ConvertCSV

Browser-based CSV transform

Merge CSV

Stack two CSV files into one table with unified headers. Everything runs locally in your browser — paste CSV, set options, preview, then copy or download.

Left / primary CSV

Paste CSV or upload a file

Second CSV

Second CSV (appended below the first)

Options

Configure how this transform runs

No extra options — run the transform on your CSV input.

Output Preview

Transformed CSV

Run the transform to preview CSV output here.

Merge CSV

Merge CSV appends the second file’s rows under the first. Headers are unioned so missing columns become blank cells.

Conversion runs entirely in your browser. CSV contents are not uploaded to a server for this transform.

Key features

  • Client-side parsing and transform
  • Copy or download CSV output
  • Works with paste or file upload

About the two CSV files to merged CSV format

Column order prefers the first file’s headers, then any new columns from the second.

Common use cases

  • Combining monthly exports
  • Stacking regional sheets

How to use this tool

  1. Paste or upload CSV (and a second file when the tool needs it).
  2. Set options if shown, then click Transform.
  3. Copy or download the result.

Tips for best results

  • Align column names before merge when possible for cleaner results.
  • Preview before download and keep a copy of the original file.

Common pitfalls

Quoted commas and newlines must stay valid CSV — paste intact exports when possible.

Frequently asked questions

Is my CSV uploaded?

No. Transforms run locally in the browser tab.

For more background on data formats and conversion workflows, read our format guides or browse the converter blog for step-by-step walkthroughs linked to each tool.