What is a JSONL file?

JSONL (JSON Lines) is a file format where each line is a valid JSON object. It is commonly used for processing large datasets, logs, and AI training data because it can be processed stream-wise.

Yes, absolutely. This tool runs entirely in your browser (client-side). No files are ever uploaded to a server, ensuring your data remains private.

Can this tool remove duplicate entries?

Yes! The 'Smart Merge' feature automatically detects and removes duplicate JSON objects to ensure your dataset is clean.

Is there a file size limit?

Since processing happens in your browser, the limit depends on your device's available RAM. It can typically handle files up to several hundred megabytes smoothly.

JSONL Dataset Merger Online - Merge, Clean & Deduplicate JSON

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Drag & Drop JSONL files here

or click to browse (Max 500MB total recommended)

Merge Options Remove Duplicates (Deduplicate) Validate JSON (Skip invalid lines)

Output Format JSONL (Standard) JSON Array (Single file)

0 Total Lines Processed

0 Valid Lines Kept

0 Duplicates Removed

Preview (First 5 lines):

About JSONL Dataset Merger

The JSONL Dataset Merger is a powerful, free online tool designed for developers, data scientists, and AI researchers. It allows you to combine multiple JSONL (JSON Lines) files into a single, clean dataset. Unlike simple text mergers, this tool understands the JSON structure, enabling advanced features like deduplication and syntax validation.

Whether you are preparing training data for Large Language Models (LLMs) like GPT or Llama, aggregating log files, or managing large data exports, this tool ensures your final dataset is error-free and optimized.

How to Use

Upload Files: Drag and drop your `.jsonl`, `.json`, or `.txt` files into the upload area. You can select multiple files at once.
Configure Settings: Choose whether to remove duplicate entries (highly recommended for AI datasets) and validate JSON syntax to strip out corrupted lines.
Merge: Click the "Merge Files" button. The tool processes everything locally in your browser.
Download: Review the statistics and preview, then download your merged file or copy it to your clipboard.

Why Use This Tool?

Most command-line tools or simple text editors just append files together. This can lead to broken JSON syntax (e.g., missing newlines between files) or massive amounts of duplicate data. Our tool parses every line to ensure integrity.

Client-Side Privacy: Your data never leaves your computer. All processing happens in your browser's memory.
Smart Deduplication: We hash every JSON object to find and remove exact duplicates, saving you storage and training time.
Format Conversion: Easily convert a list of JSONL objects into a standard JSON Array file if needed.

Frequently Asked Questions (FAQ)

What is the difference between JSON and JSONL?

Standard JSON files contain a single object or array. JSONL (JSON Lines) contains one valid JSON object per line. JSONL is preferred for large datasets because it can be read line-by-line without loading the whole file into memory.

Can I merge huge files (1GB+)?

Because this tool runs in the browser, it is limited by your computer's RAM. It works best for datasets up to ~500MB. For multi-gigabyte files, we recommend using command-line tools like `jq` or Python scripts.

Does it work offline?

Yes! Once the page is loaded, you can disconnect from the internet and the tool will continue to function perfectly.

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