Code cracker for feminine and masculine french words?

There is no rule to guess if a French Word is masculine of feminine, unless you find it in a sentence.

The articles for masculine Words are "le" and "un", for feminine nouns they are "la" and "une"

le soleil (the sun), un avion (a plane): masculine nouns

la lune (the moon), la table (the table): feminine nouns

Of course it will be difficult to tell when for liaison purposes, the is a "l" and apostrophe before the noun ("l'idée"). Try to change the "l" for "un" or "une" (une idée = an idea, feminie noun)

It may also be difficult when the nouns are in plural form (les soleils, les lunes).

the form of any adjective next to the noun may help.

"il a une allure masculine" (he has a masculine appearance) "allure" is feminine, because it uses the feminine article "une", and because the adjective "masculine" is the feminine form of the adjective "masculin"

"elle a un air féminin" (she has a feminine apperance): "féminin" is the masculine form of the adjective, and the Word "un" indicates that "air" is masculine.

Adjectives often end with an "e" when in feminine form.

masc. bruyant, fem. bruyante (noisy)

masc. perdu, fem. perdue (lost)