Work with JSONL files of any size, in your browser
Open multi-GB files, fix bad lines, convert formats, and sort out LLM batch results and agent logs. Your files never leave your computer.
Open a JSONL file Validate a file
Tools
- JSONL ViewerOpen JSONL files of any size, jump to any line and search them.
- JSONL ValidatorFind bad lines, with fixes, and check OpenAI and Anthropic formats.
- Batch Results AnalyzerMatch OpenAI and Anthropic batch results to requests and build a retry file.
- Agent Log ViewerRead Claude Code and Codex session logs as a conversation.
- JSONL to CSV ConverterFlatten JSONL into a CSV file for spreadsheets.
- CSV to JSONL ConverterTurn CSV rows into JSONL records without mangling IDs.
- JSONL to JSON ConverterWrap JSONL records into a single JSON array.
- JSON to JSONL ConverterTurn a JSON array or pretty-printed objects into JSONL.
- JSONL SplitterSplit a file by lines or size, with presets for provider batch limits.
- JSONL MergerCombine several JSONL files into one.
Why your files stay private
JSONL files often hold training data, customer records or agent logs. Every tool here processes files locally. Pages are also served with a Content-Security-Policy of connect-src 'none', which makes the browser block fetch, XHR, WebSocket and beacon requests from the page, and you can check that header in your browser’s developer tools. Read exactly what is and isn’t collected.
Guides
- What is JSONL?The format, its rules, and when to use it.
- JSONL vs JSONHow they differ and how to choose.
- JSONL vs NDJSONWhether the two names mean different things.
- How to fix common JSONL errorsWhat each error means and how to fix it.
- How to open large JSONL filesOptions for multi-GB files, in the browser and on the command line.
- OpenAI Batch API JSONL formatInput, output and error files, with limits.
- Anthropic Message Batches results formatResult types, custom_id rules and limits.
- Where Claude Code stores session logsLocation, structure and how to read them.
- Browser JSONL benchmarkMeasured indexing and search speed on a 5 GiB file.