After having a radioactive spider bite him, inject its irradiated venom into his bloodstream, and give him its powers in the instant of its own death, Peter Benjamin Parker realized that he had, in effect, become a human spider--a Spider-Man.
He decided that a Spider-Man was nothing without a web, and thus he invented the wrist-worn devices he called his "web-shooters."
Initially meant to be tools of the professional stuntman's trade he had initially hoped to pursue, they have instead become his chief weapons as a crusading adventurer since after he came to believe that he could have prevented the murder of his uncle, Benjamin Parker, his reluctant abandonment of those professional ambitions in favor of the unpaid work of fighting crime, which he pursues on the principle that "with great power, there must also come--great responsibility."
The devices have remained the same throughout most of Spider-Man's career. When he was transformed and given organic web-shooters, Peter modified his mechanical web-shooters into bracelets for Mary Jane Watson to wear. However, that seems to have been retconned after the events of One More Day and Brand New Day. Ben Reilly donned modifications of them that he wore outside the wrists of the costume's gauntlets and allowed him to fire other web-like projectiles. Spider-Girl wears her own versions of the web-shooters.
One of the few modifications Spider-Man has made to the web-shooters is a red LED light, that will blink and let him know when he is about to run out of web fluid. Another upgrade is a small launcher on the back of the hand, which allows him to fire off his spider-tracers. In recent years, he has modified the shooters to fire on voice-command.
The Creation Of The Shooters, and Spider-Man's Webs
Spider-Man's web-shooters are twin devices, which he wears on his wrists beneath the gauntlets of his costume, that can shoot thin strands of a special "web fluid" (the chemical composition of which is not known, but which is described--see below--as being a "shear-thinning" substance) at high pressure. (Note: The fluid itself is officially described as being pressurized at 300 psi, but the actual number has been known to change.)
The spinneret mechanisms in each web-shooter are machined from stainless steel, except for the turbine component, which is machined out of a block of Teflon, and the two turbine bearings, which are made of amber and artificial sapphire. The wristlets and the web-fluid cartridges, the latter of which Spider-Man wears on his belt beneath his costume's tunic, are mainly nickel-plated annealed brass. The wristlets have sharp steel nipples, which pierce the bronze caps when the cartridges are tightly wedged into their positions.
The hand-wound solenoid-needle valve on each web-shooter is actuated by a palm switch; this, in turn, is protected by a band of spring steel which requires a 65-pound pressure to trigger it. The switch of each is situated high on Spider-Man's palm to avoid most unwanted firings. An additional safety measure, to prevent misfires while Spider-Man is making a fist or carrying things, is that the trigger has to receive a double-tap from Spider-Man's middle and third fingers. The small battery compartment is protected by a rubber seal.
The effect of the very small turbine pump vanes is to compress (shear) the web fluid and then force it, under pressure, through the spinneret holes, which cold-draws it (stretches it: the process wherein nylon gains a four-fold increase in tensile strength), then extrudes it through the air, where it solidifies.
As the web fluid exits the spinneret holes, it is attracted to itself electrostatically, and thus can form complex shapes. The spinneret holes have three sets of adjustable, staggered openings around the turbine which permit a single, incredibly strong line; a more complex, spreading spray; and a thick, tremendously adhesive liquid.
The web line's tensile strength has been estimated to be 120 pounds per square millimeter of the cross-section. The 300 p.s.i. pressure in each cartridge is sufficient to force a stream of the complex web pattern an estimated 60 feet. (It goes significantly farther if Spider-Man shoots it in a ballistic parabolic arc.)
Peter Parker devoted many hours of practice to weaving his webs in many different ways: as a shield, a parachute, a safety net, a barrier, skis, a raft, a club, a ball, or "plain, simple, sticky glue."
By weaving his webs into discs beneath his feet, he can walk across water  or fire. Given enough time, Spider-Man can even create sculptures out of his webbing, which will turn into a sticky mess on anyone who takes a swing at them.
One of Peter's problems with his web-shooters is getting them past metal detectors. At one point, he had to disassemble them and put the components amongst his camera equipment to get through airport security. As a result, he contemplated making them out of another material.
Web fluid is a shear-thinning liquid (virtually solid until a shearing force is applied to it, rendering it fluid) whose exact formula is unknown, but is related to nylon. On contact with air, the long-chain polymer knits and forms an extremely tough, flexible fiber with extraordinary adhesive properties.
