Adjectives in Spanish will always “agree” with the noun in “number and in gender.”
In other words, if the noun is masculine and singular, the adjective will be masculine and singular.
Also, the adjective generally follows the noun in Spanish. The phrase – “the handsome boy” is “el muchacho guapo.” The phrase “the handsome boys” changes to “los muchachos guapos.”
An example with a feminine adjective, “the beautiful island” – “la isla bonita.”
Students delight in hearing that “el pollo loco” is actually grammatically correct!