JSONL Format Guide: Processing Large Datasets Line by Line

JSONL (JSON Lines) is a format where each line is a valid, independent JSON object. It's perfect for streaming large datasets, log files, and bulk API operations because you can process one object at a time without loading the entire dataset into memory.

JSONL Example

{"id": 1, "name": "Alice", "role": "engineer"}
{"id": 2, "name": "Bob", "role": "designer"}
{"id": 3, "name": "Charlie", "role": "manager"}

JSONL vs JSON Array

Real-World Use Cases

• Application logs (each event as a JSONL line)
• Database bulk imports/exports
• BigQuery and similar data warehouses
• Machine learning training datasets
• API bulk operations (OpenAI batch API, Stripe bulk requests)

Parsing JSONL

const lines = data.split("\n").filter(line => line.trim());
lines.forEach(line => {
  const obj = JSON.parse(line);
  // process one object at a time
  console.log(obj);
});