The web fluid's adhesive quality diminishes rapidly with exposure to air. (Where it does not make such contact with air, such as at the attachment disk of the web-shooter, it remains very adhesive.) After approximately 1 hour, certain imbibed esters cause the solid form of the web fluid to dissolve into a powder.
At one time, Peter sought to sell the formula for webbing to make money, but the company to which he tried to sell it did not want it, not seeing the use for such a short-lasting glue. When Otto Octavius took over Peter's body, he modified the webbing to make it last far longer than Peter's and made it much stronger, to the extent that it became bullet-proof.
Peter would later learn of the improved webbing; after he had reclaimed his body, he was forced to make web underwear due to circumstances and, when it refused to dissolve after the usual hour, he was forced to wear pants instead of his costume's trousers until Anna Maria showed him where the new solvent was. 
Because the fluid almost instantly sublimates at its anaerobic liquid/solid phase transition point, there is no clogging of the web-shooter's parts.
Specialized Web Cartridges
- Ice Webbing was created specifically to combat the Human Torch. This webbing was able to hold him temporarily until he concentrated on burning at a higher temperature. Spider-Man subsequently discovered that his standard webbing was able to accomplish the same feat, though in a less flashy manner. Presumably, this is why he rarely used this variant.
- Acid Webbing was concocted after a string of murders led to William Baker, the Sandman. Peter concocted special webbing laced with hydrochloric acid, which could dissolve the individual granules of the Sandman's body. It proved successful in incapacitating him but not killing him, as Peter stated that he was not sure if anything could really kill him. Because the webbing looked the same as his original formula, Peter placed it into a green cartridge instead of the usual grey. He has also used this type of webbing as early as his initial encounters with the Rhino.
- Taser Webbing generates a bio-electric current within its semi-liquid substance; Spider-Man can use this to stun his opponents temporarily.
- Impact Webbing are Web-Pellets that, upon impact, release tendrils that ensnare the target. This variant was created by Benjamin Reilly, the Scarlet Spider.
- Magnetic Webbing is a variation of Spider-Man's original web-formula, with magnetized particles that will interfere with any remote-control frequencies.
- Lead-Lined Webbing is a variation of Spider-Man's original web-formula, with lead-like properties, allowing Spider-Man to contain radioactive materials safely.
- Flame Webbing is useful against Symbiotes. When Spider-Man fires it, his web-shooters eject a highly combustive chemical solvent from the ports, that will burst into flames upon contact with the intended target when entrapped in enough fluid. 
- Sonic Disruptors are useful against Symbiotes, and for the disruption of non-solid objects. When Spider-Man fires either, his web-shooters eject condensed sound frequencies in the direction of its intended target.
- Expanding Web-Foam is webbing that becomes foam once it comes out of the web-cartridge.
- Micro-Coiled Z-Metal are metallic-like strips that generate a bio-electric current, similar to that of a taser, to stun opponents temporarily. Peter has nicknamed this variant his "Bug Zappers."
- Quick-Drying Web-Cement dries instantly in contact with any surface and is capable of stabilizing weak structures. Also known as "Concrete Webbing."
Specialized Voice Commands
- Web Barrage automatically fires off multiple web bullets in rapid succession. If the words "full spread" are added, the range of the web bullets would increase.
- Wide Net instantly fires a large amount of webbing, in the shape of a net.
- Recoil Strand causes the webbing, and its intended target, to knock-back in the direction of the web-shooters.
