To get started with Cloud Functions, try working through this tutorial,
which starts with the required setup tasks and works through creating, testing,
and deploying two related functions:
- An "add message" function that exposes a URL that accepts a text value and writes it to Cloud Firestore.
- A "make uppercase" function that triggers on a Cloud Firestore write and transforms the text to uppercase.
Here's the full sample code containing the functions:
### Node.js
```javascript
// The Cloud Functions for Firebase SDK to create Cloud Functions and triggers.
const {logger} = require("firebase-functions");
const {onRequest} = require("firebase-functions/https");
const {onDocumentCreated} = require("firebase-functions/firestore");
// The Firebase Admin SDK to access Firestore.
const {initializeApp} = require("firebase-admin/app");
const {getFirestore} = require("firebase-admin/firestore");
initializeApp();
// Take the text parameter passed to this HTTP endpoint and insert it into
// Firestore under the path /messages/:documentId/original
exports.addmessage = onRequest(async (req, res) => {
// Grab the text parameter.
const original = req.query.text;
// Push the new message into Firestore using the Firebase Admin SDK.
const writeResult = await getFirestore()
.collection("messages")
.add({original: original});
// Send back a message that we've successfully written the message
res.json({result: `Message with ID: ${writeResult.id} added.`});
});
// Listens for new messages added to /messages/:documentId/original
// and saves an uppercased version of the message
// to /messages/:documentId/uppercase
exports.makeuppercase = onDocumentCreated("/messages/{documentId}", (event) => {
// Grab the current value of what was written to Firestore.
const original = event.data.data().original;
// Access the parameter `{documentId}` with `event.params`
logger.log("Uppercasing", event.params.documentId, original);
const uppercase = original.toUpperCase();
// You must return a Promise when performing
// asynchronous tasks inside a function
// such as writing to Firestore.
// Setting an 'uppercase' field in Firestore document returns a Promise.
return event.data.ref.set({uppercase}, {merge: true});
});
```
### Python
```python
# The Cloud Functions for Firebase SDK to create Cloud Functions and set up triggers.
from firebase_functions import firestore_fn, https_fn
# The Firebase Admin SDK to access Cloud Firestore.
from firebase_admin import initialize_app, firestore
import google.cloud.firestore
app = initialize_app()
@https_fn.on_request()
def addmessage(req: https_fn.Request) -> https_fn.Response:
"""Take the text parameter passed to this HTTP endpoint and insert it into
a new document in the messages collection."""
# Grab the text parameter.
original = req.args.get("text")
if original is None:
return https_fn.Response("No text parameter provided", status=400)
firestore_client: google.cloud.firestore.Client = firestore.client()
# Push the new message into Cloud Firestore using the Firebase Admin SDK.
_, doc_ref = firestore_client.collection("messages").add({"original": original})
# Send back a message that we've successfully written the message
return https_fn.Response(f"Message with ID {doc_ref.id} added.")
@firestore_fn.on_document_created(document="messages/{pushId}")
def makeuppercase(event: firestore_fn.Event[firestore_fn.DocumentSnapshot | None]) -> None:
"""Listens for new documents to be added to /messages. If the document has
an "original" field, creates an "uppercase" field containg the contents of
"original" in upper case."""
# Get the value of "original" if it exists.
if event.data is None:
return
try:
original = event.data.get("original")
except KeyError:
# No "original" field, so do nothing.
return
# Set the "uppercase" field.
print(f"Uppercasing {event.params['pushId']}: {original}")
upper = original.upper()
event.data.reference.update({"uppercase": upper})
```
## About this tutorial
We've chosen Cloud Firestore and HTTP-triggered functions for this
sample in part because these background triggers can be thoroughly tested
through the [Firebase Local Emulator Suite](https://firebase.google.com/docs/emulator-suite.md.txt). This toolset
also supports Realtime Database, Cloud Storage,
PubSub, Auth, and HTTP callable triggers. Other types of background triggers
such as Remote Config and TestLab triggers can be
[tested interactively](https://firebase.google.com/docs/functions/local-shell.md.txt) using toolsets not
described in this page.
