JSONL Output
JSONL Output will appear here
Paste a JSON array on the left to get one compact record per line.
Try it with two chat-style training records
JSON to JSONL
Free JSON to JSONL converter: paste a JSON array and get JSON Lines, one compact record per line. Switch direction to turn a .jsonl file back into a JSON array.
How to Convert JSON to JSONL
This JSON to JSONL converter turns a JSON array into JSON Lines in three steps, and the same tool converts JSONL back to JSON when you need the array again.
1
Paste a JSON array (or open a .json file)
Paste your data into the left editor, or use the upload button to open a .json file. The JSON to JSONL conversion expects a JSON array. If you have a single object, it is written as a one-line file and the tool tells you so. Not sure the input is valid? You can validate the JSON first.
Paste or upload - Paste a JSON array or open a .json file from your device.
Runs in your browser - The JSON you paste is converted locally and never uploaded.
Sample JSON array (input)
[
{
"messages": [
{
"role": "user",
"content": "What is JSONL?"
},
{
"role": "assistant",
"content": "One JSON value per line."
}
]
},
{
"messages": [
{
"role": "user",
"content": "Is NDJSON different?"
},
{
"role": "assistant",
"content": "No, same format."
}
]
}
]2
Check the record count and any errors
Every array element becomes one line of the output, in the original order, and the status bar shows how many records were written. Invalid JSON is reported with its position, and no half-finished output is shown. The sample on the right is the JSON to JSONL conversion of two chat-style training records.
Record count - The status bar shows how many lines were written.
Clear errors - Invalid JSON is reported with its position.
JSON to JSONL output (one record per line)
{"messages":[{"role":"user","content":"What is JSONL?"},{"role":"assistant","content":"One JSON value per line."}]}
{"messages":[{"role":"user","content":"Is NDJSON different?"},{"role":"assistant","content":"No, same format."}]}3
Download the .jsonl file
When the JSON to JSONL conversion is done, copy the lines or download them as a .jsonl file. Each line is a compact JSON value and the file ends with a newline.
Download .jsonl - Save a timestamped file that ends with a newline.
Copy lines - Copy the JSON Lines to your clipboard.
Copy or download the JSON to JSONL result
2 Actions
Download
Save as json-to-jsonl-<date>.jsonl
Copy
Copy JSONL to clipboard
Tip: switch the direction to JSONL → JSON to turn the lines back into an array.
What Is JSONL (JSON Lines / NDJSON)?
JSONL, JSON Lines and NDJSON (newline-delimited JSON) are three names for one text format. A file holds one complete JSON value per line, usually an object, and the lines are separated by a newline character. The encoding is UTF-8. A JSON to JSONL converter such as this one simply writes every element of your array on its own line.
JSONL vs JSON: when to use each
A normal JSON file is one document, so a program must read all of it before it can use any record. A JSONL file can be read, filtered and appended to one record at a time, which suits logs, exports and datasets that are too large to hold in memory. Use plain JSON for API responses and configuration, and JSONL for streams of records.
The rules of the format
- Each line is one complete JSON value; a record cannot span several lines.
- There are no square brackets around the file and no commas between lines.
- Lines end with
\n(a\r\nending is tolerated by most readers). - Newlines inside strings are written as the escape sequence
\n, never as a real line break.
Convert JSONL Back to a JSON Array
Switch the direction to JSONL → JSON and paste or open your lines. Each non-empty line is parsed on its own, and the records are collected into one array with two-space indentation. Windows line endings and a leading byte order mark are handled, and blank lines are ignored.
Blank lines and invalid records
If a line is not valid JSON, the converter stops at the first one and shows its line number, so you can fix exactly that record. Turn on Skip invalid lines if you would rather keep the valid records and see how many were left out. In this example the second line is missing its closing brace:
Broken JSONL (line 2 has no closing brace)
{"id":1,"event":"login"}
{"id":2,"event":"click"
{"id":3,"event":"logout"}The converter reports an error on line 2, and the empty third line is ignored.
