NDJSON / JSONL Converter
Lines ↔ array · Validate rows · Local
YAML Conversion
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ABOUT
About NDJSON / JSONL Converter
NDJSON (JSON Lines) is one JSON value per line. This page converts a line stream to an array, an array back to lines, or reports which lines fail to parse.
Use it for log exports, eval sets, and streaming APIs. Formatter still treats input as a single document.
DEEP DIVE
NDJSON / JSONL Converter
LLM fine-tunes and Elasticsearch dumps often arrive as .jsonl. Pasting that into Formatter fails because two objects cannot sit side by side in one JSON text.
Validate mode lists line numbers and parse errors. Samples use fictional order ids (A-1042), never live secrets.
FEATURES
NDJSON / JSONL Converter
JSONL → JSON
Skip empty lines; emit a JSON array.
JSON → JSONL
Each array element becomes one compact line.
Validate lines
Report line number and parse error.
Local files
Drag .ndjson / .jsonl — nothing is uploaded.
Not Formatter
Single-document beautify stays on the Formatter page.
Pairs with Flatten
Flatten objects after you have an array.
HOW TO USE
How to use
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1
Paste JSONL or a JSON array.
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2
Pick JSONL → JSON, JSON → JSONL, or Validate lines.
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3
Fix any reported bad line.
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4
Copy or export the result.
FAQ
FAQ
Is this JSON Formatter?
No. Formatter parses one document. This page is one value per line.
Are blank lines errors?
They are skipped.
Can a line be an array or number?
Yes. Each line is any JSON value.
Do you keep key order?
JSON.stringify uses engine defaults; treat this as a data conversion, not pretty-print.
Is data uploaded?
No.
What about concatenated JSON without newlines?
Use Formatter Auto Fix for glued objects; this page expects line breaks.