File extension

.ndjson

Newline Delimited JSON (NDJSON / JSON Lines)

.ndjson files are Newline Delimited JSON files: text files containing one JSON value per line, also known as JSON Lines (.jsonl), suited to streaming and log-style data.

Known meanings

Formats and reference material for .ndjson

Newline Delimited JSON (NDJSON / JSON Lines)

Text format with one JSON value per line, used for streaming and record-oriented data (also .jsonl)

  • data-format internet
  • NDJSON specification contributors
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Details

Format notes

Newline Delimited JSON (NDJSON)

NDJSON is a convention for storing a sequence of JSON values in a text file or stream, with exactly one value per line, usually a JSON object. A closely related convention, JSON Lines, uses the extension .jsonl and the same layout; the two are, for practical purposes, interchangeable.

Each line must be a valid, self-contained JSON text, and lines are separated by a newline character (\n, with \r\n tolerated by parsers). Because records are separated by line breaks, a JSON value on a line may not contain raw newlines (they appear escaped as \n inside strings). This is what distinguishes NDJSON from a single JSON array: a file can be read, filtered, split, or appended to one record at a time without parsing the whole document.

Adoption

NDJSON is widely used for log files, data exports, and streaming APIs. Many databases and analytics tools import and export it, and command-line tools such as jq process it line by line. The encoding is UTF-8. A commonly used media type is application/x-ndjson.

Preservation And Security Notes

Plain-text, line-oriented files are easy to inspect, compress, and diff, which suits long-term storage, but NDJSON has no schema or type enforcement, so records in one file can have differing structures. Consumers should handle malformed lines and very long lines defensively, and apply the usual JSON precautions (deeply nested input, duplicate keys, and number precision) when parsing untrusted data.

Further Reading

  • NDJSON specification: https://github.com/ndjson/ndjson-spec
  • JSON Lines: https://jsonlines.org/