> [!NOTE]
> **Note:** You can emulate functions in any Firebase project, but to deploy functions, your project must be on the [Blaze pricing plan](https://firebase.google.com/pricing.md.txt). See [Cloud Functions pricing](https://firebase.google.com/docs/functions/faq-and-troubleshooting.md.txt#functions-pricing).
The following sections of this tutorial detail the steps required to build,
test, and deploy the sample.
## Create a Firebase Project
### New to Firebase or Cloud
Follow these steps if you're new to Firebase or Google Cloud.
You can also follow these steps if you want to create a wholly new
Firebase project (and its underlying Google Cloud project).
1. Sign into the [Firebase console](https://console.firebase.google.com/).
2. Click the button to create a new Firebase project.
3. In the text field, enter a **project name**.
If you're part of a Google Cloud org, you can optionally select which
folder you create your project in.
> [!CAUTION]
> Your project name is used as a display name in Firebase interfaces, and Firebase auto-creates a unique project ID based on this project name. Note that you can optionally click the **Edit** icon now to set your preferred project ID, but you cannot change this ID after project creation. Learn about [how Firebase uses the
> project ID](https://firebase.google.com/docs/projects/learn-more#project-id).
4. If prompted, review and accept the [Firebase terms](https://firebase.google.com/terms.md.txt), then click **Continue**.
5. *(Optional)* Enable AI assistance in the Firebase console (called "Gemini in Firebase"), which can help you get started and streamline your development process.
6. *(Optional)* Set up Google Analytics for your project,
which enables an optimal experience using these Firebase products:
[Firebase A/B Testing](https://firebase.google.com/docs/ab-testing.md.txt),
[Cloud Messaging](https://firebase.google.com/docs/cloud-messaging.md.txt),
[Crashlytics](https://firebase.google.com/docs/crashlytics.md.txt),
[In-App Messaging](https://firebase.google.com/docs/in-app-messaging.md.txt), and
[Remote Config](https://firebase.google.com/docs/remote-config.md.txt)
(including
[Personalization](https://firebase.google.com/docs/remote-config/personalization.md.txt)).
Either select an existing
[Google Analytics account](https://support.google.com/analytics/answer/1009618)
or create a new account. If you create a new account, select your
[Analytics reporting location](https://firebase.google.com/docs/projects/locations.md.txt),
then accept the data sharing settings and Google Analytics terms
for your project.
> [!NOTE]
> You can always set up Google Analytics later in the [*Integrations* tab](https://console.firebase.google.com/project/_/settings/integrations) of your *Project settings*.
7. Click **Create project**.
Firebase creates your project, provisions some initial resources, and
enables important APIs. When the process completes, you'll be taken to the
overview page for your Firebase project in the Firebase console.
### Existing Cloud project
Follow these steps if you want to start using Firebase with an existing
Google Cloud project. Learn more about and troubleshoot
["adding
Firebase" to an existing Google Cloud project](https://firebase.google.com/docs/projects/use-firebase-with-existing-cloud-project).
1. Sign into the [Firebase console](https://console.firebase.google.com/) with the account that gives you access to the existing Google Cloud project.
2. Click the button to create a new Firebase project.
3. At the bottom of the page, click **Add Firebase to Google Cloud project**.
4. In the text field, start entering the **project name** of the existing project, and then select the project from the displayed list.
5. Click **Open project**.
6. If prompted, review and accept the [Firebase terms](https://firebase.google.com/terms.md.txt), then click **Continue**.
7. *(Optional)* Enable AI assistance in the Firebase console (called "Gemini in Firebase"), which can help you get started and streamline your development process.
