NDJSON to JSON
This converter merges NDJSON (JSON Lines) into a single JSON array. Each line is parsed on its own and appended to the array in file order, so the result can be read with JSON.parse or sent to an API that only accepts an array. Indentation and key sorting are configurable, and the conversion runs entirely in your browser — nothing is uploaded.
How to use it
- 1
Paste your NDJSON
Drop line-delimited JSON into the editor, or pick a local .jsonl file. The data is read on your machine only.
- 2
Choose an output indent
Select 2 spaces, 4 spaces or a tab, or keep the output compact as a single line.
- 3
Let it merge automatically
About 400ms after you stop typing it parses each line in a Web Worker and merges them into one array.
- 4
Copy the result
Copy the JSON array in one click, or flip the direction to split the array back into NDJSON.
Key features
Line-by-line merging
Every line is parsed on its own and appended in order; an invalid line reports its line number instead of failing the whole document.
Indent and key sorting
Beautify or minify the array and recursively sort keys for stable, easy-to-compare output.
Reversible in one page
The same page converts a JSON array back to NDJSON, so you never have to switch tools.
Order is preserved
The array keeps the exact order of the input lines.
Local and private
Parsing runs in a Web Worker in your browser; nothing is uploaded.
Handles large logs
Worker-based parsing keeps multi-megabyte log files responsive.
Common errors & troubleshooting
- ! The input must be one JSON value per line; if you have a single multi-line JSON document, minify it first or use the reverse mode.
- ! Blank lines are skipped by default, and leading or trailing whitespace on a line does not affect parsing.
- ! If one line fails, the error names the line number and the reason — fix that line and the array is recomputed automatically.
- ! A trailing newline at the end of the file is harmless; it is treated as a blank line and ignored.
Frequently asked questions
Does the array keep the same order as the file?
Yes. Elements are appended in exactly the order the lines appear.
What happens if one line is not valid JSON?
The tool reports the specific line number and reason, and recomputes once you fix it. You can also check for hidden blank lines if you expect more records.
Can I convert the array back to NDJSON?
Yes — flip the direction on the same page to split the JSON array into one record per line. The two tools are inverse operations.
Is my data uploaded?
No. The conversion runs locally in your browser; nothing leaves your device.
Related tools
JSON to NDJSON
Split a JSON array into line-delimited NDJSON (JSON Lines) — one record per line — for logs, streaming APIs and bulk imports.
NDJSON Formatter
Format and validate NDJSON / JSON Lines. Each line is parsed independently: valid input is pretty-printed per record with a count, and any bad line reports its exact line and column.
JSON Formatter
Format, beautify and validate JSON in your browser. Errors point to the exact line and column, and you can indent with 2 spaces, 4 spaces or a tab.