Connect your app to the Cloud Functions Emulator

Before connecting your app to the Cloud Functions emulator, make sure that you understand the overall Firebase Local Emulator Suite workflow and that you install and configure the Local Emulator Suite.

Note: The Firebase Local Emulator Suite emulates a single Firebase project. If you want to emulate cross-service interactions such as database-triggered Cloud Functions or Rules that rely on Authentication you must make sure that the project ID in your code (in initializeApp(), etc.) matches the project ID used by the Firebase CLI. To select a project in the CLI run firebase use or pass the --project flag to each command.

Instrument your app to talk to the emulators

Instrument your app for callable functions

If your prototype and test activities involve callable backend functions, configure interaction with the Cloud Functions for Firebase emulator like this:

Android

        // 10.0.2.2 is the special IP address to connect to the 'localhost' of
        // the host computer from an Android emulator.
        FirebaseFunctions functions = FirebaseFunctions.getInstance();
        functions.useEmulator("10.0.2.2.", 5001);
MainActivity.java

iOS - Swift

Functions.functions().useFunctionsEmulator(origin: "http://localhost:5001")
ViewController.swift

Web v8

firebase.functions().useEmulator("localhost", 5001);
emulator-suite.js

Web v9

Learn more about the tree-shakeable Web v9 modular SDK, currently in Beta.

import { getApp } from "firebase/app";
import { getFunctions, useFunctionsEmulator } from "firebase/functions";

const functions = getFunctions(getApp());
useFunctionsEmulator(functions, "localhost", 5001);
fb_functions_emulator_connect.js

Note: Android only. Android network security configuration policies may affect how your code interacts with the Cloud Functions emulator, which serves data locally via unencrypted HTTP. Starting with Android 9 (API level 28), clear text communication is disabled by default. You can set up a network_security_config.xml file to whitelist the Cloud Functions emulator for development on localhost. See the relevant Android developer documentation.

Instrument your app for HTTPS functions emulation

Each HTTPS function in your code will be served from the local emulator using the following URL format:

http://$HOST:$PORT/$PROJECT/$REGION/$NAME

For example a simple helloWorld function with the default host port and region would be served at:

https://localhost:5001/$PROJECT/us-central1/helloWorld

Instrument your app for background-triggered functions emulation

The Cloud Functions emulator supports background-triggered functions from the following sources:

• Realtime Database emulator
• Cloud Firestore emulator
• Authentication emulator
• Pub/Sub emulator

To trigger background events, connect your app or test code to the emulators using the SDK for your platform.

What next?

• For a curated set of videos and detailed how-to examples, follow the Firebase Emulators Training Playlist.
• Learn more about the Cloud Functions for Firebase emulator at Run functions locally.