NDJSON

NDJSON (Newline-Delimited JSON) is an informal specification published at ndjson.org for a line-delimited JSON format. Each line contains one valid JSON value, separated by a line feed (\n) or carriage-return-line-feed (\r\n).

In practice, NDJSON is the same format as JSONL. Tools generally accept either name and either file extension (.ndjson or .jsonl). The two specs differ only in minor details — NDJSON traditionally allows \r\n as a line separator, JSONL insists on \n only. Most consumers do not care.

Example

{"timestamp": "2026-04-23T12:00:00Z", "level": "info",  "msg": "server started"}
{"timestamp": "2026-04-23T12:00:01Z", "level": "debug", "msg": "route matched"}
{"timestamp": "2026-04-23T12:00:05Z", "level": "error", "msg": "db timeout"}

Each record is independent. A log viewer can start at line 1,000,000 without knowing anything about lines 1 through 999,999.

Reading NDJSON

Same recipe as JSONL: split the input stream on newlines, parse each non-empty line as JSON.

for line in f:
    line = line.strip()
    if line:
        record = json.loads(line)
        process(record)

Trade-offs

The format shines when records are small and the stream is long. It loses its advantage when individual records are so large that they themselves span many line-worth of bytes — line-delimited parsers assume lines are reasonably sized.

For a full comparison with standard JSON and the streaming alternatives, see the guide JSONL, NDJSON, and JSON Lines explained.