What is a brownie in Spiderwick Chronicles?

Answer 1

Brownies are kind and dependable creatures that attatch themselves to human households where they help with chores, cleaning and protect the well-being of the people on "their" land.

Extremley loyal, brownies will defend a home and its surroundins from goblins and other bad creatures. They will like somewhere on the land they protect, perhaps in an abandoned barn/shed, an unused closet or within the roof or the walls of the house.

Despite their love of clenliness, Brownies are rather shabby in appearance, often going shoeless of often fully nacked. Even so, they expect no payment other than scraps of food and a bowl of milk left out at night. In fact, further gifts such as clothes and a small house, are likely to induce adverse effects.
Shuffling sounds and small squeaky voices heard at night is most likely a sign of a brownie. A careful observer may be able to spy on one at work is he or she can sneak up quietley enough. Even if not actually seen, the brownie may disappear in the middle of a task, leaving proof in the form of half-finished mopping or partually washed dishes.

Scattering flour on the floor is one way of obtaining footprints that may prove brownie activity. The problem with this method is that the brownie may simply clean up the mess.

Unusual organisation of items is also common in houses with brownies. A brownie may alphabetise books by the authors name or colour. Industrious themselves, even the gentlest of brownies hates laziness in others. If taken advantage of or otherwise ill-used, the brownie may become a boggart.

~ Athur Spiderwick's Field Guide

(P.S. Brownie's are actually real)

Answer 2

In the Spiderwick Chronicles, a brownie is a small fairy-like creature known for helping with household chores in exchange for small gifts. Brownies are depicted as mischievous but ultimately helpful beings in the series.