CSV to JSON Converter Online - Fast, Secure & Private
Updated
Convert CSV to JSON online instantly. Transforming table data into structured JSON objects or arrays. 100% client-side privacy. Free online tool.
Key Features
- ✅ Outputs a JSON array of row objects
- ✅ Preserves values as strings (no accidental number/boolean coercion)
- ✅ Automatic delimiter detection (comma, semicolon, tab, pipe)
- ✅ Automatic header-row parsing
How to Use
- Paste your CSV or upload a file
- Click Convert — there are no configuration options; the first row is always treated as the header
- Click Convert to generate JSON
- Copy the resulting JSON string for use in your code
Expert FAQ
- A column has zip codes like "00501" — will auto-detection turn it into the number 501 and drop the leading zeros?
No — this converter never auto-detects types at all; every CSV value, including a zip code like "00501", is kept as the exact string it appeared as. There's no type-detection toggle to turn on or off, so leading zeros, phone-number formatting, and similar text-like numbers are always preserved as-is. - Does it turn a column header like "address.city" into a nested object, or keep it as a literal flat key?
Headers are always kept as literal flat keys — "address.city" becomes one key containing a literal dot, not a nested path. There's currently no option to expand dot-notation headers back into nested objects; if you need that, you'd have to restructure the JSON manually afterward. - What happens with a row that has fewer or more comma-separated values than the header row?
A short row (fewer columns than headers) produces missing keys for the unfilled columns rather than shifting subsequent values into the wrong fields — this is a common parsing bug when a converter naively zips headers to values by position without checking length first. A row with more values than headers usually means an unescaped delimiter inside a field. The extra values are kept in added extra_field_N columns rather than dropped or shifted, so the problem row is easy to spot and fix at the source. - My CSV opens fine in Excel but the JSON output has garbled characters at the start of the first key — why?
That's almost always a UTF-8 byte-order-mark (BOM) that Excel adds when saving CSV as "UTF-8". The BOM is an invisible character at the very start of the file that, if not stripped, ends up prepended to your first header name (turning "id" into something that looks like "id" but fails strict key-matching). This converter strips a leading BOM automatically before parsing headers.
Technical Details
Converting CSV to JSON means making several judgment calls that a spreadsheet's flat grid doesn't make explicit. Type detection (turning "42" into the number 42, "true" into the boolean true) is convenient but lossy in specific cases: values with leading zeros (zip codes, account numbers) lose those zeros once interpreted as a number, since JSON's number grammar has no leading-zero concept. This converter never performs type detection at all — every value stays a string, so this category of data-loss bug simply can't occur here (though it also means numeric fields need to be cast explicitly by your own code after conversion). Row/header alignment is done by length-checked pairing rather than naive zip-by-position: a row with fewer fields than the header row produces explicit missing keys for the unfilled columns, and a row with more fields than headers keeps the extra values in added extra_field_N columns (usually a sign of an unescaped delimiter or unbalanced quote upstream) rather than silently shifting every later value one column over. Two encoding-level details matter more than they should: a UTF-8 byte-order-mark, which Excel adds by default when exporting "CSV UTF-8," is stripped before header parsing so it doesn't corrupt your first column's key name; and values are unescaped per RFC 4180 quoting rules (doubled quotes inside quoted fields, embedded commas and newlines inside quoted fields) rather than naively splitting on every comma in the line. If your source CSV doesn't parse as expected, the CSV Validator can confirm whether the file itself is RFC 4180-compliant before you debug the conversion logic. After conversion, the JSON Formatter or JSON Viewer make the resulting structure easier to inspect.