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_core::parser: Parsed 15 slides from markdown