Convert CSV to JSON

Spreadsheets export CSV; code, APIs and databases want JSON. This converter reads CSV the way the RFC 4180 standard describes it: fields in double quotes may contain commas, line breaks and doubled quotes ("" for a literal quote), lines can end in Windows CRLF or Unix LF, and a byte-order mark from Excel is ignored. Each row becomes an object whose keys come from the header row, or an array of values if you prefer rows.

The delimiter is detected from the first lines, so semicolon-separated files from European Excel, tab-separated exports and pipe-delimited logs work without changing a setting. With type detection on, numbers become JSON numbers and true/false become booleans, but anything that only looks numeric is left alone: postcodes and phone numbers with leading zeros, values with a plus sign or a decimal comma, and integers too large to be exact in JavaScript all stay strings, so no data is quietly corrupted. Empty cells can become empty strings, null, or be left out.

Real-world files are messy, and the output tells you so instead of guessing silently. Rows with fewer fields than the header get empty values; rows with more get extra column_N keys; blank or repeated header names are renamed (column_2, name_2) and counted in a note. An unclosed quote stops the conversion with the line and column where it started. The conversion runs entirely in your browser, which matters for customer lists and exports that should not be uploaded anywhere.