PRIVATE BY DEFAULT. INSTANT BY DESIGN.

Merge & JOIN Two CSV Files

Join CSV tables using local Map lookups, without Excel formulas or uploads.

Primary Table (Left CSV)

0 characters

Lookup Table (Right CSV)

0 characters

Left Match ColumnRight Match ColumnJoin TypeCase-insensitive matchingTrim match whitespace

Lookup columns to append

Duplicate lookup keys expand all matches. Blank keys never match. Full joins retain unmatched right keys in the left match column. Preview shows at most 100 rows.

Your CSV files stay in this browser.

Before & after: CSV VLOOKUP / Join

BEFORE · INPUT

sku,name
a-1,Notebook
b-2,Pen

AFTER · OUTPUT

sku,name,sku_right,price
a-1,Notebook, A-1 ,19.99
b-2,Pen,,

How to use CSV VLOOKUP / Join

Add CSV data

Paste CSV or drop local files. Joining requires a primary table and lookup table.

Choose options

Select match columns and join rules, chunk limits or source encoding and line endings.

Process locally

Run the task in a cancellable browser worker. Review the preview and result summary.

Download your result

Download joined or repaired UTF-8 CSV, or a ZIP of chunks with repeated headers.

Real-world workflows

Data Analysts

Use CSV VLOOKUP / Join to prepare csv vlookup / join results for repeatable reporting, exports, and data quality checks.

Software Engineers

Use CSV VLOOKUP / Join to transform source content for integration fixtures, debugging, or code review directly in the browser.

E-Commerce Managers

Use CSV VLOOKUP / Join to adapt product catalog exports and order spreadsheets for downstream inventory workflows.

Technical edge cases & frequently asked questions

Do my CSV files leave this browser?

No. Parsing, joins, repair and ZIP generation run in local browser workers. No source is uploaded.

How are duplicate and blank join keys handled?

Duplicate right keys expand to all matching rows. Blank keys do not match. Full joins copy unmatched right keys into the left match column. Matching trims whitespace and ignores case by default.

What are the practical limits?

Combined decoded sources have a 64 MiB cap; joins cap results at 1,000,000 rows and splitting caps output at 1,000 files. Device capacity varies; no under-50-ms guarantee. Quoted multiline fields are preserved and every chunk repeats its header.

Can all broken encodings be repaired?

No. Files use strict UTF-8 detection with Windows-1252 fallback; ISO-8859-1 is ambiguous and browser decoding maps it to Windows-1252. Reversible mojibake can be repaired, but lost replacement characters cannot be recovered. Review punctuation before export.

Technical specifications
Encoding	UTF-8 (text)
Processing	Local JavaScript / browser Canvas
Max recommended file size	50 MB+ may work; browser memory and tool complexity determine capacity. Start smaller.
Server retention	0 bytes — no server uploads