First off, check this site for examples of explanations of tone and mood in "The Necklace." I've given links below.
The tone of the story is the author's attitude toward his subject. In this story, de Maupassant is detached from his characters, but the reader never gets the feeling he doesn't care about them. When Monsieur and Madame Loisel find that the borrowed necklace is lost the author shows us the fear and apprehension of his characters and we truly feel their shock:
They looked at each other aghast. Finally Loisel got dressed again.
“I’ll retrace our steps on foot,” he said, “to see if I can find it.”
And he went out. She remained in her evening clothes, without the strength to go to bed, slumped in a chair in the unheated room, her mind a blank. Her husband came in about seven o’clock. He had had no luck. He went to the police station, to the newspapers to post a reward, to the cab companies, everywhere the slightest hope drove him. That evening Loisel returned, pale, his face lined; still he had learned nothing.
We feel bad for the couple but, to their credit, they never sink into despair. They stick to their plan and eventually pay off the expensive necklace. Later de Maupassant even has admiration for Madame Loisel as she goes from being dissatisfied and bored to resourceful and hard working:
Mme. Loisel experienced the horrible life the needy live. She played her part, however, with sudden heroism. That frightful debt had to be paid. She would pay it. She dismissed her maid; they rented a garret under the eaves.
The mood is the way a writer wants the reader to feel about the story and characters. There are a few moods apparent in this story. In the beginning we may feel disdain for Madame Loisel because she is never satisfied. After all, she has a loving husband who is thoughtful enough to get invitations to a fancy ball and buy her a new dress. She also is privileged enough to have a maid.
When Madame Loisel loses the necklace we feel the same shock as her and her husband, and, after they are unable to locate it, we may feel despair. While Madame Loisel is working off the debt we actually feel good for her. She finally has a purpose in life and she is no longer bored and envious.
The story is full of interesting imagery. We can picture the life of the wealthy and privileged as Madame Loisel daydreams about what it would be like to live the life of the rich:
She would dream of silent chambers, draped with Oriental tapestries and lighted by tall bronze floor lamps, and of two handsome butlers in knee breeches, who, drowsy from the heavy warmth cast by the central stove, dozed in large overstuffed armchairs.
Likewise, the description of the ball paints a picture of a wealthy social gathering. We are also given a portrait of the beautiful Madame Loisel as she dances the night away.
We are presented with a picture of Paris at night as the couple leave the ball:
They walked toward the Seine, disconsolate and shivering. Finally on the docks they found one of those carriages that one sees in Paris only after nightfall, as if they were ashamed to show their drabness during daylight hours.
Finally, de Maupassant paints a picture of what day to day life for the poor would have been like in 19th century France. He describes the work Madame Loisel has to do to pay off "The Necklace":
She learned to do the heavy housework, to perform the hateful duties of cooking. She washed dishes, wearing down her shell-pink nails scouring the grease from pots and pans; she scrubbed dirty linen, shirts, and cleaning rags which she hung on a line to dry; she took the garbage down to the street each morning and brought up water, stopping on each landing to get her breath. And, clad like a peasant woman, basket on arm, guarding sou by sou her scanty allowance, she bargained with the fruit dealers, the grocer, the butcher, and was insulted by them.
"The Necklace," as presented in its English translation, is without metaphors and similes.
There are several symbols in the story. Of course, the chief symbol is the necklace, which represents wealth, class and status. It's ironic that this symbol of wealth ends up being made of paste, a sly slap at upper class France. Other symbols of wealth and status include the material objects Madame Loisel describes in the opening section and the fancy ball she attends. Symbols of Madame Loisel's mundane life include the soup tureen her and her husband eat from, and the theatre dress her husband suggests she wear to the ball.
The satire in the story is tied up with the irony. Although the necklace is much sought after by Madame Loisel, and for her represents everything she is missing out on in life, it ends up being false. The Loisels go deep into debt for something that is basically worthless. The author may be saying that the wealthy, such as Madame Forestier, are really fake. Madame Loisel admires Forestier, but in the end, the wealth of Madame Loisel's friend is without merit.
Foreshadowing includes hints and clues that may alert the reader to what may happen next in a story. De Maupassant provides no foreshadowing in this story, probably because he wants us to be totally shocked at the end when the necklace is revealed to be a fake.