8. *(Optional)* Set up Google Analytics for your project,
which enables an optimal experience using these Firebase products:
[Firebase A/B Testing](https://firebase.google.com/docs/ab-testing.md.txt),
[Cloud Messaging](https://firebase.google.com/docs/cloud-messaging.md.txt),
[Crashlytics](https://firebase.google.com/docs/crashlytics.md.txt),
[In-App Messaging](https://firebase.google.com/docs/in-app-messaging.md.txt), and
[Remote Config](https://firebase.google.com/docs/remote-config.md.txt)
(including
[Personalization](https://firebase.google.com/docs/remote-config/personalization.md.txt)).
Either select an existing
[Google Analytics account](https://support.google.com/analytics/answer/1009618)
or create a new account. If you create a new account, select your
[Analytics reporting location](https://firebase.google.com/docs/projects/locations.md.txt),
then accept the data sharing settings and Google Analytics terms
for your project.
> [!NOTE]
> You can always set up Google Analytics later in the [*Integrations* tab](https://console.firebase.google.com/project/_/settings/integrations) of your *Project settings*.
9. Click **Add Firebase**.
Firebase
[adds
Firebase to your existing project](https://firebase.google.com/docs/projects/use-firebase-with-existing-cloud-project#faq_what-happens-when-add-firebase).
When the process completes, you'll be taken to the overview page for your
Firebase project in the Firebase console.
## Set up your environment and the Firebase CLI
### Node.js
You'll need a [Node.js](https://nodejs.org/) environment to write functions,
and you'll need the Firebase CLI to deploy functions to
the Cloud Functions runtime. For installing Node.js and [npm](https://www.npmjs.com/),
[Node Version Manager](https://github.com/creationix/nvm/blob/master/README.md)
is recommended.
> [!IMPORTANT]
> **Important:** Cloud Functions and the Firebase CLI fully support Node.js versions 20 and 22. Version 18 was deprecated in early 2025. See [Set runtime options](https://firebase.google.com/docs/functions/manage-functions.md.txt#set-runtime-options) for important information regarding ongoing support for these versions of Node.js.
Once you have Node.js and npm installed,
[install the Firebase CLI](https://firebase.google.com/docs/cli.md.txt#setup_update_cli)
via your preferred method. To install the CLI via npm, use:
`npm install -g firebase-tools`
This installs the globally available firebase command. If
the command fails, you may need to
[change npm permissions](https://docs.npmjs.com/getting-started/fixing-npm-permissions).
To update to the latest version of `firebase-tools`, rerun the same command.
> [!CAUTION]
> In many cases, new features and bug fixes are
> available only with the latest version of the Firebase CLI and the
> `firebase-functions` SDK. It's a good practice to frequently
> update both the Firebase CLI and the SDK with these commands
> inside the `functions` folder of your Firebase project:
>
> ```
> npm install firebase-functions@latest firebase-admin@latest --save
> npm install -g firebase-tools
> ```
### Python
You'll need a [Python](https://python.org) environment
to write functions,
and you'll need the Firebase CLI to deploy functions to
the Cloud Functions runtime. We recommend using `venv` to
isolate dependencies. Python versions 3.10 through 3.13 are supported,
with 3.13 being the default runtime.
Once you have Python installed,
[install the Firebase CLI](https://firebase.google.com/docs/cli.md.txt#setup_update_cli)
via your preferred method.
> [!CAUTION]
> In many cases, new features and bug fixes are
> available only with the latest version of the Firebase CLI and the
> `firebase-functions` SDK. It's a good practice to frequently
> update both the Firebase CLI and the SDK
> inside the `functions` folder of your Firebase project.
## Initialize your project
When you initialize Firebase SDK for Cloud Functions, you create an empty project
containing dependencies and some minimal sample code. If you are
using Node.js, you can choose either
TypeScript or JavaScript for composing functions. For the purposes of this
tutorial, you'll also need to initialize Cloud Firestore.
