Term
JSONL
JSON Lines — a file format where each line is a self-contained JSON object. Used universally for LLM training data, evaluation sets, and batch inference inputs. One example per line, no top-level array, easy to stream.
Background
OpenAI, Anthropic, and Hugging Face all use JSONL as the training-data interchange format. The format streams cleanly (line-by-line read), tolerates partial corruption (one bad line, rest still parses), and avoids the giant-array problem that breaks on naive JSON parsers. Conventional file extension is .jsonl or .ndjson (newline-delimited JSON).