Learn German: Nein, es ist auch kein Schlüssel.

In German, we use kein (or keine) to negate nouns that usually take ein or eine (a/an). Since you would say "es ist ein Schlüssel" (it is a key), you negate it by simply changing ein to kein. You use nicht to negate verbs, adjectives, or nouns that have a definite article like der, die, or das.

Why is the ending just kein and not keine?

The ending of kein changes based on the gender of the noun. The word for key is masculine (der Schlüssel). Because it comes after the verb ist (is), it's in the basic subject case (Nominative). For masculine nouns in the Nominative case, the negative article has no extra ending, so it stays kein. If it were a feminine noun like die Lampe (the lamp), you would use keine.

Why does auch (also) come before kein?

In German, adverbs like auch generally sit right in front of the specific idea they are emphasizing or modifying. Here, the "also" applies directly to the fact that it is "not a key", so auch goes directly in front of kein Schlüssel.

Wait, if Schlüssel is masculine, shouldn't we use (he/it) instead of (it) to start the sentence?