Merge Multiple CSV Files
Combine two or more CSV or TSV spreadsheets into a single unified dataset. Automatically align matching headers, fill missing columns, and merge datasets 100% privately in your browser.
How to use
Upload two or more CSV or TSV files using the dropzone, or click Try example.
Inspect the loaded files list and adjust the merge strategy (Union all columns or Common columns only).
Optionally enable the source file tracking column to identify which file contributed each row.
Click Merge CSV Files to generate the combined dataset, preview the results, and download your merged .csv file.
Why Merge CSV Files in the Browser?
Data practitioners frequently deal with fragmented CSV spreadsheets: monthly sales ledgers (e.g. january.csv, february.csv), partitioned database dumps, logging batches, or marketing lists from disparate departments. Combining these files manually using spreadsheet software like Microsoft Excel is tedious, prone to accidental row loss, and often causes application freezes when handling datasets with tens of thousands of rows.
Our Merge CSV Files utility allows you to stack and concatenate multiple spreadsheets into a single master document in seconds, without uploading any files to external cloud servers.
Smart Header Alignment & Schema Handling
- Header Union (Default): When combining files that have varying column names (for example, File A has
[id, name]while File B has[id, name, department]), the tool aggregates all distinct headers into a master schema, automatically populating blank cells for records missing particular attributes. - Header Intersection: Restrict output columns strictly to the common fields present across all uploaded spreadsheets.
- Source File Audit Column: Optionally append a
_source_filecolumn to your output table, preserving provenance and tracing each record back to its originating spreadsheet. - Consistent RFC 4180 Quoting: Preserves multiline text, cells containing commas, and double quotation marks (
""), ensuring complete compatibility when loading into Python Pandas, PostgreSQL, Snowflake, or BigQuery.
Complete Browser Sandbox Privacy
Corporate financial statements, employee compensation lists, and private customer databases should never be sent across the internet to unverified third-party web services. Our CSV merger executes completely within your client-side browser runtime using HTML5 File APIs and Web Workers. Your data never leaves your device.
Frequently asked questions
What happens if the CSV files have different column headers?
By default, the merger uses 'Union' mode, which combines all unique columns from all files. If a file is missing a column found in another file, the corresponding cell is cleanly filled with a blank value.
Can I see which file each row came from?
Yes. Enable the 'Add source filename column' option, and a new column will be included in the merged output indicating the original filename for every row.
Is there a limit on how many CSV files I can merge?
Because processing happens directly in your browser's memory using Web Workers, you can merge dozens of files without upload bottlenecks or remote bandwidth caps.
Are my files uploaded to any external server?
No. All file reading, parsing, column alignment, and merging occur 100% inside your local browser sandbox. No data is transmitted over the network.
Does the tool support TSV or semicolon-delimited files?
Yes. Each file's delimiter is automatically detected, and the resulting merged dataset is formatted into standard comma-separated RFC 4180 CSV.