Log Formatter
Parse and display NDJSON / JSON Lines log files. Auto-detects level, timestamp, message, and service fields with color-coded severity.
Parses NDJSON (Newline Delimited JSON). Auto-detects level, msg, time, and service fields. Click a row to expand all fields.
About this tool
Structured logging stores log entries as machine-readable data — typically JSON — rather than unstructured text strings. This approach allows log aggregation platforms (Elasticsearch, Datadog, Grafana Loki, Splunk, AWS CloudWatch) to efficiently filter, search, and alert on specific fields across millions of log entries from distributed services. NDJSON (Newline Delimited JSON), also called JSON Lines, is the standard format: one JSON object per line.
Log levels form a severity hierarchy used to control verbosity. TRACE and DEBUG provide detailed diagnostic information useful during development. INFO records normal operation events — service started, request received, task completed. WARN flags potentially problematic conditions that do not prevent normal operation. ERROR records failures that affect a specific operation. FATAL or CRITICAL indicates a failure severe enough to stop the application. In production environments, typically only INFO and above are collected to control log volume and cost.
Popular structured logging libraries that produce NDJSON output include Pino and Bunyan for Node.js, zerolog and zap for Go, and structlog for Python. Each has different default field names for the standard fields — timestamp may appear as time, ts, or @timestamp; the message as msg or message; the level as level, lvl, or severity. This tool automatically detects common field name conventions to provide a consistent display regardless of which library produced the logs.