To initialize your project:
1. Run `firebase login` to log in via the browser and authenticate the Firebase CLI.
2. Go to your Firebase project directory.
3. Run `firebase init firestore`. For this tutorial, you can accept the default values when prompted for Firestore rules and index files. If you haven't used Cloud Firestore in this project yet, you'll also need to select a starting mode and location for Firestore as described in [Get started with Cloud Firestore](https://firebase.google.com/docs/firestore/quickstart.md.txt#create).
4. Run `firebase init functions`. The CLI prompts you to choose an existing codebase or initialize and name a new one. When you're just getting started, a single codebase in the default location is adequate; later, as your implementation expands, you might want to [organize functions in codebases](https://firebase.google.com/docs/functions/organize-functions.md.txt#organize_functions_in_codebases).
5. The CLI gives you these options for language support:
- JavaScript
- TypeScript
- Python
For this tutorial, select **JavaScript** or **Python** . For authoring in
TypeScript, see [Write Functions with TypeScript](https://firebase.google.com/docs/functions/typescript.md.txt).
6. The CLI gives you an option to install dependencies. This is safe
to decline if you want to manage dependencies in another way.
After these commands complete successfully, your project structure looks like
this:
### Node.js
myproject
+- .firebaserc # Hidden file that helps you quickly switch between
| # projects with `firebase use`
|
+- firebase.json # Describes properties for your project
|
+- functions/ # Directory containing all your functions code
|
+- .eslintrc.json # Optional file containing rules for JavaScript linting.
|
+- package.json # npm package file describing your Cloud Functions code
|
+- index.js # Main source file for your Cloud Functions code
|
+- node_modules/ # Directory where your dependencies (declared in
# package.json) are installed
For Node.js, the `package.json` file created during initialization contains an important
key: `"engines": {"node": "18"}`. This specifies your Node.js version for
writing and deploying functions. You can
[select other supported versions](https://firebase.google.com/static/docs/functions/manage-functions#set-node.js).
### Python
myproject
+- .firebaserc # Hidden file that helps you quickly switch between
| # projects with `firebase use`
|
+- firebase.json # Describes properties for your project
|
+- functions/ # Directory containing all your functions code
|
+- main.py # Main source file for your Cloud Functions code
|
+- requirements.txt # List of the project's modules and packages
|
+- venv/ # Directory where your dependencies are installed
## Import the required modules and initialize an app
After you have completed the setup tasks, you can
open the source directory and start adding code as described in the
following sections. For this sample, your project must import the
Cloud Functions and Admin SDK modules. Add lines
like the following to your source file:
### Node.js
```javascript
// The Cloud Functions for Firebase SDK to create Cloud Functions and triggers.
const {logger} = require("firebase-functions");
const {onRequest} = require("firebase-functions/https");
const {onDocumentCreated} = require("firebase-functions/firestore");
// The Firebase Admin SDK to access Firestore.
const {initializeApp} = require("firebase-admin/app");
const {getFirestore} = require("firebase-admin/firestore");
initializeApp();
```
### Python
```python
# The Cloud Functions for Firebase SDK to create Cloud Functions and set up triggers.
from firebase_functions import firestore_fn, https_fn
# The Firebase Admin SDK to access Cloud Firestore.
from firebase_admin import initialize_app, firestore
import google.cloud.firestore
app = initialize_app()
```
These lines load the required modules and
initialize an `admin` app instance from which Cloud Firestore changes can be made.
Wherever [Admin SDK](https://firebase.google.com/docs/admin/setup.md.txt) support is available, as it is
for FCM, Authentication, and Firebase Realtime Database, it provides a
powerful way to integrate Firebase using Cloud Functions.
The Firebase CLI automatically
installs the Firebase Admin SDK and Firebase SDK for Cloud Functions modules when you initialize
your project. For more information about adding 3rd party libraries
to your project, see
[Handle Dependencies](https://firebase.google.com/docs/functions/handle-dependencies.md.txt).
