CSV to JSON

How it works

Files are read with the browser's FileReader API and parsed by a hand-written single-pass parser that follows RFC 4180 rules: it walks the text character by character while tracking whether it's inside a quoted field. That's the part naive split-on-comma converters get wrong: inside quotes, commas and even line breaks belong to the cell, and a doubled quote ("") is a literal quote character. Delimiter auto-detection is pragmatic rather than clever: it counts commas, semicolons, and tabs in the first line and picks the winner, which handles the semicolon-delimited CSVs that European Excel exports produce.

Type coercion is where you should look twice at the output. Values that look like integers or decimals become JSON numbers, and true/false become booleans. That's usually what you want, but it means values with leading zeros, like ZIP codes or phone extensions, come out as numbers: 01234 turns into 1234. If a column is an identifier rather than a quantity, verify it after converting. Missing trailing cells in short rows become empty strings rather than crashing the row.

Parsing, coercion, and even the .json download (built from an in-memory Blob) all happen inside this page's JavaScript. Open DevTools' Network tab while converting: no request carries your data, so customer lists and exports never leave your machine.