When it comes to tone, our narrator can be a straight shooter. He tells us what's what and who's who without any fuss. If you want to know what's going down without much commentary, this narrator is here to deliver. Check out this matter of fact description of the weather one day:
"The next day was rainy and dark. Rain fell on the roof of the barn and dripped steadily from the eaves. Rain fell in the barnyard and ran in crooked courses down into the lane where thistles and pigweed grew. Rain spattered against Mrs. Zuckerman's kitchen windows and came gushing out of the downspouts. Rain fell on the backs of the sheep as they grazed in the meadow. When the sheep tired of standing in the rain, they walked slowly up the lane into the fold." (4.1)
Here the tone is pretty objective. The narrator doesn't seem to feel particularly happy or sad about the rain; it just is. But we can't fully hop on the this-tone-is-objective-train because sometimes the narrator's opinion sneaks in. After all, the narrator has some choice words to say about Templeton's inherent evilness (go check out Templeton in "Characters" and then come back here).
Plus, during the sad moments of the book the matter of fact tone becomes more sympathetic. Take Charlotte's death, for instance:
"The Fair Grounds were soon deserted. The sheds and buildings were empty and forlorn. The infield was littered with bottles and trash. Nobody, of the hundreds of people that had visited the Fair, knew that a grey spider had played the most important part of all. No one was with her when she died." (21.52)
The tone here is still pretty straightforward, giving us the details of Charlotte's death. But the tone also asks us to sympathize with poor lonely spider. She was important, and, because we're all nice people (right, Shmoopers?), we don't want an important and kind spider like Charlotte to die.