Cloud functions


Expose a function through the Cloud so that it can be called with POST /v1/devices/{DEVICE_ID}/{FUNCTION}.

Particle.function allows code on the device to be run when requested from the cloud API. You typically do this when you want to control something on your device, say a LCD display or a buzzer, or control features in your firmware from the cloud.

bool success = Particle.function("funcKey", funcName);

// Cloud functions must return int and take one String
int funcName(String extra) {
  return 0;

Each function call request and response uses one Data Operation from your monthly or yearly quota. Setting up function calls does not use Data Operations.

Up to 15 cloud functions may be registered and each function name is limited to a maximum of 12 characters (prior to 0.8.0), 64 characters (since 0.8.0).

Note: Only use letters, numbers, underscores and dashes in function names. Spaces and special characters may be escaped by different tools and libraries causing unexpected results. A function callback procedure needs to return as quickly as possible otherwise the cloud call will timeout.

The callback function is called application loop thread context, between calls to loop(), during Particle.process(), and delay().

In order to register a cloud function, the user provides the funcKey, which is the string name used to make a POST request and a funcName, which is the actual name of the function that gets called in your app. The cloud function has to return an integer; -1 is commonly used for a failed function call.

A cloud function is set up to take one argument of the String datatype. The argument has a maximum size of 64 to 1024 bytes of UTF-8 characters; see API Field Limits as the limit varies depending on Device OS version and sometimes the device.

Functions can only be triggered using the Particle API, or tools that use the API, like the console, CLI, and mobile apps. It's not possible to directly call a function from another device, even on the same account. Publish and subscribe can be used if you need device-to-device communication.

For non-product devices, only the account that has claimed the device can call a function on it.

For product devices, if the device is claimed, the device owner's account can call a function on it. Additionally, the product owner can call a function whether the device is claimed or not.

When using the default AUTOMATIC system mode, the cloud functions must be registered in the setup() function. The information about registered functions will be sent to the cloud when the setup() function has finished its execution. In the SEMI_AUTOMATIC and MANUAL system modes, the functions must be registered before Particle.connect() is called.

Before 1.5.0: Variable and function registrations are only sent up once, about 30 seconds after connecting to the cloud. When using the AUTOMATIC system mode, make sure you register your cloud functions as early as possible in the setup() function, before you do any lengthy operations, delays, or things like waiting for a key press. Calling Particle.function() after the registration information has been sent does not re-send the request and the function will not work.


int brewCoffee(String command);

void setup()
  // register the cloud function
  Particle.function("brew", brewCoffee);

void loop()
  // this loops forever

// this function automagically gets called upon a matching POST request
int brewCoffee(String command)
  // look for the matching argument "coffee" <-- max of 64 characters long
  if(command == "coffee")
    // some example functions you might have
    return 1;
  else return -1;

You can expose a method on a C++ object to the Cloud.


class CoffeeMaker {
    CoffeeMaker() {

    void setup() {
      // You should not call Particle.function from the constructor 
      // of an object that will be declared as a global variable.
      Particle.function("brew", &CoffeeMaker::brew, this);

    int brew(String command) {
      // do stuff
      return 1;

CoffeeMaker myCoffeeMaker;

void setup() {

The API request will be routed to the device and will run your brew function. The response will have a return_value key containing the integer returned by brew.


curl \
     -d access_token=123412341234 \
     -d "args=coffee"