Frequently asked questions
Is my file or data uploaded?
No. The file is read and validated entirely in your browser. Nothing you paste or open is sent anywhere or stored.
What does it check?
It reads each line as a separate JSON value, counts how many are valid, and lists the exact line numbers and error messages for any that are not, which is the usual cause of a fine-tuning or eval upload failing.
What are the top-level keys for?
For the valid records it shows which top-level keys appear and how often, so you can quickly spot records missing an expected field, such as a missing role or content key.
Can it handle large files?
It validates every line and shows the full counts, and to stay fast it displays the first 300 records in the expandable list while still reporting totals and all errors.
Why is one line flagged but it looks fine?
JSONL needs each line to be a complete JSON value on its own. A trailing comma, a missing brace or quote, or a record split across two lines will fail, and the error message points to what went wrong.