Why can't I pretty-print and keep valid JSONL?

Strict JSONL needs exactly one object per line, so pretty-printed output is for reading and reviewing. Use minify mode to produce a file you can feed back to a tool.

How does deduplication work?

Records are compared by canonical JSON with keys sorted, so objects that differ only in key order count as duplicates.

What happens to invalid lines?

By default they're dropped and counted. Turn off 'Drop invalid' to keep them verbatim so you can fix them manually.

Does sorting keys change my data?

No — only the key order changes, which makes git diffs and dataset comparisons far easier to read.

Is my data uploaded to a server?

No. This tool runs entirely in your browser using standard web APIs, so your input never leaves your device and nothing is logged or stored on our servers.

JSONL Formatter

Pretty-print, minify, sort and deduplicate JSON Lines files.

Support

Works Offline

Privacy First

No Login

No API

JSONL input

Mode

Indent

Sort keys

Drop invalid

Deduplicate

Line comments

Drop a file here

Drop a .jsonl or .ndjson file

Formatted output

Records

Kept

Invalid

Duplicates

JSON

{
  "id": 1,
  "role": "user",
  "content": "hello"
}

{
  "id": 2,
  "role": "assistant",
  "content": "hi"
}

About the JSONL Formatter

Make JSONL readable or make it strict. Expand each record for review, minify back to one-object-per-line, sort keys for stable diffs, drop invalid lines and remove duplicate records before training or importing.

Examples

Minify

JSON{
  "id": 1
}

Output

JSON{"id":1}

Keyboard shortcuts

Copy the main outputCtrl / ⌘ + Shift + C
Download the resultCtrl / ⌘ + S
Share this toolCtrl / ⌘ + Shift + S
Reset the inputsAlt + R
Open the tool search paletteCtrl / ⌘ + K

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Frequently asked questions

Version 1.0.0 · Updated 2026-08-14 · Runs entirely in your browser