ContextActionService is a game service that allows a game to bind user input to contextual actions, or actions that are only enabled under some condition or period of time. For example, allowing a player to open a door only while close by. In code, an action is simply a string (the name of the action) used by the service to differentiate between unique actions. The action string is provided to ContextActionService/BindAction|BindAction and ContextActionService/UnbindAction|UnbindAction, among other member functions. If two actions are bound to the same input, the most recently bound will take priority. When the most recent action is unbound, the one bound before that takes control again. Since ContextActionService deals with user input, you can only use it in LocalScript|LocalScripts which run on the client.

What is a context?

A context is simply a condition during which a player may perform some action. Some examples include holding a Tool, being Seat|seated in a car or standing near a door. Whatever the case may be, it is up to your LocalScript|LocalScripts to call BindAction when the context is entered and UnbindAction when the context is left.

What is an action?

An action is simply some input that can be performed by the player while in that context. Such an action could open/close some menu, trigger a secondary tool action or send a request to the server using RemoteFunction/InvokeServer. An action is identified by a unique string as the first parameter of both ContextActionService/BindAction|BindAction and ContextActionService/UnbindAction|UnbindAction. The string can be anything, but it should reflect the action being performed, not the input being used. For example, don’t use “KeyH” as an action name - use “CarHorn” instead. It is best to define your actions as a constant at the top of your script since you will use it in at least three different places in your code.

Why bind actions contextually?

It’s better to use ContextActionService’s ContextActionService/BindAction|BindAction than UserInputService/InputBegan for most cases. For InputBegan, your connected function would have to check if the player is in the context of the action begin performed. In most cases, this is harder than just calling a function when a context is entered/left. For example, if you want to have the H key trigger a car horn sound while the player is sitting in it, the player might type “hello” in chat or otherwise use the H key for something else. It is harder to determine if something else is using the H key (like chat) - the car might honk when the player didn’t mean to! If you instead use ContextActionService/BindAction|BindAction and ContextActionService/UnbindAction|UnbindAction when the player enters/leaves the car, ContextActionService will make sure that H key presses trigger the honk action only when it is the most recently bound action. If something else (like chat) takes control, you won’t have to worry about checking that.

Inspecting Bound Actions

To see a list of actions and their bound inputs, you can inspect the “Action Bindings” tab in the Developer Console (F9 while in game). This shows all bindings - including those bound by Roblox CoreScripts and default camera/control scripts too. This is useful for debugging: check if your actions are being bound/unbound at the correct times, or if some other action is stealing input from your actions. For example, if you are attempting to bind WASD, it may be the case that default character movement scripts are binding over those same keys. Similarly, the camera control script can steal right-click input if the script runs after yours.

Keyboardless Input

ContextActionService is especially useful for supporting gamepad and touch input. For gamepad input, you might choose to bind the B button to an action that returns the user to the previous menu when they entire another menu. For touch, on-screen touch buttons can be used in place of key presses: these buttons display only while the action is bound, and the position, text and/or images of these buttons can be configured through this service. They are somewhat limited in the amount of customization provided by this service; it’s usually a better idea to make your own on-screen buttons using ImageButton or TextButton.