Online Tool Store
JSONL Dataset Formatter
Paste a JSON array of records and convert it to JSONL, the standard format for ML training datasets. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
JSONL output
{"prompt": "Hello", "completion": "Hi there!"}
{"prompt": "Bye", "completion": "See you later!"}Example shown — replace it with your own JSON array of records.
How it works
- Paste a JSON array of records.
- Each array element is written to its own line as valid JSON.
- Copy or download the resulting JSONL file.
Conversion parses the JSON array, then writes each element with
JSON.stringify() on its own line — the exact JSON
Lines format expected by dataset loaders and fine-tuning pipelines.
FAQ
Is my dataset uploaded anywhere?
No. Conversion happens entirely in your browser — your data is never sent to a server.
What is JSONL used for?
JSON Lines (one JSON object per line) is the standard format for machine learning training datasets and fine-tuning files, including OpenAI's fine-tuning format.
Can I convert from JSONL back to a JSON array?
Yes — paste JSONL input and the tool wraps each line back into a single JSON array.
Does it validate each record?
Yes — each line is checked as valid JSON before being included, and any malformed records are flagged instead of silently passed through.
How we compare
| Feature | Online Tool Store | Python one-liner | jq (CLI) |
|---|---|---|---|
| No install, works in any browser | ✓ | Requires Python installed | Needs a terminal + install |
| Free, no setup | ✓ | ✓ | ✓ |
jq handles this well but needs a terminal and syntax to remember. JSONL Dataset Formatter is a paste-and-convert shortcut for the common case.