Professional JSONL Tools

Free Online JSONL Viewer & Editor

Gigabytes. Local first.

View and edit JSONL files up to 1GB instantly in your browser. A free JSONL file reader with streaming, syntax highlighting, and real-time validation. No uploads, no sign-up — your data stays on your device.

Drop a file, paste text, or type JSONL

Supports .jsonl, .ndjson, .json, .txt

What is JSONL?

JSONL (JSON Lines) is a lightweight text format where each line is a standalone JSON object separated by newlines. It is the go-to format for streaming large datasets, application logs, and machine learning pipelines — used extensively by OpenAI, Hugging Face, and major cloud platforms.

Unlike a single JSON array, JSONL files can be read and written one line at a time, making them ideal for processing gigabytes of data without loading everything into memory. Learn more about JSONL format →

Whether you're reviewing OpenAI fine-tuning datasets, inspecting Hugging Face training data, or debugging application logs, jsonl.co gives you a fast, private JSONL dataset viewer that works with files of any size.

Why jsonl.co?

Handle Gigabyte Files

Open and view large JSONL files up to 1GB+ directly in your browser. No crashes, no freezing — a streaming JSONL file reader that handles datasets other tools can't.

100% Private & Secure

All processing happens locally in your browser. Your JSONL data never leaves your device.

Free Forever

No sign-up, no limits, no hidden fees. A completely free online JSONL viewer and editor — open JSONL files without installing anything.

Full JSONL Format Support

A complete JSONL viewer, NDJSON viewer, JSON Lines parser and editor with built-in JSONL validator and syntax highlighting. Supports .jsonl, .ndjson, and .json files.

Side-by-Side View

Raw JSONL on the left, parsed JSON on the right. Edit and preview in real time with synchronized scrolling.

Multi-Language Support

Available in multiple languages. The same powerful JSONL tool, localized for developers worldwide.

More JSONL Tools

JSONL to JSON Converter

Convert JSONL files to JSON format instantly. Free, fast, and private.

JSON to JSONL Converter

Convert JSON arrays to JSONL format. Process large files with streaming.

JSONL to CSV Converter

Export JSONL data to CSV spreadsheets. Handle millions of rows effortlessly.

JSONL Formatter

Format and beautify JSONL files with configurable indentation and key sorting.

JSON vs JSONL Guide

Learn the differences between JSON and JSONL formats, and when to use each.

Frequently Asked Questions

How large of a JSONL file can I open?
jsonl.co can handle JSONL files up to 1GB and beyond. We use streaming technology to read your file in chunks, so it loads instantly without consuming all your memory. Only the visible portion is rendered at any time.
Is my data sent to any server?
No. All processing happens 100% locally in your browser. Your JSONL data never leaves your device — no uploads, no server-side processing. This makes jsonl.co safe for sensitive and proprietary data.
What is JSONL format?
JSONL (JSON Lines) is a text format where each line is a valid JSON object, separated by newlines. It’s widely used for streaming data, log files, and machine learning datasets. Unlike JSON arrays, JSONL files can be processed line by line without loading the entire file into memory. Read our full guide on JSONL format →
What’s the difference between JSON and JSONL?
JSON stores data as a single object or array, while JSONL stores one JSON object per line. JSONL is better for large datasets and streaming because each line can be parsed independently. See the detailed JSON vs JSONL comparison →
What file formats are supported?
jsonl.co supports .jsonl, .ndjson (Newline Delimited JSON), .json, and .txt files. All formats are parsed line by line as JSONL content.
Can I edit JSONL files?
Yes. For smaller files, you can directly edit the raw JSONL text in the left panel. Changes are parsed and validated in real time on the right panel. You can also add new lines, delete lines, and use find & replace. When you’re done, export the edited file with one click.
Can I use jsonl.co as an NDJSON viewer?
Yes. jsonl.co fully supports NDJSON (Newline Delimited JSON), which follows the same one-object-per-line format as JSONL. Simply open your .ndjson file and it will be parsed and displayed just like any JSONL file.
Can I view OpenAI fine-tuning JSONL files?
Yes. jsonl.co is ideal for viewing and editing OpenAI fine-tuning datasets in JSONL format. You can inspect prompt-completion pairs, validate each line's structure, and export corrected files — all without uploading your training data to any server.
JSONL Viewer & Editor Online — Open Large JSONL Files (No...