JSONL ↔ JSON Array Converter

updated 25 April 2026

100% client-side. Files stay in your browser.

Before you start

You need either a JSONL file (where each line is a standalone JSON object) or a standard JSON file containing a single array. I built this tool to be bi-directional because I often find myself needing to wrap streaming logs into a single array for a quick script, or conversely, unwrapping a giant export to feed into an LLM fine-tuning pipeline.

If you are converting JSONL → JSON array, make sure every line in your input is valid JSON. This tool is pretty forgiving and will skip empty lines, but a single malformed line will trigger an error.

There is no hard file size limit since everything happens in your browser's memory. For files over 100 MB, I recommend setting the indent to 0 to avoid the massive memory overhead of generating a pretty-printed string that might crash your tab.

How to use it

1. Paste your data into the Input pane, or drag and drop a .jsonl or .json file directly onto the page.
2. Adjust the Indent value — use 2 or 4 for readability, or 0 for a compact, minified result.
3. Click JSONL → JSON array to wrap lines into a single [...] block, or JSON array → JSONL to unwrap an array into line-delimited objects.
4. Check the status bar at the bottom to see the record count or any parsing errors.
5. Use Copy to grab the text or Download to save the result as a file.

Options explained

Indent

This controls the JSON.stringify indentation level. When converting to a JSON array, it creates a pretty-printed structure that is easy for humans to read. When converting to JSONL, it applies that same indentation to each individual line. Usually, for JSONL, you want this at 0 to keep every record on exactly one line, which is what most APIs expect.

The Conversion Buttons

Because this tool works both ways, you have to tell it which direction to go. JSONL → JSON array looks for lines of text and wraps them. JSON array → JSONL parses the entire input as one big JSON blob, verifies it's an array, and then iterates through the items to write them out line-by-line.

Example

Input (JSONL):

{"id": 101, "status": "ok"}
{"id": 102, "status": "error"}

Output (JSON array, Indent: 2):

[
  {
    "id": 101,
    "status": "ok"
  },
  {
    "id": 102,
    "status": "error"
  }
]

Tips & common pitfalls

• Empty lines are ignored. When going JSONL → JSON, I skip whitespace-only lines so you don't get null entries in your array.
• Key order is preserved. Modern JavaScript engines maintain the insertion order of string keys, so your objects won't be "shuffled" during the round trip.
• Nested arrays are fine. If your JSONL contains arrays instead of objects, the tool handles them perfectly. The only requirement is that each line is valid JSON.
• Large files and Indent. If you are converting a 50 MB file and use an indent of 2, the resulting string can easily double or triple in size due to the extra whitespace. Use 0 for big datasets.

Troubleshooting

Related tools

• JSONL ValidatorFind malformed lines in your NDJSON files.
• JSONL ViewerInspect and filter JSONL records in a searchable table.
• JSONL to CSVFlatten nested JSONL objects into a spreadsheet format.
• OpenAI ValidatorCheck your JSONL against the chat-completion schema.

See also: if you need to do something adjacent on this site, try JSONL to CSV to flatten JSONL into a CSV with dotted keys, Formatter to pretty-print or minify each JSONL record, or OpenAI Fine Tune Validator to validate an OpenAI fine-tune file against the chat schema.

Frequently asked questions