Validate JSON Lines Files Instantly
JSON Lines (JSONL) and NDJSON are the standard formats for storing one JSON object per line, and they power many modern AI and machine learning workloads — from fine-tuning datasets and embeddings pipelines to streaming logs and LLM training corpora. A single malformed record can break a downstream parser, so validating every line before you feed a file into a job matters.
Find Invalid Records Fast
Paste a JSONL file (or load one from disk) and the validator parses each line independently. Any line that is not valid JSON is reported with its exact line number, a descriptive error message and a short snippet, so you can jump straight to the problem without scrolling through thousands of lines.
Spot Silent Data Issues
Beyond hard errors, the tool flags minor warnings such as whitespace-only lines and lines with leading or trailing whitespace. These usually do not break parsing but can cause inconsistencies when files are diffed, hashed or concatenated across tools.
Configurable Empty-Line Handling
Empty lines are common in hand-edited datasets. With "Ignore empty lines" enabled (the default), blank lines are skipped silently; turn it off to surface every whitespace-only line as a warning so you can clean the file completely.
Private, Fast and Offline-Ready
All validation runs client-side using your browser's own JavaScript engine. Your dataset is never uploaded, which makes the tool safe for proprietary or sensitive training data, and everything recalculates instantly as you type.