CSV Merger

How to use

1. 1Choose the merge mode at the top: Append rows stacks two CSVs vertically; Join by key lines them up by a shared column the way a VLOOKUP would.
2. 2Paste each CSV into the Left and Right boxes, or click Open CSV file to load a .csv or .tsv from your computer. Use Load sample to try the tool with example data.
3. 3Confirm whether the first row is a header. Each input delimiter can stay on Auto (the tool detects comma, tab, semicolon, or pipe) or be set manually.
4. 4For Append, pick the header policy (Match by name, Match by position, or Strict) and optionally add a source column that tags every row with its file of origin.
5. 5For Join, pick the left and right key columns, then choose the join kind (Inner, Left, Right, or Full outer). Toggle Trim and Case-sensitive to control fuzzy key matching.
6. 6Copy the merged CSV with Copy CSV or use Download to save it as .csv or .tsv. Pick the output delimiter independently of the input delimiters.

About this tool

CSV Merger combines two CSV (or TSV, semicolon, or pipe-separated) datasets directly in your browser. Two operations cover the most common reasons to merge CSV files. Append (vertical union) stacks the rows of two files that describe the same kind of record, which is what people reach for when they want to combine monthly exports, survey responses split across files, or contact lists from different sources into one larger sheet. Three header policies control how the columns line up when the files do not have identical headers: Match by header name reconciles columns by their header text and fills missing cells with empty strings, Match by position stacks them in the order they appear so files with different header names but the same shape merge cleanly, and Strict refuses to stack the data unless both headers are identical, which is useful for catching accidental schema drift between exports. An optional source column tags every output row with the file it came from so the original origin survives the merge. Join by key (horizontal merge) is the spreadsheet VLOOKUP and SQL JOIN use case: pick a key column on each side, choose the join kind, and the tool produces one wider row per matched key. Inner keeps only keys that exist on both sides, Left keeps every left row with blanks for unmatched rights, Right keeps every right row with blanks for unmatched lefts, and Full outer keeps every row from both sides. Duplicate keys produce one output row per pair, the same Cartesian behavior as a SQL join, and a clear warning surfaces when that happens so it is not a silent surprise. Key matching can trim whitespace and ignore case, which is the realistic behavior most VLOOKUP users actually want; both options are switches. The CSV parser follows RFC 4180: quoted fields, escaped double quotes (two adjacent quote characters), embedded newlines, and CRLF or LF line endings are all handled, and the parser points at the line and column of any malformed input. Auto-detect picks comma, tab, semicolon, or pipe for each input by scoring candidate delimiters on the first thirty lines, so a file exported from a German spreadsheet (semicolon-separated) and a file exported from a US spreadsheet (comma-separated) can be joined without manual configuration. The output delimiter is selectable, so the tool doubles as a delimiter converter while it merges. Useful for marketers stacking signup exports from multiple campaigns, sales teams joining a deal list to an account list by customer_id, data teams concatenating partner feeds before loading them into a warehouse, finance teams pairing a transactions export with a categories lookup, journalists combining government data tables, and anyone who would otherwise open two spreadsheet tabs and write a VLOOKUP. Both CSVs stay entirely in your browser; nothing is uploaded.

Free to use. Works in your browser. No signup, no login.