What is a NDJSON file?
NDJSON — JSON Lines
What is it?
NDJSON stores one complete JSON object per line, with no enclosing brackets and no commas between lines. Each line can be read independently of the others.
This matters a great deal for large volumes of data: a standard JSON file must be loaded entirely into memory before it can be used. An NDJSON file can be read line by line — so a 50 GB file can be processed on a machine with only 8 GB of memory.
History & origin
The convention emerged naturally as streaming data processing grew, once data volumes made loading an entire file into memory impractical.
It became the de facto format for application logs and exports from large databases.
Why it is useful
It can be processed as a stream, line by line, regardless of the file's total size.
A corrupted line doesn't invalidate the rest of the file — unlike standard JSON, where a single misplaced comma renders the whole file unusable.
Limits & drawbacks
It isn't strictly valid JSON: a standard parser will reject it.
It has no official specification, which leaves room for variants.
Practical tips
NDJSON is well suited to logs, large-scale exports, and data streams.
To open it in a spreadsheet, convert it to CSV — provided the structure is flat.
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