JSON to NDJSON Converter
Drop a .json file or paste JSON below to instantly convert it to Newline Delimited JSON (.ndjson). Each array element becomes one line. Nothing leaves your browser.
About This Tool
The JSON to NDJSON Converter is a free online utility that transforms standard
.json files into Newline Delimited JSON (also known as NDJSON,
JSON Lines, or .jsonl) directly in your browser. Use this tool to convert JSON arrays
into a streaming-friendly format without installing software or uploading data to a server.
NDJSON is a widely adopted format for data pipelines, log ingestion, and machine learning datasets because each line is a self-contained, valid JSON object. Tools like Apache Spark, Elasticsearch, BigQuery, and many CLI utilities consume NDJSON natively. This converter handles JSON arrays of any size and maps every element to exactly one output line.
Because everything runs client-side using JavaScript and the Web File API, your files remain entirely private throughout the conversion process — no data is ever sent to a remote server.
Common Use Cases
- Prepare data for streaming pipelines — Turn a JSON array export into NDJSON so tools like Kafka, Logstash, or Fluentd can consume records one at a time.
- Load data into Elasticsearch or OpenSearch — The Bulk API requires NDJSON format; convert your JSON export in seconds before indexing.
- Build machine learning datasets — Many ML frameworks and dataset libraries (Hugging Face, TFDS) prefer JSONL/NDJSON for large record collections.
- Process files with command-line tools —
jq,xsv, and similar utilities work line-by-line, making NDJSON far easier to stream and filter. - Keep sensitive data local — Convert private or proprietary JSON without routing the file through any third-party server.
How It Works
.json file onto the tool, click Browse to pick one, or switch to the Paste tab and type or paste raw JSON directly.JSON.parse(), then iterates over each array element and serialises it back to a compact single-line string with JSON.stringify(), joining them with newline characters (\n)..ndjson file locally.What Gets Processed
- JSON syntax validation — The input is fully parsed before conversion; any malformed JSON is caught and reported as an error with the parser's own message.
- Array unwrapping — Top-level arrays are iterated element-by-element; each item (object, string, number, or nested array) becomes exactly one NDJSON line.
- Single-object handling — If the root value is a JSON object rather than an array, it is written as a single NDJSON line and a warning is shown so you know the behaviour.
- Whitespace stripping — All indentation and pretty-printing is removed during
JSON.stringify(), producing compact lines suitable for line-oriented processing. - Unicode preservation — The converter reads files with
TextDecoder(UTF-8) and writes the download as a UTF-8 Blob, so multi-byte characters are preserved exactly.
🔒 Privacy & Security
All processing is performed locally using the Web File API and JavaScript ArrayBuffer. Your file is never sent to a server — suitable for sensitive or private content.