NDJSON Converter

What is NDJSON?

NDJSON (Newline Delimited JSON), also called JSONL (JSON Lines), is a text format where each line is a complete, valid JSON object. Unlike a regular JSON array, there is no wrapping [ ] and no commas between records — just one JSON object per line.

NDJSON example:

{"id": 1, "name": "Alice", "role": "admin"}
{"id": 2, "name": "Bob", "role": "user"}
{"id": 3, "name": "Carol", "role": "user"}

Equivalent JSON array:

[
  {"id": 1, "name": "Alice", "role": "admin"},
  {"id": 2, "name": "Bob", "role": "user"},
  {"id": 3, "name": "Carol", "role": "user"}
]

NDJSON vs JSON — When to Use Each

How to Convert NDJSON to JSON

1. Click "Open NDJSON Converter" above
2. Paste your NDJSON data (one JSON object per line)
3. Select "NDJSON → JSON Array" mode
4. Click Convert — the output is a standard JSON array
5. Copy or download the result

To go the other direction (JSON array to NDJSON), select "JSON Array → NDJSON" mode and paste your JSON array.

Frequently Asked Questions

What file extension does NDJSON use?

NDJSON files use the .ndjson or .jsonl extension. Both are identical in format. Google BigQuery documentation uses .ndjson, while the JSON Lines specification uses .jsonl. Most tools accept both extensions.

How do I parse NDJSON in Python?

Read the file line by line and parse each line as JSON:

import json
with open('data.ndjson') as f:
    records = [json.loads(line) for line in f if line.strip()]

How do I parse NDJSON in JavaScript / Node.js?

const records = fs.readFileSync('data.ndjson', 'utf8')
  .split('\n')
  .filter(line => line.trim())
  .map(line => JSON.parse(line));

Why does BigQuery require NDJSON instead of JSON?

BigQuery processes data in parallel across many workers. NDJSON allows each worker to read a chunk of lines independently without needing to parse the entire file structure first. A JSON array requires knowing where the array starts and ends, which prevents efficient parallel processing of large files.

What is NDJSON (Newline Delimited JSON)?

NDJSON (Newline Delimited JSON), also known as JSONL (JSON Lines), is a plain-text data format where each line contains exactly one complete, self-contained JSON value — typically a JSON object. The file has no wrapping structure: no outer array brackets, no commas between records, and no shared root element. Every line is independently parseable.

This design makes NDJSON the preferred format for streaming, logging, and large dataset processing because:

• You can append new records by simply writing a new line — no need to parse and rewrite the entire file.
• You can stream and process one record at a time without loading the entire file into memory.
• You can split large files at any line boundary and process chunks in parallel safely.
• A partial write or network cut only affects the current line — all previous lines remain valid.

NDJSON is defined at ndjson.org and uses the file extension .ndjson. The identical JSON Lines specification at jsonlines.org uses the extension .jsonl. The two formats are completely interchangeable.

How to Convert NDJSON to JSON Array

Converting NDJSON to a JSON array is straightforward: read each non-empty line, parse it as a JSON object, and wrap all the objects inside a [ ] array. The resulting JSON array is the standard format accepted by most REST APIs, JavaScript code, and JSON processing tools.

NDJSON Input to JSON Array Output

// NDJSON Input (each line is a separate JSON object)
{"id": 1, "event": "login",   "user": "alice", "ts": "2024-03-15T09:00:00Z"}
{"id": 2, "event": "view",    "user": "alice", "ts": "2024-03-15T09:01:32Z"}
{"id": 3, "event": "purchase","user": "bob",   "ts": "2024-03-15T09:04:11Z"}
{"id": 4, "event": "logout",  "user": "alice", "ts": "2024-03-15T09:07:55Z"}

// JSON Array Output (standard JSON, wraps all objects in [ ])
[
  {"id": 1, "event": "login",    "user": "alice", "ts": "2024-03-15T09:00:00Z"},
  {"id": 2, "event": "view",     "user": "alice", "ts": "2024-03-15T09:01:32Z"},
  {"id": 3, "event": "purchase", "user": "bob",   "ts": "2024-03-15T09:04:11Z"},
  {"id": 4, "event": "logout",   "user": "alice", "ts": "2024-03-15T09:07:55Z"}
]

Convert NDJSON to JSON in Code

// JavaScript / Node.js
const ndjsonToArray = (ndjson) =>
  ndjson.split('\n')
        .filter(line => line.trim())
        .map(line => JSON.parse(line));

// Python
import json
def ndjson_to_array(text):
    return [json.loads(line) for line in text.splitlines() if line.strip()]

// Bash (using jq)
jq -s '.' input.ndjson > output.json

// Command line (Node.js one-liner)
node -e "const d=require('fs').readFileSync('data.ndjson','utf8');
console.log(JSON.stringify(d.split('\n').filter(l=>l.trim()).map(JSON.parse),null,2));"

Convert JSON Array Back to NDJSON

// JavaScript
const arrayToNdjson = (arr) => arr.map(obj => JSON.stringify(obj)).join('\n');

// Python
def array_to_ndjson(arr):
    return '\n'.join(json.dumps(obj) for obj in arr)

// Bash (using jq)
jq -c '.[]' input.json > output.ndjson

NDJSON vs JSON: Key Differences

Choosing between NDJSON and a JSON array depends on how you plan to read, write, and process the data. Here is a detailed comparison of both formats: