ConvertCSV

Browser-based CSV transform

Join CSV

Join two CSV files on a shared key column. 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

Right CSV (lookup table)

Options

Configure how this transform runs

Output Preview

Transformed CSV

Run the transform to preview CSV output here.

Join CSV

Join CSV performs inner, left, right, or full outer joins on a shared key column — similar to SQL JOIN or spreadsheet VLOOKUP across whole tables.

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 with a shared key to joined CSV format

Overlapping non-key column names from the right file gain a _right suffix.

Common use cases

  • Enriching users with departments
  • Attaching prices by SKU

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

  • The join key must exist in both CSVs.
  • 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.