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CSV Merge & Split

Merge several CSV files into one with matched columns, an optional source-file column and duplicate removal, or split a large CSV by row count or column value into a ZIP of smaller files.

Overview

Combines several CSV files into one or breaks one large CSV into smaller files, all inside your browser. Merging lines up columns by header name, can tag each row with the file it came from and removes duplicate rows. Splitting cuts a file by row count or by the value in a column and packs the pieces into a ZIP. Your data is never uploaded.

How It Works

In Merge mode, drop two or more CSV or TSV files; each one is listed with its row and column counts and can be removed. Choose whether headers match ignoring case, whether to add a Source file column, and how duplicates are handled. A preview of the first 50 merged rows updates as you change options, and merged.csv downloads in one click. In Split mode, drop one file, choose rows per file or a column, review the list of output files, then download them singly or as a ZIP.

Step-by-Step Usage Guide

  1. Choose Merge CSVs or Split a CSV at the top of the tool.
  2. Drop the files you want to combine, or the single file you want to split.
  3. Set header matching, the source column and duplicate handling, or the split rule.
  4. Check the preview table or the list of output files.
  5. Download merged.csv, a single part, or all parts as one ZIP.

Technical Specifications & Standards

Files are parsed with Papa Parse, which detects the delimiter, so comma, semicolon and tab separated files can be mixed in one merge. The merged header is the union of every file's columns in the order they first appear; a row from a file that lacks a column gets an empty cell there. With header matching relaxed, Email and email land in one column, and with it strict they stay apart. Removing identical rows compares the data columns only, so the same record in two files counts as a duplicate even when the Source file column differs. Removing by key column keeps the first row for each key value and never collapses rows whose key is blank. Splitting by rows repeats the header in every part and zero-pads the part numbers so files sort correctly. Splitting by column value creates one file per distinct value, turning the value into a safe file name and adding a number when two values would produce the same name. Downloaded CSVs start with a UTF-8 byte order mark so Excel reads accented text correctly.

Targeted Use Cases

  • Combining monthly sales exports into one file for a yearly report.
  • Merging contact lists from two systems and dropping duplicate email addresses.
  • Splitting a large CSV into 5,000 row chunks for an importer with a limit.
  • Creating one CSV per region or customer from a single master export.
  • Tracing which original file each merged row came from with the source column.

Notes & Gotchas

  • Remove by key column when records can differ slightly but share an ID or email address.
  • Keep header matching relaxed unless two columns genuinely differ only by case.
  • Turn on the Source file column before deduplicating so you can audit which rows were kept.
  • Trim stray spaces in the column you split by, since values are trimmed before grouping.

Frequently Asked Questions

How do I merge CSV files with different columns?

Drop all the files in Merge mode. Columns are matched by header name and every column from every file is kept, with empty cells where a file had no value for it.

Can it remove duplicate rows while merging?

Yes. Remove identical rows drops exact repeats across all files, and Remove by key column keeps only the first row for each value of a column you choose, such as email.

How do I split a CSV by the value in a column?

Switch to Split a CSV, drop the file, set Split by to Column value and pick the column. You get one file per distinct value, named after the value, ready to download as a ZIP.

Does every split file keep the header row?

Yes. The header row is written at the top of every part, whether you split by row count or by column value, so each file opens on its own.

Is there a file size limit?

Each file can be up to 60 MB. Everything is processed in browser memory, so very large merges depend on the memory available on your device.

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