Run functions locally

The Firebase CLI includes a Cloud Functions emulator which can emulate the following function types:

  • HTTPS functions
  • Callable functions
  • Background functions triggered from Firebase Authentication, Realtime Database, Cloud Firestore, Cloud Storage and Cloud Pub/Sub.

You can run functions locally to test them before deploying to production.

Install the Firebase CLI

To use the Cloud Functions emulator, first install the Firebase CLI:

npm install -g firebase-tools

In order to use the local emulator, your Cloud Functions must depend on:

  • firebase-admin version 8.0.0 or higher.
  • firebase-functions version 3.0.0 or higher.

Set up admin credentials (optional)

If you want your functions tests to interact with Google APIs or other Firebase APIs via the Firebase Admin SDK, you may need to set up admin credentials.

  • Cloud Firestore and Realtime Database triggers already have sufficient credentials, and do not require additional setup.
  • All other APIs, including Firebase APIs such as Authentication and FCM or Google APIs such as Cloud Translation or Cloud Speech, require the setup steps described in this section. This applies whether you're using the Cloud Functions shell or firebase emulators:start.

To set up admin credentials for emulated functions:

  1. Open the Service Accounts pane of the Google Cloud console.
  2. Make sure that App Engine default service account is selected, and use the options menu at right to select Create key.
  3. When prompted, select JSON for the key type, and click Create.
  4. Set your Google default credentials to point to the downloaded key:


    export GOOGLE_APPLICATION_CREDENTIALS="path/to/key.json"
    firebase emulators:start


    firebase emulators:start

After completing these steps, your functions tests can access Firebase and Google APIs using the Admin SDK. For example, when testing an Authentication trigger, the emulated function could call admin.auth().getUserByEmail(email).

Set up functions configuration (optional)

If you're using custom functions configuration variables, first run the command to get your custom config (run this within the functions directory) in your local environment:

firebase functions:config:get > .runtimeconfig.json
# If using Windows PowerShell, replace the above with:
# firebase functions:config:get | ac .runtimeconfig.json

Run the emulator suite

To run the Cloud Functions emulator, use the emulators:start command:

firebase emulators:start

The emulators:start command will start emulators for Cloud Functions, Cloud Firestore, Realtime Database, and Firebase Hosting based on the products you have initialized in your local project using firebase init. If you want to start a particular emulator, use the --only flag:

firebase emulators:start --only functions

If you want to run a test suite or testing script after the emulators have started, use the emulators:exec command:

firebase emulators:exec "./"

Instrument your app to talk to the emulators

To instrument your app to interact with the emulators, you may need to do some additional configuration.

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:

// is the special IP address to connect to the 'localhost' of
// the host computer from an Android emulator.
val functions = Firebase.functions
functions.useEmulator("", 5001)
// is the special IP address to connect to the 'localhost' of
// the host computer from an Android emulator.
FirebaseFunctions functions = FirebaseFunctions.getInstance();
functions.useEmulator("", 5001);
Functions.functions().useFunctionsEmulator(origin: "")

Web modular API

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

const functions = getFunctions(getApp());
connectFunctionsEmulator(functions, "", 5001);

Web namespaced API

firebase.functions().useEmulator("", 5001);

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:


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


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, modify back-end resources using the Emulator Suite UI, or by connecting your app or test code to the emulators using the SDK for your platform.

Test handlers for custom events emitted by Extensions

For functions you implement to handle Firebase Extensions custom events with Cloud Functions v2, the Cloud Functions emulator pairs with the Eventarc emulator to support Eventarc triggers.

To test custom event handlers for extensions that emit events, you must install the Cloud Functions and Eventarc emulators.

The Cloud Functions runtime sets the EVENTARC_EMULATOR environment variable to localhost:9299 in the current process if the Eventarc emulator is running. The Firebase Admin SDKs automatically connect to the Eventarc emulator when the EVENTARC_EMULATOR environment variable is set. You can modify the default port as discussed under Configure Local Emulator Suite.

When environment variables are properly configured, the Firebase Admin SDK automatically sends events to the Eventarc emulator. In turn, the Eventarc emulator makes a call back to the Cloud Functions emulator to trigger any registered handlers.

You can check Functions logs in the Emulator Suite UI for details on handler execution.

Interactions with other services

The emulator suite includes multiple emulators, which enable testing of cross-product interactions.

Cloud Firestore

If you have functions that use the Firebase Admin SDK to write to Cloud Firestore, these writes will be sent to the Cloud Firestore emulator if it is running. If further functions are triggered by those writes, they will be run in the Cloud Functions emulator.

Cloud Storage

If you have functions that use the Firebase Admin SDK (version 9.7.0 or greater) to write to Cloud Storage, these writes will be sent to the Cloud Storage emulator if it is running. If further functions are triggered by those writes, they will be run in the Cloud Functions emulator.

Firebase Authentication

If you have functions that use the Firebase Admin SDK (version 9.3.0 or greater) to write to Firebase Authentication, these writes will be sent to the Auth emulator if it is running. If further functions are triggered by those writes, they will be run in the Cloud Functions emulator.

Firebase Hosting

If you’re using Cloud Functions to generate dynamic content for Firebase Hosting, firebase emulators:start uses your local HTTP functions as proxies for hosting.


The emulator streams logs from your functions to the terminal window where they run. It displays all output from console.log(),, console.error(), and console.warn() statements inside your functions.

Next Steps

For a full example of using the Firebase emulator suite, see the testing quickstart sample.