NDJSON validator (JSON Lines)
Validate NDJSON and JSON Lines files line by line, see which lines have errors and the most common fields, and convert to a JSON array.
How to useValidate NDJSON.
Fields found
Available in: 
NDJSON validator (JSON Lines): what it is for
Paste or open an .ndjson or .jsonl file and the tool validates it line by line, showing how many lines are fine, which ones have errors (with line number and reason) and how many are blank. It also lists the fields found and in what percentage of lines each appears, and converts everything to a JSON array you can download.
Everything runs in your browser: nothing you paste or open is sent to a server.
How to use
- Paste the content or open the file.
- See the lines with errors.
- Download as a JSON array if you want.
When to use it
- Check database exports and logs.
- Prepare batch files for APIs.
- Find the line that breaks an import.
Frequently asked questions
What is NDJSON?
It is a format where each line is a complete, independent JSON (newline-delimited JSON, also called JSON Lines or .jsonl). It is widely used in logs, database exports and batch APIs such as BigQuery and OpenAI.
Are blank lines an error?
No. Empty lines are ignored and counted as blank.
Does my data leave the browser?
No. Validation runs entirely in your browser, even with large files.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 are free.