JSON Generator — Build Arrays from Columns

Give each field a key name and enter one value per line. Values on the same line number become one object in the output array. The field with the most lines determines the number of records; shorter fields are padded with null.

Use this tool to prepare API test fixtures or mock data without typing JSON punctuation. It creates a flat array of objects from your input, not random data.

Integers, decimals and exponent notation, such as 123, -4.5 and 1e10, become JSON numbers. Lowercase true and false become booleans. Blank lines and null become null. Other values remain strings; 007 keeps its leading zeros.

Type detection trims surrounding whitespace. Strings retain their original whitespace. Quotes, arrays and objects entered as values are treated as literal text, not parsed JSON. CSV quoting and delimiters are not interpreted. There is no option to force numeric-looking values to strings.

Number notation is preserved in the output, including large integers and exponents. A JSON reader may round numbers or exceed its supported range or precision; keeping the notation does not guarantee exact values in the receiving application.

Create keys name, price and active. Enter Apple and Orange on separate lines under name, 1.20 and 1.50 under price, and true and false under active. Compact output is:

[{"name":"Apple","price":1.20,"active":true},{"name":"Orange","price":1.50,"active":false}]

The prices are example numbers with no currency implied. Choose Compact, 2 spaces or 4 spaces, then generate and copy the result. Editing an input or changing the format clears the old result so you can generate an updated version.

Use invented names, addresses and identifiers rather than real customer or personal data. Numeric-looking identifiers are often best represented as strings. Leading-zero values such as 00123 remain strings here, but adding zeros or quotes changes the value itself. For identifiers such as 12345 that must be strings, edit the generated JSON in the JSON Formatter & Validator.

Key names are trimmed and must be unique. A field containing values needs a key name. A named field with no entered value produces one null; a trailing newline adds another null record.

The limits are 100 keys, 1000 lines per field, 128 characters per key name, 20000 characters of values per field, 100000 input characters in total and 500000 output characters. Character counts use UTF-16 code units. Split large inputs into batches; Compact can reduce output size.

If copying fails, retry or use Select output to copy manually. While a copy is pending or its completion is unconfirmed, avoid other copy operations: a late operation could overwrite the clipboard with older content. The warning remains until that operation settles.