CSV Tools Pro

    Merge CSV Files Online

    Combine multiple CSV files into one. Files are stacked vertically with matching columns aligned. Columns with exactly matching header text are aligned; other columns are added to the output.

    Your file is processed in your browser and is not uploaded unless explicitly stated.

    Drag & drop CSV files here

    or click to browse — you can add multiple files

    What Does the CSV Merger Do?

    The CSV Merger stacks data rows in the order the files were added. It creates one header row from the distinct header text found across the files. Exact header matches share a column; otherwise a new column is added and unavailable cells are left blank.

    Merging happens in your browser. You can add or remove files before downloading one combined CSV; drag-and-drop reordering is not provided.

    How to merge CSV files

    1. Add at least two CSV files in the order they should be appended.
    2. Review the output columns and any mismatch warning.
    3. Select Merge Files, then download the result.

    When would I use this?

    • Combining monthly or quarterly data exports into a single annual file
    • Combining weekly order exports that use the same schema
    • Consolidating data collected from multiple sources before importing into a database
    • Consolidating supplier files after checking their header names
    • Combining survey results, order data, or log files collected over time into one master file

    Common Problems When Merging CSV Files

    • Monthly or quarterly exports stored in separate files are difficult to analyse together without first combining them
    • Manually copying and pasting rows between files risks introducing errors, especially with large datasets
    • Files from different sources often have slightly different column names, making merging in Excel error-prone
    • Duplicate header rows appear when concatenating files without removing the existing headers from each file
    • Large numbers of files or very large combined datasets are slow and cumbersome to handle in spreadsheet applications

    Best Ways to Merge CSV Files

    • Copy and paste in Excel — Works for very small files but becomes error-prone and slow with more than a handful of rows or files
    • Write a script — Python's pandas library or command-line utilities can merge CSV files programmatically but require setup and coding knowledge
    • Use a browser-based CSV merger — The simplest option for most users: no installation needed, add your files, configure column matching, and download the merged output in seconds

    Things to be aware of

    • The merged output must fit within available browser memory — very large combined datasets may require a script-based approach
    • Excel's 1,048,576 row limit means the merged file cannot be opened in Excel if the combined row count exceeds this
    • Column matching is name-based — columns with slightly different names across files (e.g. "Email" vs "email_address") are treated as different columns
    • Matching is case-sensitive and does not trim header spaces; "Email", "email" and "Email " are separate columns
    • Duplicate header names within one file are collapsed to one output column and the first such source column is used
    • A second file with the same name and byte size as one already added is treated as the same file and is not added again
    • CSV files do not preserve formatting, data types, or formulas — only raw values are merged
    • If source files use different encodings (e.g. UTF-8 vs Windows-1252), special characters may be garbled in the output

    Worked example

    INPUT file 1
order_id,total
1001,29.00

INPUT file 2
order_id,total,currency
1002,18.50,GBP

OUTPUT
order_id,total,currency
1001,29.00,
1002,18.50,GBP

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