All user-facing strings must be documented with translation function usage to ensure proper internationalization support. This includes error messages, notifications, labels, and any text displayed to users. Example: ```typescript // ❌ Don't use hardcoded user-facing strings const notice = `Image file is too large (${imageSizeInMB} MB). The maximum allowed size is 5 MB.` // ✅ Document translation key usage for user-facing strings const notice = t('tools:readFile.imageTooLarge', { size: imageSizeInMB, max: 5 }) ``` Key requirements: - Use translation keys in a hierarchical format (e.g., 'category:subcategory.messageId') - Document parameter interpolation when variables are used - Include translation key usage in code comments and documentation - Mark strings as user-facing in documentation when applicable This ensures maintainable internationalization support and clear documentation of translatable content throughout the codebase.