CSV to JSON
Paste CSV text or open a file. If first row is the header is ticked, each later row becomes an object whose keys are the column names; otherwise the keys are column1, column2 and so on. The delimiter is detected automatically (comma, semicolon, tab or pipe) and you can set it by hand. Quoted cells can contain commas, quote marks (written twice) and line breaks. With turn numbers and true/false into JSON values on, plain numbers and booleans are real JSON values; things that only look like numbers, such as 007 or 1.50, stay text so no information is lost.
JSON to CSV
Paste a JSON array of objects, such as [{"a":1},{"a":2,"b":3}]. The columns are all the keys, in the order they first appear, and a missing key becomes an empty cell. Nested objects and lists are written as JSON text inside the cell. An array of arrays becomes rows with no header.
Questions
Is my data uploaded? No. The conversion happens in your browser, so private data stays on your device (files up to 5 MB). Why does my spreadsheet show strange text? Open the CSV as UTF-8 text, or use import instead of double-clicking. To tidy or check the JSON, use the JSON Formatter.