JSONL
Newline-delimited JSON — one JSON object per line, used for streaming logs, datasets, and LLM batch input.
Definition
JSON Lines (also called NDJSON) puts one JSON object per line, no enclosing array. It streams easily, appends safely, and reads line-by-line without parsing the whole file. JSONL is the standard format for log aggregation, LLM fine-tuning datasets, Anthropic and OpenAI Batch API input, and Claude Code's session transcripts.