The Gekko model is comprised of a mechanical "head" and body, each separate and connect by a small mechanical joint, joined to long legs and clawed feet composed of artificially created muscle tissue derived from the embryonic stem cells of ungulate embryos. A 360-degree sight is mounted on top of the machine with another between the legs, both equipped with advanced sensors and imaging devices. They mount some form of propulsion system and are capable of leaping great distances into the air, either to travel quickly or to crush enemy soldiers.
They are also extremely flexible and agile, capable of maneuvering through small corridors and rooms originally designed for humans that would otherwise be inaccessible; Gekko legs use universal ball joints, allowing them a large range of motion. Sometimes, it shuts most of its operating systems to the extent that it can easily be mistaken for having its drive go dead to the naked eye, which also acts as a surprise attack for an unwary traveler.
A Gekko mounts a whip-like manipulator arm ending in a small claw-like gripper, which it can use to pick up delicate objects for examination or manipulate objects; the grip is strong enough to restrain a grown adult. Occasionally when faced with a hidden enemy, a Gekko will produce a hand grenade using the manipulator and throw it.
After combat maneuvers, the Gekko are seen to excrete an amount of luminous green fluid. This is most likely lactic acid built up from the activity of their organic parts. They are completely autonomous, sporting an artificial intelligence that is capable enough to chase a target through multiple levels of a building and recognize and investigate signs of a target's presence; however, this A.I. is not perfect, giving them roughly animal intelligence; they are seen to misjudge the ability of structures to support their weight at times, and are easily deceived by a wily opponent. Gekko are deployed in huge numbers; in some national militaries, they outnumber tanks, though are clearly not designed to fulfill the same role. Gekko can only see heat. The Gekko are often transported via trucks, and despite the size of the Gekkos, they are surprisingly light when compacted.
Gekko communicate in sounds modeled after animals, mooing and bellowing like cows and sometimes chirping like cicadas.
The standard Gekko variant is highly modular, capable of mounting a number of weapons in various combinations on its "head"; all mount a machine gun in an internal station near the 'beak' of the head, and typically additional armament will be some combination of tube-launched anti-tank missiles, M2 Browning .50 caliber heavy machine guns and grenade discharging arrays, though a handful mount electronic warfare devices that can deflect incoming guided missiles. It is unclear how these weapons are restocked, though the Gekko has no obvious capacity for reloading its own weapons in the field; presumably they must withdraw once the fixed armament is depleted, though in the context of the game they have infinite ammunition.
There is also a "Suicide" variant, appearing to be a stripped-down Gekko frame with a nuclear demolition charge located in the head area.
The Dwarf Gekko (also known as Scarabs) are spheres with a single optical unit that have three small arms with human looking hands attached to the end. They can give off a shock that appears to be emitted from the optical unit. A shock from this can throw people off balance. Gekko are also seen carrying groups of Dwarf Gekko on the back of their "heads".
Gekko are heavily armored and highly agile, capable of making great leaps, swift sprints and climbing vertical walls. They are capable of attacking with their legs, their whip-like manipulation arms and whatever mounted weaponry they have, which typically consists of at least one machine gun housed in the "nose", and may also include machine guns on the shoulders and anti-tank missiles. Some examples also mount a white electronic warfare device on one of the shoulder hardpoints; this is capable of spoofing incoming missiles, sending them off-course or detonating them prematurely.
Be wary when hiding from a Gekko, as if it is aware of Your approximate location, after a while it will produce a hand grenade with its manipulator tentacle and throw it.
Gekko are vulnerable to immobilization following damage to their legs; one leg damaged will immobilize the Gekko but still allow it to pivot its head to fire, while both will render it completely helpless temporarily. The actual vulnerable point on a Gekko is on the top of its head near the sensor unit; shots to this area with any weapon will damage it. Anti-tank missiles and RPGs will damage a Gekko regardless of aim, though if not immobilized it may dodge them.
It is extremely easy to destroy a Gekko with a railgun, as the projectile typically travels too quickly for them to dodge, and a single fully charged shot to any part of the head will kill a Gekko instantly. It is also possible to tranquilize a Gekko. It takes about four to five shots on the front of the legs and one to two in the back of the knee of the Gekko using the tranquilizer gun. It's best to take caution when combating a Gekko because even though it's machine guns will not kill you instantly, a kick from the Gekko's legs can. It would be best if you have a recovery item (Like a medical kit) equipped when encountering a Gekko. Be aware that the Gekko have magnets attached to them. These magnets will repel any Rocket projectiles shot at them.
While the Gekko tend to not use nuclear weapons, Otacon implies that some might have nuclear capability when he says "not all of them have nuclear capability" when stating that they have different types of Gekko for different missions.