What is a NDJSON file?
NDJSON — JSON Lines
Use the format NDJSON
A concrete example
Prepare a JSON table from an NDJSON log.
Useful checks
Each line must be a valid JSON. Check empty lines, isolated errors, and the size of the aggregated result.
Choose a conversion
Keep the original and open the result in the software or on the device that will need to use it.
Your questions about this format
Why does my JSON change structure when converted to CSV?
CSV represents a table of rows and columns. JSON can contain objects and nested lists that do not transpose directly. Convert a copy, check how the fields are represented, and keep the JSON if your usage requires retaining its entire structure.
How can one avoid losing the leading zeros in identifiers?
When opening the CSV in a spreadsheet, import the identifier columns as text. Automatic opening can turn 00123 into 123. Also check the dates and decimal separators before re-saving.
Can I convert a file containing secrets?
Remove passwords, API keys, and other secrets before sending a sample to the service or support. File processing is done online. For data that must not leave your device, use a suitable local tool.
Why aren't all outputs offered?
Formats are not interchangeable in all cases. ConvertLab displays the conversions from its catalog; renaming an extension does not change the content. Specialized outputs like certain XML exports or spreadsheets are identified as NoLimit.
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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