Join CSV Files Online
Open several CSV or JSON files as tabs, join two on a shared key column, then filter, chart, and export the combined table — all in your browser. No upload, no account, no database required.
Drop your files here
Add multiple CSV or JSON files — each opens as its own tab. Then join, filter, and chart them side by side.
Load two files to join them on a key
A workspace for many CSVs, not one.
Open every file you are working with as a tab, join the two that share a key, and explore the result — without a database, a spreadsheet, or an upload.
customer_id in customers and in orders — get stitched into one table: each order row gains its customer’s columns. It’s a SQL-style join, run entirely in your browser.| customer_id | name |
|---|---|
| C‑18 | Ada |
| customer_id | total |
|---|---|
| C‑18 | $240 |
| customer_id | name | total |
|---|---|---|
| C‑18 | Ada | $240 |
CSV guides.
Walkthroughs on joining, combining, and comparing CSV files online — from picking the right key to replacing a VLOOKUP.
How to Join Two CSV Files on a Shared Key — Without Excel or SQL
Combine two CSV files into one by matching rows on a shared key column — the browser equivalent of a VLOOKUP or a SQL join. No formulas, no database, no upload. A step-by-step guide with inner, left, right, and outer joins explained.
Clean Messy CSV Data Online — Describe the Fix, AI Writes the Rule
Excel formula wrappers like ="H4339136200", leading apostrophes, stray currency symbols, doubled quotes, rogue whitespace — the junk that shows up in exported CSVs. csvdiff.app now lets you clean any column by describing the fix in plain English; AI turns it into a reusable find/replace rule you preview before applying. All in your browser, no upload.
csvdiff.app vs Google Sheets — VLOOKUP Formulas vs Instant CSV Diff
Google Sheets is the free, no-install way most people first try to compare two CSV files, usually with VLOOKUP or IMPORTRANGE. Here's where that approach breaks down, and how a purpose-built browser CSV diff tool handles the same job in seconds.
Frequently asked questions
How do I open and compare multiple CSV files at once?+
Drop several CSV or JSON files into the workspace and each opens as its own tab. Switch between them, search and filter any dataset, and join two together on a shared key column — all without leaving the page or uploading anything.
How does joining two datasets work?+
Pick two open datasets and the column they have in common (for example customer_id or email), and the workspace builds a combined table by matching rows on that key — like a SQL join, but entirely in your browser. You can then filter, sort, and export the joined result.
Is my data uploaded anywhere?+
No. Every file is parsed, joined, filtered, and exported entirely in your browser tab and never sent to a server. That makes the workspace safe for sensitive data such as PII, financial records, or health information.
Can I mix CSV and JSON files in one workspace?+
Yes. JSON arrays are flattened into a tabular view alongside your CSVs, so you can open, join, and compare CSV and JSON datasets together and export the result in either format.
How large can the datasets be?+
Comfortably up to roughly 50,000–100,000 rows per dataset on a typical laptop. Tables are virtualised so scrolling stays smooth; joins and filters run on the main thread, so very large files may briefly pause the UI while computing.