File tools
Browser-side file portability and inspection tools — "will this look the same everywhere, and why?"
Markdown Portability Preflight
Finds Markdown constructs that render differently across GFM, CommonMark and stripped-down renderers.
EML/MIME Import Doctor
Checks a raw .eml file for constructs that behave differently across mail clients and importers.
Text File Portability Preflight
Checks a plain text file for encoding/line-ending/whitespace issues that behave differently across operating systems, editors and tools.
MIME Attachment Filename Doctor
Checks attachment filenames declared inside a raw .eml/MIME message for portability problems when saved to disk across Windows, macOS and Linux.