may produce at most 200 parts.

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