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Data

CSV to JSON Converter

Paste CSV with a header row and convert it into clean JSON in your browser. Nothing is uploaded — runs in your browser.

Runs in your browserPrivate by designCSVJSON
CSVJSON

Press ⌘ Enter to run

4 lines · 69 chars

Ready — press Run or ⌘ Enter

How this tool handles files

Processing
In your browser, on-device
Storage
Nothing stored
Output
A file you download
Your responsibility
Review before official use
  • Runs in your browser. Your file is processed on your own device and, on this site, is not uploaded to our servers.
  • Nothing is stored. Your file and its output are gone the moment you close or reload the page.
  • Review sensitive files (bank, ID, medical) and check the output before sharing it.

Every tool on FormatOS runs in your browser. Read our Privacy Policy and File Handling Policy.

Common uses

  • Prepare data for an API request
  • Convert exported spreadsheet rows to JSON
  • Inspect CSV structure in a developer-friendly format

Limitations

  • Numeric and boolean detection is best-effort
  • Very large files can hit browser memory limits

What this CSV to JSON tool produces

Paste CSV text with a header row and the tool returns a JSON array of objects, pretty-printed with two-space indentation. The first row becomes the keys; every following row becomes one object. So a header of name,category,count over three data rows produces three objects, each with name, category, and count properties in the order they appeared.

Values are carried through as text exactly as written in the cells. The tool does not coerce 128 into a number or true into a boolean for you, so a count column arrives as "128" rather than 128. If your API or schema needs typed values, plan to cast them after conversion. This keeps the output predictable and avoids guessing wrong about fields like zip codes or IDs that look numeric but should stay strings.

Once converted, you can copy the JSON to the clipboard or download it as formatos-csv-to-json.json. The output panel also reports line and character counts so you can sanity-check the size before reusing it elsewhere.

Quoting, line endings, and ragged rows

The parser follows the usual CSV quoting rules, so commas, line breaks, and quote marks inside a quoted field are handled correctly. A cell written as "Smith, John" stays as one value rather than splitting into two, and a doubled quote ("") inside quotes is read as a single literal quote character in the result.

Both Unix (LF) and Windows (CRLF) line endings are accepted, which matters when you move files between editors or operating systems. Rows that are shorter than the header simply fill the missing trailing fields with empty strings, so a malformed export will not throw away the rest of your data.

One edge case to watch: if a header cell is blank, that column is named column_1, column_2, and so on by position. Give every column a clear header before converting if you want readable, stable keys in the JSON.

Running it locally and handling large files

This is a paste-in tool that runs entirely in your browser. There is no file upload, so the CSV you paste stays on your machine rather than going over the network. A sample loads automatically the first time so you can see the shape of the output, and you can press Reset sample to return to it at any point.

Trigger a conversion with the Run button or Ctrl/Cmd+Enter from the input box. Conversion is scheduled on the next animation frame, which keeps the interface from freezing while a larger paste is processed.

Because the work happens in the page, very large inputs can hit browser memory limits and feel sluggish or fail. If you are working with a huge export, convert it in smaller chunks, or trim columns you do not need before pasting so the browser has less to hold in memory at once.

Frequently asked questions

Yes. The first row is treated as the header, and each following row becomes a JSON object whose keys are those column names.

Values that look like numbers or booleans are detected automatically and written without quotes. This is best-effort — if a column should stay text (like a ZIP code or phone number), double-check the output.

No. The conversion runs in your browser — your text or file is processed on your own device and, on this site, is not uploaded to a server, and we do not intentionally store it.

Quoted fields are parsed correctly, so a value like "Smith, John" wrapped in quotes stays a single field. Unquoted stray commas can still split a row, so quote fields that contain commas.

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Tool last reviewed: June 30, 2026 · Report a problem