One of the integral hallmarks of the French Bulldog is its Silhouette & Topline, after its Square Head & Bat Ears. An ideal Frenchie should always be cobby, compact and shapely, maintaining that desired curvy topline especially on the move.
I personally prefer to judge the topline on the move as a dog can hunch to exaggerate, or over-stretch to ‘flatten’ its topline. Clever coiffing/sculpting can also help create the illusion of a topline, but the real topline is an actual curvature of the spine.
The correct topline should start after the withers, with the highest point above the middle of loin, followed by a round croup and finished with a low-set tail. The position and degree of the roach are important criteria to consider when assessing topline. The topline should blend in cohesively with the rest of the silhouette for a perfect seamless finish. If the topline is the first thing you notice on a Frenchie, it is most likely over-exaggerated, wrongly-positioned and incorrect.

Too many are misinterpreting an exaggerated wheel-back, and high-in-the-rear as the proper acceptable toplines when in actuality, they are major serious structural faults to be avoided, and very difficult to eliminate in a breeding program. Especially the latter, if we are truly evaluating breeding stock to improve spinal health and overall conformation of the breed.
A more prominent topline does not make it a better topline, as this is a moderate breed that calls for no single feature to be in excess nor lacking. All parts should fit together perfectly (without in excess) for that balanced desired outline that’s distinctly and authentically French Bulldog.
Article by Diane Burvee, French Bulldog Breed Expert & Judge