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Free · No sign-up · Runs in your browser

Convert CSV to JSON.

Turn a spreadsheet export into clean JSON data — without a single file ever leaving your device.

Not uploaded — nobody sees it Handles quoted fields No watermark, ever No subscription or account
Your file is never uploaded — it’s processed right here in this browser tab, on your device. There’s no server involved, so we never see it, copy it or keep it.
How it works

Three steps, no waiting on a server

Altto's CSV to JSON tool works right in your browser tab, so there's no upload queue and no “processing your file” spinner tied to someone else's servers.

01

Add your CSV

Drop in a .csv file with a header row.

02

Convert

Altto parses it into structured data, locally.

03

Save your JSON

Get back a clean, ready-to-use .json file.

Why this runs in your browser, not on a server

A CSV export can hold customer records or internal data — not something you’d want sitting on a stranger’s server just to change the file format. Altto skips that step completely — there’s no server for it to go to.

  • Nothing is uploaded, everEvery file is read and converted by code that runs in this browser tab, because there’s no server on the other end. That also means we can’t see it, copy it or keep it.
  • No account, no email wallConvert as many files as you like without signing up or handing over an email address.
  • Handles real-world CSVsQuoted fields, embedded commas and escaped quotes are parsed correctly.
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files stored on our servers. There’s no server involved at all — the JSON is built once, then everything happens locally.

FAQ

Frequently asked questions

The practical details on what this tool can and can’t do. Need to go the other way? See JSON to CSV.

How does it decide the field names?
The first row of your CSV is used as the field names (keys) for every JSON object. If a column has no header, it’s named “column_1”, “column_2” and so on.
Is my file uploaded anywhere?
No — nothing is ever uploaded. The CSV is read and converted entirely inside this browser tab. There's no server involved at all, so there's nothing for Altto to see, copy or keep.
Does it handle commas and quotes inside a field?
Yes — fields wrapped in double quotes can safely contain commas, line breaks and escaped (““) quotes, following the standard CSV format most spreadsheet apps export.
What if two rows have different numbers of columns?
Each row still uses the header row’s field names — a missing value in a shorter row becomes an empty string in the JSON.
Is there a file size limit?
No hard limit, but very large CSVs (hundreds of thousands of rows) may take a moment and use noticeable browser memory, since everything happens on your device.
Do you keep a copy of my file?
No. There's no upload, so there's nothing on our side to keep. See the Privacy Policy for details.
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