Merge CSV, Excel and JSON Files Online — Free

Data Mix Box lets you combine multiple spreadsheets in your browser. Drag in CSV, Excel, TSV, or JSON files. Auto-map columns across files. Remove duplicates, trim whitespace, format phone numbers, and clean your data. Export as CSV, XLSX, or JSON. No signup required. Your data never leaves your device.

How it works

1. Drop your files — drag in CSV, Excel, TSV, or JSON. Mix file types freely.
2. Map your columns — smart matching auto-links columns across files.
3. Clean your data — remove duplicates, trim whitespace, find and replace.
4. Export clean data — download as CSV, XLSX, or JSON.

Pricing

Starter is free forever: up to 3 files per merge, 10,000 rows per file, CSV export, smart column auto-mapping, exact duplicate removal.

Pro adds: up to 10 files per merge, 50,000 rows per file, XLSX and JSON export, fuzzy duplicate detection, find and replace, phone number formatting.

Frequently Asked Questions

Is my data stored anywhere?

No. All processing happens entirely in your browser. Your files are never uploaded to any server.

What file types are supported?

Import: CSV, TSV, Excel (.xlsx, .xls), and flat JSON. Export: CSV (free), XLSX and JSON (Pro).

Can I cancel Pro anytime?

Yes. Cancel anytime. You keep access until the end of your billing period.

How many rows can I process?

Starter: up to 10,000 rows per file. Pro: up to 50,000 rows per file.

Do I need to create an account?

No — you can use the free tier without an account for up to 3 downloads.