About JSONL / NDJSON Validator & Converter
JSONL (also called NDJSON, or JSON Lines) stores one JSON value per line, separated by newlines. It's the default shape for log streams, machine-learning datasets, database exports, and any pipeline that appends records one at a time — because each line stands alone, tools can read, write, and stream the file without loading it all into memory.
This free JSONL validator and converter checks every line independently, so a single malformed record is flagged by line number instead of breaking the whole file. It also converts JSONL into a pretty-printed JSON array and turns a JSON array back into compact JSONL. Everything runs entirely in your browser — your data is never uploaded.
Features
- Validate JSONL / NDJSON line by line, with the exact line number of each bad record
- Convert JSONL to a formatted JSON array
- Convert a JSON array back to compact one-object-per-line JSONL
- Fully offline — your data never leaves the device
How to use
- Paste your JSONL (or a JSON array) into the input pane.
- Choose Validate to check each line, JSONL → Array to build a JSON array, or Array → JSONL for the reverse.
- Copy the result from the output pane — or clear and start again.
Frequently asked questions
What is the difference between JSONL and JSON?
A JSON file is one value — usually a single array or object. JSONL is many independent JSON values, one per line, with no enclosing array and no commas between records. That makes JSONL easy to stream and append line by line.
Is JSONL the same as NDJSON?
Effectively yes. JSON Lines (JSONL), NDJSON (Newline-Delimited JSON), and ".jsonl" exports all describe the same format: one valid JSON value per line. This tool treats them interchangeably.
Why does one bad line not fail the whole file?
Because each line is parsed on its own. When validating, every non-empty line is checked independently and any failures are reported with their line number, so you can fix records without re-validating the rest.
Does my data get sent anywhere?
No. All validation and conversion happens locally in your browser using the built-in JSON parser. Your input never leaves your device.
Related tools
Everything runs locally in your browser — your input is never uploaded.