Join CSV Files Online
Open several CSV, Excel 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, Excel or JSON files — each opens as its own tab (every Excel sheet too). 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 Diff JSON API Responses for Regression Testing — Catch Breaking Changes Before Users Do
Capture a baseline response before you deploy, capture it again after, and diff the two. A key-matched JSON diff surfaces renamed fields, dropped values, and type changes that a raw text diff buries in reordering noise — no server, no upload.
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.
Frequently asked questions
How do I open and compare multiple CSV files at once?+
Drop several CSV, Excel or JSON files into the workspace and each opens as its own tab (an Excel workbook opens one tab per sheet). 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.