Free data conversion tool
CSV to JSON Lines (JSONL) converter
Turn a CSV or TSV file into one JSON record per line (JSONL / NDJSON). Your data is processed 100% locally in your browser and is never uploaded for conversion.
1. Add your data
Paste delimited text or choose a local file. Commas, tabs, semicolons, and pipes are detected automatically.
Blank lines are skipped. Editing this text after choosing a file changes what gets converted.
Off by default. With this option off, every cell stays a string.
2. Review and export
The preview, clipboard, and downloaded .jsonl file contain the same text.
Renamed columns
What is JSON Lines (JSONL / NDJSON)?
JSON Lines (also referred to as JSONL or Newline Delimited JSON / NDJSON) is a structured text data format where every single line is an independent, valid JSON object or array. Unlike standard JSON documents that wrap data in a outer array [...], JSON Lines separates records using simple newline characters (\n).
This format is heavily used in large-scale data engineering, machine learning pipelines, LLM fine-tuning datasets, log aggregation platforms (such as Elasticsearch and Datadog), and streaming database exports because each record can be parsed individually without needing to hold the full dataset in memory.
How JSON Lines conversion works
Each input data row becomes a compact, valid JSON value on its own line. In object mode, the first CSV row supplies property names. Repeated names get suffixes such as _1 and _2; blank names become empty_field_1, empty_field_2, and so on.
The converter stops if a data row has a different number of cells from the header. Fix the CSV and convert again to avoid losing data.
CSV vs. Standard JSON vs. JSON Lines
| Feature / Metric | CSV (Comma Separated) | Standard JSON | JSON Lines (.jsonl / NDJSON) |
|---|---|---|---|
| Record Separator | Newline (\n) |
Comma inside Array | Newline (\n) |
| Streaming & Large Files | Moderate | Poor (Must parse full JSON) | Excellent (Line-by-line reading) |
| Nested Data Structures | Not Supported | Full Support | Full Support (Per line) |
| Primary Use Cases | Spreadsheets, Tabular Exports | Web APIs, Configuration | LLM Datasets, Logs, Big Data |
Example CSV to JSON Lines Conversion
Input CSV / TSV
name,age,role,active
Ada Lovelace,36,Mathematician,true
Grace Hopper,85,Computer Scientist,falseOutput JSON Lines (.jsonl)
{"name":"Ada Lovelace","age":36,"role":"Mathematician","active":true}
{"name":"Grace Hopper","age":85,"role":"Computer Scientist","active":false}Frequently Asked Questions
Is my CSV data kept private and secure?
Yes. All parsing and conversion is executed entirely client-side inside your browser using the Papa Parse JavaScript library. Your data never leaves your device and is never transmitted to any external server.
What delimiters does this converter support?
The converter automatically detects commas (,), tabs (TSV), semicolons (;), and pipe symbols (|).
How does the tool handle missing or duplicate header columns?
In Object mode, empty header cells are assigned explicit names like empty_field_1. Duplicate header names receive incremental numeric suffixes (e.g. column_1, column_2) to ensure all object keys are preserved without overwriting data.
Is there a file size limit for CSV uploads?
Because processing takes place locally in your browser's memory, file size is limited only by your computer's RAM. Tens of thousands of rows convert cleanly in seconds.