What it checks
Whether the JSON is a routine the app reads: the form it says it is in, the keys and words the schema names, a time written as a time. What it cannot check is anything about your phone: whether a shortcut by that name exists there, or a place, or a date you named.
A link opens the routine on an iPhone with Routine Run, where nothing is saved until you press Add. Links carry form 1 until the version of the app that reads form 2 is on the App Store. Form 2 is the same routine in the app's own words, with its own schema; the app reads both.
The same checks run from a terminal, with the package in the public repository: routinerun check, routinerun link, and routinerun new to start from one of the routines the app ships.