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Logs

This page provides information about Langflow logs, including logs for individual flows and the Langflow application itself.

Langflow uses the loguru library for logging.

The default logfile is named langflow.log. Langflow also produces logfiles for flows.

Log storage​

The default logfile storage location depends on your operating system:

  • macOS Desktop:/Users/<username>/.langflow/cache
  • Windows Desktop:C:\Users\<username>\AppData\Roaming\com.Langflow\cache
  • OSS macOS/Windows/Linux/WSL (uv pip install): <path_to_venv>/lib/python3.12/site-packages/langflow/cache
  • OSS macOS/Windows/Linux/WSL (git clone): <path_to_clone>/src/backend/base/langflow/cache

To customize log storage, see Configure log options.

Configure log options​

Use Langflow environment variables to configure logging options in your Langflow .env file, and then start Langflow with uv run langflow run --env-file .env.

The following environment variables are available to configure logging:

  • LANGFLOW_LOG_LEVEL: Sets the log level as one of DEBUG, ERROR (default), INFO, WARNING, and CRITICAL. For example, LANGFLOW_LOG_LEVEL=DEBUG.

  • LANGFLOW_LOG_FILE: Sets the log file storage location if you want to use a non-default location. For example, LANGFLOW_LOG_FILE=path/to/logfile.log.

  • LANGFLOW_LOG_ENV: Controls log output and formatting.

    • LANGFLOW_LOG_ENV=container: Outputs serialized JSON to stdout.
    • LANGFLOW_LOG_ENV=container_csv: Outputs CSV-formatted plain text to stdout.
    • LANGFLOW_LOG_ENV=default or unset: Outputs prettified output with RichHandler.

  • LANGFLOW_LOG_ROTATION controls when the log file is rotated, either based on time or file size. By default, logs are rotated every 1 day.

    • Time-based rotation: "1 day", "12 hours", "1 week"
    • Size-based rotation: "10 MB", "1 GB"
    • Disable rotation: "None" (log files will grow without limit)

A complete example .env file is available in the Langflow repository.

Flow and component logs​

After you run a flow, you can inspect the logs for the each component and flow run. For example, you can inspect Message objects ingested and generated by Input and Output components.

View flow logs​

In the visual editor, click Logs to view logs for the entire flow:

Logs pane

Then, click the cells in the inputs and outputs columns to inspect the Message objects. For example, the following Message data could be the output from a Chat Input component:


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"messages": [
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{
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"message": "What's the recommended way to install Docker on Mac M1?",
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"sender": "User",
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"sender_name": "User",
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"session_id": "Session Apr 21, 17:37:04",
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"stream_url": null,
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"component_id": "ChatInput-4WKag",
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"files": [],
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"type": "text"
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}
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],

In the case of Input/Output components, the original input might not be structured as a Message object. For example, a Language Model component might pass a raw text response to a Chat Output component that is then transformed into a Message object.

You can find .log files for flows at your Langflow installation's log storage location. For filepaths, see Log storage.

View chat logs​

In the Playground, you can inspect the chat history for each chat session. For more information, see View chat history.

View output from a single component​

When debugging issues with the format or content of a flow's output, it can help to inspect each component's output to determine where data is being lost or malformed.

To view the output produced by a single component during the most recent run, click Inspect output on the component in the visual editor.

See also​

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