Miraculous tools, also known as Miraculous weapons, are special omni-purpose tools that come with their respective Miraculouses. Whenever a Miraculous owner transforms, they possess a tool specific to whichever Miraculous they're wearing.
For the sake of seeing and communicating with kwamis, a mage in ancient times created the Miraculouses, magic jewels. At the same time of making them, the mage created tools to go with each one.
Since each tool was used by different people throughout time and history it's not uncommon for them to change in their appearances like the staff of the Cat Miraculous. When being used by Hei Mao the weapon appeared to be made out of bamboo or another type of wood. While being used by Cat Noir it appears to be made out of metal.
Besides their Miraculous weapons, some wielders also can fight with additional weapons like Tentomushi with her nekode, La Coccinelle with her rapier, and Ladybug with Kagami's saber in "Riposte". Some weapons can split apart like Cat Noir's staff, showing that they are capable of dual-wielding.
When utilizing Unification, Miraculous holders can dual-wield both weapons, such as when Dragon Bug fought with both the dragon sword and the ladybug yo-yo.
Each tool is a different object, like Ladybug's yo-yo and Cat Noir's staff. These tools come in a great variety of different forms, including toys, musical instruments, and actual weapons. Usually, the tool is a size that can easily be carried by hand, and most tools can be worn when they aren't in use, such as Ladybug wrapping her yo-yo around her hips or Cat Noir having his staff attached to his back.
Sometimes, when fusion powers are used, Miraculous tools can change color, like how the mouse jump rope changed from pink to orange, red and black upon the Mouse Miraculous being fused with the Fox, Ladybug, and Cat Miraculouses, respectively. Also, the tool's appearance can change according to its user, as the Turtle Miraculous' shield has a different form when used by Carapace and Jade Turtle.
As when using a Miraculous transformation power up form, Miraculous tools can also change their appearance, such as when Ladybug changed into her ice form the spots on the yo-yo changed into hexagons.
The tools are used as weapons, being incredibly handy for both offense and defense. The tools are indestructible; the only thing that can break them is the powerful magic of a miraculous, such as the Butterfly Miraculous power in Simon Says' command card, or the force of a Miraculous owner's superstrength.
Some tools are capable of being used as a mode of transportation. An example of this is when Ladybug uses her yo-yo to swing from place to place, while Cat Noir can vault himself with his staff.
The tools also have technological features, including a phone, a camera, a GPS, and a search engine, among a number of other features.  The features of the Miraculous tools "update" in accordance with the technologies of the time.
It has been shown that the tools can be used as a breathing device underwater.
The tools also have detachable features, such as tracking devices and ear communicators. The tools also have storage capabilities which are connected to the users non-super method of storage (ex. when the miraculous owner stores something in their purse, the item is relocated to the tool upon transformation). The same rule applies to pictures taken using a tools camera function. When the Miraculous owner is detransformed, the photographs will transfer to their regular phone.
Sometimes under certain conditions, the tools can be used by regular people and other miraculous holders if the owner becomes separated from them such as Ladybug using Cat Noir's staff seen in several episodes, with Nino using the staff in "Anansi" and Alix in using Ladybug's yo-yo in "Reverser".
For some Miraculous owners, they need the tool to use their special superpower. For example, the Ladybug Miraculous owner tosses the yo-yo into the air when utilizing the Lucky Charm, the Fox Miraculous owner plays the flute to cast Mirage, the Turtle Miraculous owner holds up the shield to engage Shell-ter, the Bee Miraculous owner spins the spinning top and catches it to use Venom, and the Peacock Miraculous holder plucks feathers from the hand fan to Amokization. However, when the tools are used to summon their superpowers, the owners can't use them to attack or defend themselves (except for weapons that aren't used to summon their powers, Cataclysm and Akumatization, etc). If they are attacked during the process, the powers will be canceled out. If an owner becomes separated from their weapon, they can't summon their powers.
A Miraculous owner can call their weapon back to them from afar, though this has only been displayed by an owner who already has their adult powers. Some younger Miraculous owners have displayed the ability to mentally control their tools, so it could be possible that the connection strengthens upon adulthood. However, if the weapon is destroyed, then the mental connection will be broken leaving the holder unable to call them back.
When the Miraculouses are used in fusion, the weapon of one Miraculous can be combined with the superpower of the other jewel, creating a new effect. Like as Dragon Bug, Ladybug combined the powers of the Water Dragon and her yo-yo causing the shield making ability to expand to not only protect her but Cat Noir as well as protecting them from the titular villain's wasps. But to what other effects the weapons could have when under the power fusion is unknown.
When Théo Barbot and Chloé Bourgeois get akumatized into copies of Cat Noir and Ladybug respectively, they possess identical versions of the original superheroes' tools with the same features.
Lila Rossi's akumatization into a replica of a Fox Miraculous holder includes her possessing a copy of the flute.
The real flute in "Sapotis" has the same abilities as Volpina's flute, but Rena Rouge's flute can only create one illusion as opposed to Volpina's many illusions. After the flute has been used once, the Fox Miraculous starts to time out when a teen is using, but for an adult, & Volpina's Miraculous replica doesn't.
As depicted in art in "Ladybug & Cat Noir", Herakles had a spear and Tomoe Gozen had a naginata, although it's uncertain if these weapons are the tools to their unknown Miraculouses or additional weapons.
In "Reverser", "Queen Wasp", and "Mayura" it is revealed that the Miraculous tools can be used for breathing underwater, even if Cat Noir and Ladybug are not in aqua form.
Miraculous tools can also be destroyed by Cataclysm as seen in "Mayura".
Also hinted in "Mayura", Ladybug wanted to used Hawk Moth's cane to track him implying that Miraculous tools can be used to find their owners when lost, although Hawk Moth detransforms before they can.
In "Oblivio", it's revealed that the weapons when converted into their phone forms have a user's guide.
In "Miracle Queen", the tools can also be turned into akumatized and amokitized objects.
However, for amokization, if the owner detransforms, the Sentimonster gets destroyed because the object is gone.
With Cat Noir's staff, Rena's flute, Carapace's shield, Viperion's lyre, Pegasus' horseshoe, Ryuko's sword, King Monkey's ruyi jingu bang and Bunnyx's umbrella, their weapons are attached to their backs and yet the tools are never seen falling off. It implies that their suits are covered in a special adhesive or due to the magical properties of suit that allow the objects to stay attached.
It's implied while under the power of fusion or when Miraculous holder gets older, their weapons will have other features or the power to fuse together.