Cloud code triggered by Client SDK

    You will need lambda functions if you want to have codes written on the backend server instead of inside the SDK. The client SDK calls the cloud codes which in turn return the response back to the client.

    Typical usages include:

    • processing payment transactions
    • sending emails or SMS
    • running complex database queries that cannot be done with the SDKs efficiently
    • operations that requires permission checking from server side

    A lambda function can be created using the @skygear.op decorator.

    Decorator Parameters

    The decorator syntax is:

    @skygear.op(name, user_required=False, key_required=False)
    • name (String)

      It is an identifier for the lambda function. The client SDKs call this function using this name identifier.

    • user_required (boolean, optional)

      If user_required is set to True, only authenticated user can call this function. Skygear will return an PermissionDenied error if an unauthenticated user tries to call this function.

      The default value is False.

    • key_required (boolean, optional)

      If key_required is set to True, only authenticated user or client with API key can call this function. Skygear will return a NotAuthenticated error if an unauthenticated user and a client without API key tries to call this function.

      The default value is False. If user_required is set to True, this parameter is ignored.

    Passing arguments to Lambda Functions

    The lambda function can accept arguments. The list of arguments are defined in the function signature; and the SDK must provide those arguments when calling the lambda function. You can refer to the example for how to pass arguments to lambda functions.

    If a function takes no parameters, its signature should look like:

    def my_func():

    If a function takes two arguments, song_name and singer, its signature should look like:

    def my_func_two(song_name, singer):

    Each of the arguments can be one of the following types. They are similar to the available types in a JSON object.

    • Number
    • String
    • Boolean
    • Array
    • Object

    Depending on the SDKs, the supplied arguments will be passed to the lambda function as the corresponding data type.

    Tips: In the JS SDK, the parameters are parsed using the toJSON method. For example, a Date object in JS SDK will be passed to the lambda function in Python as a string like '2016-10-28T03:23:11.600Z'.

    Return Value

    A lambda function should return a JSON-serializable Python dictionary or None. It will be the response the client SDK receives.


    The following lambda function, named send_invitation_email, accepts two parameters: to_user_email and custom_message. It sends the email using SendGrid.

    import skygear
    # need to include sendgrid in requirements.txt
    import sendgrid
    def send_invitation_email(to_user_email, custom_message):
        email = sendgrid.Mail()
        email.set_subject('You are invited to try the app!')
        client = sendgrid.SendGridClient('my_api_key')
        return {
          'result': 'OK',

    This function can be invoked from the client SDKs by the followings:

    JS SDK

    const params = {
      'to_user_email': '',
      'custom_message': 'Hi there!',
    skygear.lambda('send_invitation_email', params)
      .then(response => {
        console.log(response); // {'result': 'OK'}

    Android SDK

    Container skygear = Container.defaultContainer(this);
    String lambdaName = "send_invitation_email";
    // Argument order follows the lambda function signature
    Object[] argv = new Object[]{ "", "Hi there!" };
    // Note: you can skip the argument when calling the function if there is none
    skygear.callLambdaFunction(lambdaName, argv, new LambdaResponseHandler() {
        public void onLambdaSuccess(JSONObject result) {
            // Your logic to handle the function result
        public void onLambdaFail(String reason) {
            // Error Handling

    iOS SDK

    NSArray *argv = @[@"", @"Hi there!"];
    [container callLambda:@"send_invitation_email" arguments:argv completionHandler:^(NSDictionary *response, NSError *error) {
        if (error) {
            NSLog(@"error calling send_invitation_email:someone: %@", error);
        NSLog(@"Received response = %@", response);