Then you want a safe incremental process that allows you to run unchecked code and annotate which code has been upgraded to meet the type checking standard - th

Then you want a safe incremental process that allows you to run unchecked code and annotate which code has been upgraded to meet the type checking standard - this is already done for javascript projects, you can introduce Flow to typecheck only the annotated functions in a file: https://flowtype.org/docs/existing.html https://flowtype.org/docs/existing.html