Logging

Lantern uses the tracing framework for internal logging and diagnostics. By default, logging is disabled, but can be enabled via environment variables for debugging and troubleshooting.

Configuration

File Path

To enable logging to a file, set the LANTERN_LOG_FILE environment variable:

export LANTERN_LOG_FILE=/path/to/lantern.log
lantern present slides.md

If LANTERN_LOG_FILE is not set, logs are discarded and won't appear anywhere.

Level

Control the verbosity of logs using the --log-level flag:

LANTERN_LOG_FILE=debug.log lantern --log-level debug present slides.md

Usage Examples

Basic Debugging

Enable info-level logging for general troubleshooting:

LANTERN_LOG_FILE=lantern.log lantern present slides.md

Detailed Diagnostics

Enable trace-level logging for in-depth debugging:

LANTERN_LOG_FILE=lantern-trace.log lantern --log-level trace present slides.md

Temporary Log File

Use a temporary file that gets cleaned up automatically:

LANTERN_LOG_FILE=/tmp/lantern-$$.log lantern present slides.md

Log Format

Logs are written in plain text format without ANSI color codes, making them easy to read and process with standard tools:

2025-11-18T10:30:45.123Z INFO lantern_cli: Presenting slides from: slides.md
2025-11-18T10:30:45.234Z INFO lantern_cli: Theme selection: CLI arg=None, frontmatter=oxocarbon-dark, final=oxocarbon-dark
2025-11-18T10:30:45.345Z DEBUG lantern_cli::parser: Parsed 15 slides from markdown