Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Scrappy and Determined
The story is told from a third-person perspective (check out the "Narrator Point of View" section for more on this), but it follows our scrappy protagonist Miri quite closely. Because of this, it's no wonder that some of Miri's spunk rubs off and infuses itself into the tone of the book.
When you read about Miri and her adventures, you see no wallowing or self-pity—instead it's all about sheer resourcefulness and making the best out of a situation. For example, when Tutor Olana tells Miri that she's being punished and will receive no more outside privileges, the book doesn't treat it as a tragedy:
"Yes, Tutor Olana." In truth, Miri did not mind. Between quarry-speech and Commerce, she had plenty to think about. (8.86)
The book is all about bouncing back and problem-solving—and that's not a bad attitude to take.