Common Uses for JSON Lines
Preparing fine-tuning and batch files for LLMs
Many language-model tools take training examples and batch requests as JSONL, one example per line. JSON to JSONL conversion is often the step that prepares them, and this converter only changes the format. Check the required fields and file limits against the documentation of the platform you upload to.
Bulk loading into data warehouses
Warehouses such as BigQuery can load newline-delimited JSON, so a quick JSON to JSONL conversion of an exported array is often the first step of an import.
Logs and streaming pipelines
JSON to JSONL conversion also suits logs: because each line stands alone, log shippers and stream processors can append new records without rewriting the file, and a broken line only affects that one record.
Command-Line Alternatives (jq and Python)
If you prefer the terminal, these commands do the same JSON to JSONL conversion and its reverse:
jq
# JSON array -> JSONL
jq -c '.[]' in.json > out.jsonl
# JSONL -> JSON array
jq -s . in.jsonl > out.jsonPython
# Python: JSON array -> JSONL and back
import json
with open("in.json", encoding="utf-8") as src, open("out.jsonl", "w", encoding="utf-8") as dst:
for record in json.load(src):
dst.write(json.dumps(record, ensure_ascii=False) + "\n")
with open("out.jsonl", encoding="utf-8") as src:
records = [json.loads(line) for line in src if line.strip()]
with open("back.json", "w", encoding="utf-8") as dst:
json.dump(records, dst, ensure_ascii=False, indent=2)Related Tools
- Need the records in a spreadsheet? Switch to JSONL → JSON first, then paste the array into JSON to CSV or JSON to Excel. Those converters read one JSON document, not raw JSON Lines.
- Want to browse the records as rows and columns? Convert the lines to a JSON array here, then view the array as a table.
- Working with a huge file? Split a large JSON file into smaller files. Note that splitting a file into several files is different from this tool, which splits an array into lines.
JSON to JSONL FAQs
Common questions about JSON Lines, NDJSON and converting between JSON and JSONL
To convert JSON to JSONL, paste a JSON array into the left editor, or upload a .json file. Each element of the array is written as one compact JSON value on its own line, in the original order, with no brackets around the whole file and no commas between lines. Check the record count under the output, then use Copy or Download to save the result as a .jsonl file.
They are three names for the same format: one complete JSON value per line, separated by newline characters and encoded as UTF-8. The file extension is usually .jsonl or .ndjson. This JSON to JSONL converter reads and writes that format, so a file you create here works wherever any of the three names is accepted.
A JSON file is a single document, so a parser has to read all of it before it can use any of it. A JSONL file is many small JSON documents, one per line, so a program can read, append or process it one record at a time. That is why logs, data exports and training datasets often use JSONL, while API responses and configuration files use plain JSON.
Yes. Switch the direction to JSONL to JSON and paste or upload your lines. Every non-empty line is parsed on its own and the records are collected, in order, into one JSON array with two-space indentation. Blank lines are ignored, and Windows (CRLF) line endings and a leading byte order mark are handled.
The converter stops and shows the number of the first invalid line together with the parser message, so you can find and fix that record. If you only need the valid records, turn on Skip invalid lines. The converter then leaves out the broken lines and tells you how many it skipped.
Yes, in two steps. Switch the direction to JSONL to JSON here to collect the lines into one JSON array, then paste that array into the JSON to CSV converter or the JSON to Excel converter. Those converters read a single JSON document, so JSON Lines with more than one line pasted there directly show a syntax error.
Yes. In a JSON to JSONL conversion, a single object, or any single JSON value, becomes a file with one line, and the converter tells you that the input was a single value. If your records sit inside a larger object, for example under a data or items key, paste just that array to get one line per record.
For JSON to JSONL conversion of fine-tuning data, put each training example in one object, for example an object with a messages array of role and content entries, collect the objects into a JSON array and convert it here. Each example becomes one line. This tool only changes the format; check the field names and limits against the current fine-tuning documentation of the platform you use.
No. This JSON to JSONL converter is plain JavaScript that runs in your browser tab, so the JSON you paste or open never leaves your device and nothing is sent to a server for processing. You can check this in your browser developer tools, where converting a document does not create any network request.
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