JSON to CSV & CSV to JSON Converter

Converting a JSON array to CSV works best when it is an array of objects, which is the shape most APIs and databases export. Every distinct key becomes a column, in the order it's first seen, so objects with missing fields still line up and leave those cells empty. A single object becomes one row, an array of arrays is written row by row, and an array of plain values becomes a single value column.

CSV has no concept of nesting, so nested objects need a decision. With flattening on, {"address": {"city": "Paris"}} becomes a column named address.city. With it off, the whole object is written as a JSON string in one cell. Arrays are always written as JSON strings, because spreading them over numbered columns rarely survives a round trip. In the other direction, headers containing dots are rebuilt into nested objects, so a file you flattened comes back with its original structure.

Quoting follows RFC 4180, the closest thing CSV has to a standard. A field is wrapped in double quotes if it contains the delimiter, a quote, a line break or leading or trailing spaces, and quotes inside it are doubled. The parser accepts the same rules, including quoted fields that span several lines, CRLF or LF line endings, and the byte-order mark Excel adds. An unclosed quote is reported with the line it started on.

When detecting types, 42 and 9.5 become numbers, true and false become booleans, null becomes null, and a cell holding a JSON array or object is parsed back into one. Values that would lose information stay as strings: 007 keeps its leading zeros, and integers too large for JavaScript's number type, like long IDs, aren't rounded. Untick 'Detect numbers & booleans' to keep every value as a string.