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Multi-File CSV Concatenation

Stack selected CSV records in file order, align their headers and review the row count from every input file.

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How this works

The tool runs in this browser. Your file or text is not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.

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Drop your CSV files here

or choose them from your device

One to 10 UTF-8 files, up to 20 MB each and 80 MB in total. Every file is read in your browser.

    The union keeps every distinct heading and fills an absent cell with an empty string. Exact headings refuse a file whose heading set differs from the first file.

    When selected, each row records the file it came from. The name must not clash with an existing heading.

    Used only when the source-column option is selected.

    Detection suits a well-formed file. Set the delimiter yourself when a quoted cell confuses it.

    A cell whose first visible character is = + - or @ receives an apostrophe in the download, so a spreadsheet reads it as text. The prefix changes the stored value.

    How to use Multi-File CSV Concatenation

    1. Choose the CSV files in the order to append.
    2. Select a heading policy, optional source column and formula protection.
    3. Reopen the combined CSV and check its headings, missing cells and row count.

    Example: Multi-File CSV Concatenation

    Append two files with different headings.

    You add
    one.csv: id,name 1,Ada. two.csv: id,city 2,Paris. Mode: header union; source column off.
    You get
    The output headings are id,name,city. Rows are 1,Ada, and 2,,Paris in input-file order.

    Options

    Header mode
    Strict mode requires matching headings. Header union keeps every encountered heading and fills absent cells with empty values; it does not merge records with the same key.
    Source column and formula protection
    A source column records the input filename when enabled. Spreadsheet formula protection changes cells that could be interpreted as formulas, so review it before a machine import.

    Supported inputs and limits

    File countUp to 10 CSV files
    Input size20 MiB each; 80 MiB total
    Table bounds100,000 rows; 500 columns
    Up to ten UTF-8 files, 20 MiB each and 80 MiB combined; 100,000 total rows, 500 columns and 2,000,000 cells. Blank/duplicate headers, ragged rows, invalid UTF-8 and malformed files cause named refusals. Export is all-or-nothing, so a failed file is not silently omitted. Formula-like cells receive an apostrophe by default.

    Where your input is processed

    This tool processes your input in this browser. Your text and files are not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.

    Concatenation appends rather than reconciles

    Rows are appended in chosen file order. A union of headings can combine tables with different columns but cannot decide that differently named headings mean the same thing. Map headings first when two exports use different names for the same field.

    Empty cells can have different origins

    In header-union output, an empty value may have been blank in the source or may represent a heading absent from that file. Keep a source column when that distinction matters, and retain the original exports for a more detailed reconciliation.

    Questions about Multi-File CSV Concatenation

    Is this a key-based table join?

    No. Records are stacked in file order. The header union aligns columns but does not combine records sharing an identifier.

    What if one file cannot be parsed?

    The run refuses the combined export and identifies the problem file. Correct or remove it before trying again.

    Why does a cell gain an apostrophe?

    Formula protection prefixes cells that a spreadsheet could treat as formulas. A raw export option is available when you deliberately need the original strings.

    Project manager: Tony Hines · Content updated 4 October 2026 · Report a problem

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