German Strong Adjective Endings

In English and in German, adjectives can be placed before nouns or after nouns. In German, if an adjective is placed before the noun, it takes specific endings depending on the case and gender of the noun. If an adjective is placed before the noun, and is preceded by an “ein”-word (indefinite article, negative artice, possessive article: ein, kein, mein, etc), then it has “strong” endings. 

Example:
Eine Tomate ist rot.    A tomato is red.  
The adjective “red” is placed behind the noun “Tomate”, so the adjective has no endings, and stays the same for any noun regardless of gender. However:

Eine reife Tomate ist rot.    A ripe tomato is red. 
The adjective “reif” is placed before the noun “Tomate” so it has an ending. Because we used the indefinite article “eine”, the ending is considered “stong”. 

In the above example, “Eine reife Tomate ist rot.”, the noun “Tomate” is feminine and in the nominative case, so the strong adjective ending is “-e” (reife)

Examples:
Mein Auto ist schnell.  My car ist fast.
The adjective “schnell” is behind the noun “fast”, so it has no ending. 

Mein schnelles Auto war teuer.  My fast car was expensive. 
“schnell” is before the nominative neutral noun “Auto” so it has the ending “-es” 

Ihre Haare sind lang.  Her hair is long (lit. Her hairs are long.) 
“lang” is behind “Haare”, so no ending is needed. 

Ihre langen Haare sind blond. Her long hair is blond.
“lang” is before the nominative, plural noun “Hair” so it has the ending “-en”.