The general appearance of the Boston Terrier should be that of a
lively, highly intelligent, smooth-coated, short-headed, compactly built,
short-tailed, well-balanced dog of medium station, of brindle colour and evenly marked with white.
The head should indicate a high degree of intelligence,
and should be in proportion to the size of the dog;
the body rather short and well knit, the limbs strong and neatly turned;
tail short; and no feature be so prominent that the dog appears badly proportioned.
The dog should convey an impression of determination, strength and activity,
with a style of a high order; carriage easy and graceful.
A proportionate combination of "colour" and "ideal markings"
is a particularly distinctive feature of a representative specimen,
and a dog with a preponderance of white on body, or without
the proper proportion of brindle and white on head, should possess sufficient merit
otherwise to counteract its deficiencies in these respects.

Not exceeding 25lb (11kg), divided by classes as follows:
lightweight, under 15lb (7kg); middleweight, 15lb. and under 20lb. (7-9 kg);
heavyweight, 20lb. and not exceeding 25lb. (9-11 kg).
Coat and Colour:

Coat short, smooth, bright and fine in texture.
Colour brindle with white markings. The brindle to be evenly distributed and distinct.
Black with white markings permissible but brindle with white markings preferred.
Ideal markings:

white muzzle, even white blaze over head, collar, breast,
part or whole of forelegs,and hind legs below hocks.
Faults:

Long or course coat; coat lacking lustre. All white; absence of white marking;
preponderance of white on body; without the proper proportion of brindle and white on head;
or any variation detracting from the general appearance.

Skull square, flat on top, free from wrinkles;
cheeks flat; brow abrupt, stop well defined.
Muzzle short, square, wide and deep,
and in proportion to skull;free from wrinkles; shorter in length than in width and depth,
not exceeding in length approximately one-third of length of skull;
width and depth carried out well to end; the muzzle from stop to end of nose
on a line parallel to the top of the skull.
Nose black and wide, with well-defined line between nostrils.
Mouth:

the jaws broad and square, with short regular teeth.
Bite even or sufficiently undershot to square muzzle.
The chops of good depth but not pendulous, completely covering the teeth when mouth is closed.
Eyes wide apart, large and round, dark in colour,
expression alert, but kind and intelligent.
The eyes should be set square in the skull, and the outside corners should be
on a line with the cheeks as viewed from the front.
Ears carried erect, either cropped to conform to the shape of the head,
or natural bat, situated as near the corner of skull as possible.
Faults:

Skull "domed" or inclined; furrowed by a medial line;
skull too long for breadth, or vice versa; stop too shallow;
brow and skull too slanting. Muzzle wedge-shaped or lacking depth;
down-faced; too much cut out below the eyes; pinched or wide nostrils;
butterfly nose; protruding teeth; weak lower jaw; showing turn-up,
lay back; wrinkled. Eyes small or sunken; too prominent;
light colour or walleye; showing too much white or haw.
Ears poorly carried or in size out of proportion to head.
Neck: Of fair length, slightly arched and carrying the head gracefully; setting neatly into shoulders.
Faults: Ewe-necked; throatiness; short and thick.
Forequarters: Shoulders sloping. Elbows standing neither in nor out.
Forelegs set moderately wide apart and on a line with the point of the
shoulders;
straight in bone and well muscled; pasterns short and strong.
Faults: Loose shoulders or elbows; long or weak pastern.