JSONL Formatter — Line-by-Line Validator
Format, validate, and inspect JSON Lines (JSONL) and NDJSON files. Validates each line individually, reports parse errors by line number, outputs compact JSONL or a pretty-print preview, and lets you download the cleaned file.
How to Use JSONL Formatter — Line-by-Line Validator
How to Use the JSONL / NDJSON Formatter
What is JSONL / NDJSON?
JSON Lines (JSONL) and Newline Delimited JSON (NDJSON) are text formats where each line is a self-contained, valid JSON value — most commonly a JSON object. They are widely used for:
- Log streaming and aggregation (Datadog, Loki, CloudWatch)
- BigQuery and Snowflake data imports
- Large dataset exports and ETL pipelines
- Streaming API responses
- Machine learning training datasets
Example valid JSONL:
{"id":1,"name":"Alice","role":"admin"}
{"id":2,"name":"Bob","role":"user"}
{"id":3,"name":"Carol","role":"viewer"}
Step 1: Paste Your JSONL
Paste your JSONL or NDJSON content into the input box. Each line should contain exactly one JSON object or value. Empty lines are allowed and are counted separately from errors.
Step 2: Check the Stats
The tool immediately reports:
- Total Lines — total line count including empty lines
- Valid JSON — lines that parsed successfully
- Errors — lines that failed to parse (invalid JSON)
- Empty Lines — blank lines (ignored in output)
Step 3: Review Errors
If any lines fail to parse, the Parse Errors panel shows:
- Line number
- The exact parse error message
- A preview of the problematic line content
Common errors:
- Unquoted keys:
{name: "Alice"}→ must be{"name": "Alice"} - Trailing commas:
{"a":1,}→ not valid JSON - Single quotes:
{'name': 'Alice'}→ must use double quotes - Truncated lines: JSON cut off mid-object
Step 4: Choose Output Mode
- Compact JSONL (default) — reformats each valid line as minified single-line JSON. This is the standard NDJSON format, ready for file imports and pipeline processing.
- Pretty Preview — formats each object with 2-space indentation, separated by blank lines. This is for human reading only and is not valid NDJSON — do not use this output in pipelines.
Step 5: Copy or Download
- Copy JSONL — copies the compact output to clipboard
- Download .jsonl — downloads the compact JSONL output as
output.jsonl, containing only valid lines
The downloaded file strips all empty lines and reformats each object as compact JSON. Invalid lines are excluded from the output.
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