From the UK Breed Standard
Small, powerful, sturdily built, alert energetic worker.
Works cattle but has terrier instincts when rabbiting and ratting.
Courageous, happy, affectionate to owner.
Head and Skull
In proportion to body. Skull flat and wide between ears, tapering towards eyes which are set wide apart. Moderate stop equidistant between nose and occiput. Tapering continues towards nose. Skull and muzzle to be parallel planes.
Almond-shaped, medium size, dark color except in liver where they may be lighter to match coat color.
Showing alert lift, or erect. Drop ears showing no lift undesirable.
Lips firm. Scissor bite – jaws strong with a perfect, regular and complete scissor bite, i.e. upper teeth closely overlapping lower teeth and Set Square to the jaws. Under or overshot to be discouraged.
Moderate length, well laid into shoulders.
Well laid shoulder, elbows firm against ribs. Amply boned. Pasterns allow feet to turn slightly outwards, but not enough to cause weakness or affect freedom of movement.
Well sprung ribbing, extending well back with close coupling. Firm, level topline, never dipping at withers or falling at croup. Approximately 1 inch longer than height at withers. (Measured from withers to set on of tail)
Muscular, with well-turned stifles, hocks well let down. From rear should be parallel, when moving or standing. Never bandy or cow hocked.
Small, firm and well padded.
Set on high, left natural. Carried over back in a slight curve when alert, but not forming a complete ring.
Smart and brisk. Natural, free movement.
Fine undercoat is covered throughout by weather resistant, short, thick, hard, flat topcoat. Topcoat slightly longer on neck. Undercoat should not show through topcoat nor allow any longer hair at the mane to stand off. Long or excessively wavy coat highly undesirable.
Black or liver with tan marking on muzzle, spots on cheeks and often above eyes, from knees downwards, with desirable thumb-mark above feet, inside handles and under tail. Richness of tan may fade with age. White to be discouraged, except for a very small spot on fore chest being permitted, but not desired. Pigmentation to tone with coat color.
Ideal height at shoulder: dogs-12 inches, bitches-10 inches.
Any departure from the foregoing points should be considered a fault and the seriousness with which the fault should be regarded should be in exact proportion to its degree and its effect upon the health and welfare of the dog.
Note: Male animals should have two apparently normal testicles fully descended into the scrotum.