Disallow or replace certain characters in string with Firebase Realtime Database Security Rules?

Is it possible to disallow or replace certain characters in string with Firebase Realtime Database Security Rules?

For example disallow the "<" character?

Or replace the "<" with ">" character?

>Solution :

Yes, this is definitely possible with Firebase Realtime Database security rules.

You can use the .validate rule to specify a regex pattern that data must match. For your specific examples, you could do:

Disallow <: .validate(!newData.hasChildren() && !newData.val().matches('<'))
Replace < with >: .validate(!newData.hasChildren() && newData.val().replace('<', '>').matches('[your-regex-here]'))

The !newData.hasChildren() condition is included above to prevent the rule from being bypassed by writing nested data.