JSONLines

JSONLines, also known as JSON Lines, JSONL, or NDJSON (Newline Delimited JSON), is a simple, newline-delimited text format for storing multiple JSON values. In a JSONLines file, each line is a complete JSON value—typically an object—separated by newline characters. The file is usually UTF-8 encoded, and lines can be added or read sequentially without loading the entire dataset into memory. Because each line is independent, a parser can stream through the file and process one record at a time. Within a line, strings must escape newlines, so a line break does not split a record.

Usage and applications: JSONLines is commonly used for log files, data ingestion pipelines, streaming ETL, and real-time analytics. It supports append-only workflows and efficient incremental processing, since processing can begin at the start or at any line boundary. Many languages provide straightforward line-oriented readers that emit one JSON value per line.

Limitations: JSONLines does not enforce a schema or group records into a single payload like a JSON array, making some cross-record constraints harder to express. A malformed line can disrupt a processor, so robust pipelines include per-line error handling and validation. Some tools expect single-line objects for compatibility, though values other than objects are permitted.

See also: NDJSON, JSON, line-delimited data formats.