JSON to CSV

CSV is what spreadsheets and most analysis tools import, which makes this the conversion to reach for when an API response has to go to someone who works in Excel, Numbers, or Sheets. It is also the most lossy conversion on this site, because a tree does not fit in a grid without decisions being made for you.

Those decisions: a nested object becomes dotted columns, so address.zipCode is a header rather than a structure. Records missing a field still line up under the right headers instead of shifting left. An array of plain values shares one cell, joined with ; , because there is no column to spread it across. The union of every record's keys becomes the header row, so a field present in only one record still gets a column.

Quoting follows RFC 4180 — any cell containing the delimiter, a quote, or a newline is wrapped, and an internal quote is doubled — with one addition aimed at spreadsheets rather than parsers.

My JSON is a single object, not an array. Why the error?

CSV rows are records, so the input has to be an array of them. Wrap a lone object in brackets for a one-row file. If your payload is {"items": [...]}, convert the array itself rather than the wrapper.

Why is a cell starting with = or + quoted?

Because Excel, Sheets, and Numbers treat a leading =, +, -, or @ as the start of a formula. Without the quotes, a value of -5 becomes a calculation and =SUM becomes an error in the cell. This is not a CSV rule — it is the difference between a file that parses and a file that opens correctly.

What happens to a deeply nested array of objects?

It is flattened by index, with bracket notation: projects[0].title, projects[1].title, and so on. Honest, but it means a record with twenty items produces twenty sets of columns — usually the signal that CSV is the wrong target for that payload.

Can I convert the result back?

Structurally, no. Dotted headers do not rebuild into nested objects on the way back, and a cell holding a; b is a string rather than an array. Treat CSV as a hand-off format, not a storage one.