## Add the "add message" function
For the "add message" function, add these lines to your source file:
### Node.js
```javascript
// Take the text parameter passed to this HTTP endpoint and insert it into
// Firestore under the path /messages/:documentId/original
exports.addmessage = onRequest(async (req, res) => {
// Grab the text parameter.
const original = req.query.text;
// Push the new message into Firestore using the Firebase Admin SDK.
const writeResult = await getFirestore()
.collection("messages")
.add({original: original});
// Send back a message that we've successfully written the message
res.json({result: `Message with ID: ${writeResult.id} added.`});
});
```
### Python
```python
@https_fn.on_request()
def addmessage(req: https_fn.Request) -> https_fn.Response:
"""Take the text parameter passed to this HTTP endpoint and insert it into
a new document in the messages collection."""
# Grab the text parameter.
original = req.args.get("text")
if original is None:
return https_fn.Response("No text parameter provided", status=400)
firestore_client: google.cloud.firestore.Client = firestore.client()
# Push the new message into Cloud Firestore using the Firebase Admin SDK.
_, doc_ref = firestore_client.collection("messages").add({"original": original})
# Send back a message that we've successfully written the message
return https_fn.Response(f"Message with ID {doc_ref.id} added.")
```
The "add message" function is an HTTP endpoint. Any request to the endpoint
results in request and response objects passed to the
the request handler for your platform ([`onRequest()`](https://firebase.google.com/docs/reference/functions/2nd-gen/node/firebase-functions.https.md.txt#httpsonrequest)
or [`on_request`](https://firebase.google.com/docs/reference/functions/python/firebase_functions.https_fn#on_request)).
HTTP functions are synchronous (similar to
[callable functions](https://firebase.google.com/docs/functions/callable.md.txt)), so you should send a response
as quickly as possible and defer work using Cloud Firestore. The "add message"
HTTP function passes a text value to the HTTP endpoint and inserts it into the
database under the path `/messages/:documentId/original`.
## Add the "make uppercase" function
For the "make uppercase" function, add these lines to your source file:
### Node.js
```javascript
// Listens for new messages added to /messages/:documentId/original
// and saves an uppercased version of the message
// to /messages/:documentId/uppercase
exports.makeuppercase = onDocumentCreated("/messages/{documentId}", (event) => {
// Grab the current value of what was written to Firestore.
const original = event.data.data().original;
// Access the parameter `{documentId}` with `event.params`
logger.log("Uppercasing", event.params.documentId, original);
const uppercase = original.toUpperCase();
// You must return a Promise when performing
// asynchronous tasks inside a function
// such as writing to Firestore.
// Setting an 'uppercase' field in Firestore document returns a Promise.
return event.data.ref.set({uppercase}, {merge: true});
});
```
### Python
```python
@firestore_fn.on_document_created(document="messages/{pushId}")
def makeuppercase(event: firestore_fn.Event[firestore_fn.DocumentSnapshot | None]) -> None:
"""Listens for new documents to be added to /messages. If the document has
an "original" field, creates an "uppercase" field containg the contents of
"original" in upper case."""
# Get the value of "original" if it exists.
if event.data is None:
return
try:
original = event.data.get("original")
except KeyError:
# No "original" field, so do nothing.
return
# Set the "uppercase" field.
print(f"Uppercasing {event.params['pushId']}: {original}")
upper = original.upper()
event.data.reference.update({"uppercase": upper})
```
The "make uppercase" function executes when Cloud Firestore is written to,
defining the document to listen on. For performance reasons, you
should be as specific as possible.
Braces---for example, `{documentId}`---surround "parameters," wildcards
that expose their matched data in the callback. Cloud Firestore triggers the
callback whenever new messages are added.
> [!CAUTION]
> **Caution:** Be careful to avoid any situation in which the function's result actually retriggers the function, creating an infinite loop --- for example, a function triggered by writes to a specific Cloud Firestore document that terminates by writing to that same path. Also make sure to write functions in an [idempotent](https://en.wikipedia.org/wiki/Idempotence) way, so that they produce the same result if they run multiple times for a single event.
