logplain

Logplain is a term used in discussions of log formatting to describe a lightweight, human-friendly plain-text logging approach. It is not a formal standard but a concept that emphasizes readability, simplicity, and portability across tools and platforms. In a logplain approach, each log entry is a single line containing a timestamp, a severity level, a source or component, and a human-readable message. Many implementations also attach structured key=value data after the main message to enable lightweight parsing without breaking readability.

Typical line format: ts=2025-12-09T12:34:56Z level=INFO src=auth msg="User login successful" user=alice

Another example: ts=2025-12-09T12:35:02Z level=ERROR src=db msg="Connection failed" code=ECONNREFUSED

Logplain favors tools that can filter and search plain text logs with standard Unix utilities, as well as simple log rotation and compression. Compared with JSON-based formats, logplain entries are generally easier for humans to skim in terminal windows but offer less rigorous structure for automated parsing at scale. It can be used in small services, development environments, or situations where minimal tooling is available.

Origin and status: the term arose in informal discussions among developers and system operators as a way to describe a readable fallback to more complex structured formats. It is not an official standard, and practitioners may customize field names and conventions to suit their workflows.

See also: plain-text logging, structured logging, JSON Lines, syslog.