CSV to JSON Converter

CSV to JSON Converter

Convert CSV files to JSON, and back, with delimiter detection in your browser, no upload.

Drop a file here or choose a file

CSV, TSV or TXT becomes JSON; a JSON array becomes CSV. Nothing is uploaded.

Parsing

Ctrl/⌘ + Enter converts · Ctrl/⌘ + O opens a file

How it works

  1. Add your data. Drop a CSV or JSON file, or paste text. The direction switches to match the file, and the delimiter is detected for you.
  2. Check the preview. The first 50 rows appear as a table next to the output. Adjust the delimiter, header, types or output shape; problems are listed with their row numbers.
  3. Copy or download. Copy the result or save it under the input's name, for example orders.json. It is built on your device and never uploaded.

Questions, answered

Are my files uploaded anywhere?

No. CSV to JSON Converter runs entirely in your browser. Your files are read into memory on your device, processed with JavaScript, and never sent to a server. You can disconnect from the internet and it keeps working.

How does it decide which values become numbers?

Type detection looks at each column as a whole. A column only becomes numbers (or true/false) when every filled cell agrees, and values with leading zeros such as zip codes or phone numbers stay text. Excel-style decimals with a comma, like 2,40, are kept as text. Empty cells become null. Untick the option to keep every value as a string.

My file uses semicolons or tabs. Will it work?

Yes. Comma, semicolon, tab and pipe are detected automatically, and you can pick one by hand if the guess is wrong. Rows with a different number of fields are listed with their row numbers instead of being dropped silently. Files saved by older Excel versions in Windows-1252 are decoded too.

What happens to nested JSON when converting to CSV?

Nested objects are flattened into dotted column names such as customer.name, and arrays are written as JSON text in one cell. Every key found in any record becomes a column. Cells that start with =, +, - or @ are left unchanged but flagged, because spreadsheets may treat them as formulas.

Is it really free? Does it work offline?

Yes to both. It is open source under the MIT license, with no account, no row limits and no ads. After your first visit the page is cached by a service worker, so it loads without a connection; you can also install it as an app from your browser's menu. If it saves you a paid subscription, you can say thanks on Ko-fi.

Was this written by AI?

Yes. CSV to JSON Converter was generated by Claude Code from a written specification inside an automated pipeline, with a test suite that runs in a real browser. The full source is on GitHub, so you can read every line before you trust it with your files.

Built by one person, given away for free

CSV to JSON Converter is a free alternative to paid tools like ConvertCSV and CSVJSON online converters. If it earns a place in your bookmarks, a coffee keeps the updates coming.

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