Adults have black legs and a small thin dark bill. The body is dark brown on top and mainly white underneath, with brown streaks on the breast and a white rump. They have a white stripe over their eyes. This bird shows long wings in flight. In winter plumage, this species is pale gray above. This bird can be difficult to distinguish from other similar tiny shorebirds; these are known collectively as "peeps" or "stints".
One of the best identification features is the long wings, which extend beyond the tail when the bird is on the ground. Only the Baird's Sandpiper also shows this, and that bird can be distinguished by the lack of a white rump.
These birds forage by probing on mudflats or tundra or picking up food by sight in shallow water. They mainly eat insects, mollusks and marine worms, also some plant material.
Hybrids between this species and the Dunlin are occasionally found in northeastern North America (McLaughlin & Wormington, 2000, and external link below); the White-rumped Sandpiper is also suspected to hybridize with the Buff-breasted Sandpiper.