Layman's version:
Up to 20 hens (no roosters over 4 months old) confined in a clean coop.
 The Urban Chicken ordinance on the books:
Link to municipal code online: Code Enforcement
 Code Enforcement
A. Under no circumstances shall the animals and fowl mentioned above be permitted to run at large or to suffer or permit such animals and fowl to habitually create noise so as to continuously disturb the peace of another citizen. They shall be kept confined at all times in a suitable enclosure, coop, cage, stable, barn or shed, with enclosed runway. Such enclosure shall be of sufficient size to safely and adequately house, maintain and exercise the animal and fowl, and provide adequate shelter from the elements and other animals.
B. Such house, coop, cage, stable, barn, shed or runway shall at all times be maintained in a clean and sanitary condition; shall be cleaned one a week or more often if necessary; and shall at all times be free from offensive odors.
C. Every such house, coop, cage, stable, barn, shed or enclosed runway shall at all times be kept in such condition as to comply with all sanitary rules and regulations of the City and County Health Department.
D. On any property housing more than five (5) or more adult animals, no part of any such house, coop, cage, stable, barn, shed or runway for such animals or fowl shall be placed within the required front, side or rear setbacks as delineated in the City Zoning Ordinance.
E. No more that twenty (20) adult animals shall be permitted within the City.
F. No rooster over four (4) months old shall be permitted within the City.
H. It shall be unlawful and a public nuisance to keep any animal or fowl for commercial purposes.
The Belmont Answer Book "A Resident's Guide to Frequently Asked Questions" (last published in 2008) states that a permit is required though the Code Enforcement page does not (emphasis added):
"Does Belmont allow me to keep chickens, horses, or goats?
You may keep domestic fowl, such as chicken, goose, duck, turkey, pigeon, dove, and squab. You must apply for a special permit from animal control services, and all such animals must be confined in a coop or shed at all times. Also, the coop or shed must be 20 feet from all streets, all lot lines, and all dwellings. No rooster over four months old is permitted."