The GWT editor runs validations on translations as they are typed, and immediately displays problems detected by the validators.
The React editor should be able to run any of the standard validators, based on the settings for the project-version (off/warning/error).
List of validators (taken from GWT editor validation options):
Leading/trailing newline (\n)
Positional printf (XSI extension)
Tab characters (\t)
XML entity reference
Integrate Validators with alpha editor Validation component
Apply Validators selected as Warning / Error in validation option settings