Carabiners are ovular, oblong, or pear-shaped metal clips with spring or locking screw gates. They are commonly used in mountain and rock climbing, repelling, sailing, tree climbing, fire and rescue, and industrial work like construction and window washing. There are several different types and grades of carabiners and rating standards for safety.

The American National Standards Institute (ANSI) sets standards for products in the United States while working in conjunction with international organizations. A carabiner used for life attachment should conform to ANSI standards. These carabiners will meet certain strength requirements and functionality, such as auto-locking and auto-closing.

Other ANSI safety requirements call for the carabiner to unlock only by two distinct actions, with a third action required to open it. Carabiners in this category must also meet a minimum strength requirement of 5,000 pounds (5 kilopounds). Many aluminum and steel carabiners meet these standards, though aluminum is favored for mountain climbing because it is lightweight.

Accessory carabiners used for rigging and similar purposes are not required to meet the ANSI standards for life support. Steel carabiners, generally stronger than aluminum, are often used when the weight of the carabiners themselves is not an issue.

Manufacturers usually stamp the breaking strength of a carabiner onto its side. This rating reflects the minimum force required to cause the carabiner to fail. Carabiners are tested in two ways: for vertical strength and for side-load, though generally carabiners are not intended to bear side-loads. Since the rating is based on force rather than weight, the numbers refer to kilonewtons instead of pounds or kilograms. A sufficiently accurate conversion to pound force can be obtained by multiplying kilonewtons by 225; giving a carabiner rated at 25 kilonewtons a 5,620 pound force rating, or 5.62 kilopounds.

Carabiners are light, strong, inexpensive, and handy —- even around the house, workshop, or office. Many people use carabiners for key rings or hammock rigging, or for hanging tools. They are also used for waterski lines, camping equipment, and a multitude of other applications. Carabiners are available from sporting goods shops, outfitters, marine and boating retailers, and recreational outlets of all kinds. Brightly colored carabiners are often displayed by the checkout registers of home improvement centers, though these are intended for simple uses that do not require safety considerations.