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Logging Configuration

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VSTO Add-in (C#)

• Framework – Uses NLog (vsto-addin\NLog.config).
• Default Targets
  • File: %LOCALAPPDATA%\X21\Logs\X21.log
  • Optional console target when debugging via Visual Studio.
• Log Levels – Controlled via appsettings.json under Logging.LogLevel. Production typically runs at Info, while development can use Debug.
• Custom Events – Key services (Excel API, TaskPane manager, PostHog service) log detailed messages about API calls, selection changes, and errors.

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Deno Orchestrator

• Framework – Custom rotating file handler built atop the Deno standard log module (src/utils/logger.ts).
• Directory – %LOCALAPPDATA%\X21\X21-deno\Logs.
• Rotation Strategy – Writes to deno-<machine>.log for the current day and archives previous days as deno-<machine>_YYYY-MM-DD.log.
• Configuration
  • DENO_ENV=development enables DEBUG level logging.
  • DENO_LOG_COLORS=false disables colour codes when piping logs.
  • DENO_CONSOLE_LOGS=false writes only to file (useful in production).

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Langfuse Tracing

• Captures high-level metadata: prompt, user email, workbook, tool spans, compacting events, and user feedback.
• Accessible via the Langfuse dashboard; configure API keys as described in API Configuration.
• Use traces to correlate user reports with exact tool executions.

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Viewing Logs

• Excel API logs—Open the folder displayed in the CLI or use the Windows Run dialog: %LOCALAPPDATA%\X21\Logs.
• Deno logs—Navigate to %LOCALAPPDATA%\X21\X21-deno\Logs. Files are plain text and easy to parse.
• ClickOnce publish logs—publish\publish.log records output from Publish.ps1.

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Best Practices

• Rotate or archive logs periodically to avoid disk bloat, especially on shared workstations.
• Mask sensitive data before sharing logs. Tool payloads can include workbook values or formulas.
• Align log levels across components—running the backend in DEBUG while the add-in is at INFO can make correlation difficult.
• Consider feeding logs into a central monitoring solution if you operate X21 at scale (e.g., ship to Azure Log Analytics or Splunk).