Être+adjective+?

Question

Is it a rule that être + adjective is always followed by the preposition de? Or can it be followed by à sometimes?

Accepted Answer

Danielle, 
à or de can follow ‘ être adjective ‘. 
The preposition used after the adjective in personal ‘ être adjective ‘ expressions depends on the adjective, not on the verb or noun following the adjective.  
In impersonal ‘ être adjective ‘ expressions, the subject ( ce or il ) being ‘ real ‘ or a ‘ dummy ‘ subject is the determiner of the preposition used.
For instance ‘ Prêt à manger ‘ are practically everywhere in France ! 
See link below to Laura Lawless site for discussion and lists : 
 https://www.lawlessfrench.com/grammar/adjectives-with-prepositions/
 https://www.lawlessfrench.com/grammar/using-impersonal-expressions/
 https://www.pretamanger.fr/fr-FR/shop-finder/l/paris