Alternate Reality Versions
|On Earth-65, Janet Van Dyne gave Gwen Stacy (Spider-Woman) web-shooters that used moisture from the air to make an advanced web-fluid, which meant that as long as moisture was present, she never had to manually replenish the web-cartridges. She could form web lines, nets, and globs, along with more advanced shapes like web-wings and giant web-corn dogs.||Spider-Gwen (Vol. 2) #1|
|On Earth-1048, Peter Parker improved upon his Web-Shooters, making them more compact and able to hold more web-fluid.||Marvel's Spider-Man|
|On Earth-1610, Peter Parker successfully create a high pressure launching system to fire the adhesive "webbing" based on his father's incomplete formula for molecular adhesiveness. On his sixteen birthday, Tony Stark redesigned Peter's web-shooters as a gift. Peter's successor, Miles Morales was given Peter's web-shooters by Peter's Aunt May. A year later, Miles was given a new pair by Jessica Drew designed by S.H.I.E.L.D..||Ultimate Spider-Man #6|
|On Earth-8351, Peter Parker became an assassin working alongside Wolverine. He modified his web-shooters, allowing them to fire bullets and impact webbing.||What If? Spider-Man Vs. Wolverine #1|
|On Earth-9602, Spider-Boy was given a special pistol that fired strands of synthetic webbing.||Spider-Boy #1|
|On Earth-12041, Spider-Man is given the next Gen Web-Shooters by Nick Fury that was developed by Curt Conners, upon his recruitment into S.H.I.E.L.D thus replacing his first models Web-Shooters. These new Web-Shooters have a Holographic scope for aiming, a Camou-Mode to turn invisible as well as a Crossbow Mode. Not only do they shoot out enhanced webbing, but these also shoot Taser-Webs to stun foes and Flash-Webs to blind his enemies. The Web-Shooters have a button to create Web-Parachutes rather than having Peter making them himself.||Great Power|
|On Earth-20023, Sun-Spider fires webbing from her crutches.||Spider-Verse (Vol. 3) #6|
|On Earth-31411, Aaron Aikman secretly underwent a genetic treatment that imbued him with extraordinary powers. He then developed a suit, which had a built in silk-spinner with a cartridge full of silk solution. After a near-death battle with Naamurah he developed a stronger version for his silk solution.||Edge of Spider-Verse #3|
|On Earth-58163, George Stacy attempted to sell the shooters to the NYPD as a non-lethal protective weapon.||Spider-Man: House of M #1|
|In Earth-71928, Spider-Man modified his Web-Shooters to include a small caliber chain gun magazine. He utilized high armor piercing, EMP, explosives, and incendiary rounds. The sensors in his palms allowed for him to switch ammo types.||What If? The Punisher #1|
|On Earth-120703, Peter Parker used parts from two wrist watches and Oscorp spider silk technology, to successfully create a high pressure launching system to fire the adhesive "webbing". Two years later Peter upgraded his web-shooters.||The Amazing Spider-Man|
|On Earth-199999, the first model of web-shooters was created by Peter Parker. Later Tony Stark provided him with an even more advanced model along with a better costume(Spider-Man's Suit). The second model even had a Spider-Man's Spider-Signal.||Captain America: Civil War|
|On Earth-TRN604, Web-Slinger created his version of Web-pistol-like devices that were capable of shooting a special web fluid, this model resembles that of revolvers.||Return to the Spider-Verse, Part 2|
|On Earth-51838, Peter Parker created an updated version of his Web-Shooters using his resources at Parker Industries. This variant fired red webbing rather than the original grey.||Peter Parker: The Spectacular Spider-Man #301|
|On an Unknown Reality, a grown-up Spider-Man modified his Web-Shooters for a member of his technologically advanced police force member, Iron Spider.||Ultimate Spider-Man #200|
|On an Unknown Reality, Squirrel Girl created wrist bracelets that fired tree branches independently from Spider-Man.||Unbeatable Squirrel Girl #5|
- Web-Fluid was 2.62 times stronger than steel.
- The newest formula, created by Otto, keeps the web active until he activates a dissolving agent. However, the web also emitted trace radiation.
- Web-Fluid leaves an unpleasant odor.
- On Earth-1048, the fluid lasts for a few hours and can be removed with a mixture of baking soda, soap, and warm water.
- On Earth-12041, Web-Shooters (both artificial and organic) can be used to move about in the vacuum of space, as done by Spider-Man and Scarlet Spider.
- On Earth-13017, web-fluid becomes rancid if not used in a while.
- On Earth-26496, it has been said that web fluid adheres to fibrous substances, but also (jokingly) that it can be removed from human hair using ice or peanut butter.
- On Earth-199999, the chemicals for the formula of web fluid could be found in an average high school chemistry lab.
- On Earth-16220, the webbing loses adhesiveness if exposed to an electric current of about 100VDC.
- 4374 appearance(s) of Web-Shooters
- 301 minor appearance(s) of Web-Shooters
- 12 mentions of Web-Shooters
- 526 image(s) of Web-Shooters