CSV to JSON Converter
Free CSV to JSON and JSON to CSV converter. Auto-detects delimiters, handles quotes and line breaks, infers types and flattens nested JSON. Private, in-browser.
- No upload — 100% private
- Instant, on your device
- Free, no sign-up
- Works offline once loaded
How it works
How to use CSV to JSON Converter
Pick CSV → JSON or JSON → CSV, then paste your data, open a .csv or .json file, or load the sample.
Leave the delimiter on Auto or choose comma, semicolon, tab or pipe.
Set whether the first row is a header and whether numbers, booleans and null should be detected.
Fix any reported problem using its line number, then copy the result or download it as a file.
Why use it
Why use our CSV to JSON Converter tool
Real RFC 4180 parser
Quoted fields, doubled quotes, commas and line breaks inside quotes, CRLF line endings and Excel's byte-order mark all work.
Delimiter auto-detect
Recognises comma, semicolon (European Excel), tab (TSV) and pipe-separated files, or set the delimiter yourself.
Smart type detection
Turns 42 into a number, TRUE into a boolean and empty cells into null — while keeping ZIP codes like 00501 as text.
Flattens nested JSON
Nested objects and arrays become dot-notation columns like address.city and tags.0, and objects with different keys share one header.
Errors with line numbers
Unclosed quotes, stray characters and invalid JSON are reported with the exact line, and rows with a different field count are flagged.
Private and offline
Files are read locally and never uploaded — safe for customer lists, exports and financial data.
FAQ
Frequently asked questions
How do I convert CSV to JSON?
Paste the CSV or open the file. With First row is header switched on, every row becomes a JSON object keyed by the column names; with it off you get an array of arrays. Then copy the JSON or download it as a .json file.
How are nested JSON objects converted to CSV?
They are flattened into dot-separated column names: {"address": {"city": "Paris"}} becomes a column called address.city, and array items get their index, like tags.0 and tags.1. Columns are the union of all keys, in the order they first appear.
My CSV uses semicolons — will it work?
Yes. Auto mode looks at the first rows and picks the delimiter that splits them into the most consistent number of columns, so semicolon files from European Excel, tab-separated TSV files and pipe-delimited files are detected automatically.
Why are some numbers kept as strings?
Values with leading zeros (like ZIP code 00501 or ID 007) and integers too large for JavaScript to store exactly stay as strings so no data is lost. Turn off type detection to keep every value as a string.
What does an unclosed quote error mean?
A field started with a double quote that never ends, so the rest of the file would be swallowed into one cell. Check the reported line for a missing closing quote, or for a quote inside a field that should have been doubled ("").
Is there a file size limit?
Files up to 50 MB can be opened. Everything is processed on your device, so very large files depend on your browser's memory — and nothing is ever uploaded.
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