CSV to JSON Converter (and JSON to CSV)

How the conversion works

name,address.city,age,zip,tags
Ana,Lisbon,31,01100,"[""a"",""b""]"
"Lee, Jo",Seoul,,04524,[]

[
  { "name": "Ana",
    "address": { "city": "Lisbon" },
    "age": 31, "zip": "01100",
    "tags": ["a", "b"] },
  { "name": "Lee, Jo",
    "address": { "city": "Seoul" },
    "age": "", "zip": "04524",
    "tags": [] }
]

CSV to JSON

• The first row gives the names of the fields. Empty names become column_3, and a repeated name gets a number (name_2), so no value is lost.
• Numbers, true/false and null become real JSON values. Values with a leading zero (01100), a plus sign or more than 15 digits stay text, because they are codes, not amounts. A cell that holds a JSON array or object, such as ["a","b"], is read as JSON.
• A header with a dot, such as address.city, makes a nested object. Turn "Nested keys" off to keep the dot in the key name.
• Empty cells become "", null or no key at all, as you choose. Empty lines are skipped.
• A row with more or fewer cells than the header is still converted, and the status line tells you which lines they are.

JSON to CSV

• The input can be an array of objects, an array of arrays, one object, an object whose values are objects (each one becomes a row, with its name in a key column), or JSON Lines (one object per line). If the array sits inside a wrapper such as {"data": [...]}, it is found.
• Every key that appears in any object becomes a column, in the order it first appears. Missing values give empty cells.
• Nested objects become a.b columns; arrays are written as JSON text in one cell. null gives an empty cell.
• Numbers are written exactly as they are in your JSON, so 12345678901234567890 and 1.50 do not change.

The CSV format in short (RFC 4180)

CSV has no single official standard, but RFC 4180 describes what almost every program reads and writes:

1. Each record is one line. Fields are separated by a comma (or another delimiter).
2. A field that contains the delimiter, a double quote or a line break is put in double quotes: "Lee, Jo".
3. A double quote inside a quoted field is written twice: "She said ""hi""" means She said "hi".
4. A quoted field may contain line breaks, so one record can cover several lines of the file.
5. Spaces belong to the field. a, b gives the second field " b" with a space in front.

TSV (tab-separated values) is the same idea with a tab between fields; it is what you get when you copy cells from Excel or Google Sheets. JSON Lines (also called NDJSON) puts one JSON object on each line, which is common for logs and for large exports, because a program can read it line by line.

CSV files and Excel: common problems

Convert CSV and JSON in code and on the command line

Splitting a line on every comma (line.split(',')) is the most common CSV bug: it breaks as soon as a field contains a quoted comma or a line break. Use a real CSV parser, like the ones above or this page.

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