The Alpha Jet is a light twin-engine aircraft equipped with an intentionally simple airframe despite the performance delivered. Both the leading edges and air intakes are fixed; while the aerodynamic shape of the aircraft, which was developed with the aid of computer aided design (CAD), conforms with the area rule. Fully powered controls are used, comprising a dual-hydraulic systems and load-factor limited dynamic feel system arrangement attached to conventional flight control surfaces. The cockpit is pressurised for greater comfort during training. The Alpha Jet is designed to accommodate ten-minute turn around times with minimal ground equipment, using features such as pressurised single-point refueling, ladder-less entering/egress of the cockpit, and a ten-hour endurance of the liquid oxygen system.

The Alpha Jet was designed to perform a diverse range of roles. The principal users of the type, Germany and France, operated their Alpha Jets in different capacities, the former as a ground attack platform and the latter as a trainer aircraft. Beyond performing different roles, the Alpha Jet fleets of France and Germany noticeably differed in their specification and equipment; German aircraft were fitted with a more extensive weapon-aiming system, a different fuel system, a yaw damper, different brakes, nosewheel steering, an arrester hook, and Stencel ejector seats in place of Martin-Baker. According to aerospace publication Flight International, the majority of the specialised equipment used on the ground attack-orientated variant of the Alpha Jet was provided by German firms. In addition to the ground attack role, the Luftwaffe also employed the Alpha Jet in the electronic countermeasures (ECM) and aerial reconnaissance roles; for the latter purpose, a reconnaissance pod could be fitted upon the port hardpoint.

The Alpha Jet is powered by a pair of SNECMA Turbomeca Larzac turbofan engines. It is a low bypass-ratio, twin-spool engine that uses modular construction methods. The Larzac was a new engine at the time, having only performed its first run a year prior to being selected to power the Alpha Jet. The need for greater thrust to power the aircraft than the original model of the engine could generate led to the development and adoption of the 2,970 lb Larzac 04 in February 1972; it was this version of the engine that initially powered the Alpha Jet. Germany was interested in powering the type with the General Electric J85, but France objected to the use of an American engine which would result in US export restrictions upon the overall aircraft and agreed to assume the cost of developing the French-built Larzac. During the 1980s, an upgraded model of the Larzac engine which increased the thrust by 10 per cent was developed.

The avionics of the original version of the Alpha Jet were of an austere nature, partly to make it a simple and easily exportable aircraft. The basic type lacked features such as an autopilot, inertial navigation, or a radar. Later upgrade programs would typically focus on the addition of a glass cockpit and other avionics systems. The Luftwaffe's Alpha Jets were equipped with additional avionics for the attack role, such as a Doppler radar and additional hardpoints. During the 1970s, Dornier claimed that the Alpha Jet outperformed aircraft used as the McDonnell Douglas F-4 Phantom II, LTV A-7 Corsair II, and Fairchild Republic A-10 Thunderbolt II in the close air support role; the firms specifically stated that the Alpha Jet was smaller, faster, less vulnerable, more maneuverable, cheaper and had higher all-round performance than the A-10.

According to aerospace publication Flight International, the Alpha Jet was more complex than competing second generation trainer aircraft, required seven man hours of maintenance for every flight hour. Nearly 5,000lb of munitions and equipment may be carried upon a total of five hardpoints, four of these being located upon the wings and a single one at the centerline on the lower fuselage. In an armed configuration, a gun pod containing a 30 mm DEFA cannon (as installed on French aircraft) or 27 mm Mauser BK-27 cannon (as installed on German aircraft) would typically be installed upon the centerline hard point.