In Node.js, event-driven functions such as Cloud Firestore events are
asynchronous. The callback function should return either a `null`, an Object,
or a [Promise](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise).
If you do not return anything, the function times out, signaling an error, and
is retried. See [Sync, Async, and Promises](https://firebase.google.com/docs/functions/terminate-functions.md.txt).
## Emulate execution of your functions
The
[Firebase Local Emulator Suite](https://firebase.google.com/docs/emulator-suite.md.txt)
allows you to build and test apps on your local machine instead of deploying to
a Firebase project. Local testing during development is strongly recommended,
in part because it lowers the risk from coding errors that could potentially
incur cost in a production environment (for example, an infinite loop).
To emulate your functions:
1. Run `firebase emulators:start` and check the output for the URL
of the Emulator Suite UI. It defaults to
[localhost:4000](http://localhost:4000), but may be hosted on a different
port on your machine. Enter that URL in your browser to open the
Emulator Suite UI.
2. Check the output of the `firebase emulators:start`
command for the URL
of the HTTP function. It will look similar to
`http://localhost:5001/MY_PROJECT/us-central1/addMessage`, except that:
1. `MY_PROJECT` will be replaced with your project ID.
2. The port may be different on your local machine.
3. Add the query string `?text=uppercaseme` to the end of the function's URL.
This should look something like:
`http://localhost:5001/MY_PROJECT/us-central1/addMessage?text=uppercaseme`.
Optionally, you can change the message "uppercaseme" to a custom
message.
4. Create a new message by opening the URL in a new tab in your browser.
5. View the effects of the functions in the Emulator Suite UI:
1. In the **Logs** tab, you should see new logs indicating that
your HTTP functions ran successfully:
`i functions: Beginning execution of "addMessage"`
`i functions: Beginning execution of "makeUppercase"`
2. In the **Firestore** tab, you should see a document containing your original
message as well as the uppercased version of your message (if it was
originally "uppercaseme", you'll see "UPPERCASEME").
## Deploy functions to a production environment
Once your functions are working as desired in the emulator, you can proceed to
deploying, testing, and running them in the production environment. Keep in mind
that to deploy in production, your project
must be on the [Blaze pricing plan](https://firebase.google.com/pricing.md.txt). See
[Cloud Functions pricing](https://firebase.google.com/docs/functions/faq-and-troubleshooting.md.txt#functions-pricing).
To complete the tutorial, deploy your functions and then execute
them.
1. Run this command to deploy your functions:
```
firebase deploy --only functions
```
After you run this command, the Firebase CLI outputs the URL for any
HTTP function
endpoints. In your terminal, you should see a line like the following:
Function URL (addMessage): https://us-central1-MY_PROJECT.cloudfunctions.net/addMessage
The URL contains your project ID as well as a region for the HTTP
function. Though you don't need to worry about it now, some production HTTP
functions should specify a [location](https://firebase.google.com/docs/functions/locations.md.txt) to
minimize network latency.
If you encounter access errors such as "Unable to authorize access to
project," try checking your [project aliasing](https://firebase.google.com/docs/cli.md.txt#project_aliases).
2. Using the URL output by the CLI, add a text query parameter,
and open it in a browser:
https://us-central1-MY_PROJECT.cloudfunctions.net/addMessage?text=uppercasemetoo
The function executes and redirects the browser to the
Firebase console at the database location
where the text string is stored. This
write event triggers the "make uppercase" function, which writes an uppercase
version of the string.
After deploying and executing functions, you can
view logs in the [Google Cloud console](https://console.cloud.google.com/functions/list).
If you need to [delete functions](https://firebase.google.com/docs/functions/manage-functions.md.txt#delete-functions)
in development or production, use the Firebase CLI.
In production, you may want to optimize function performance and control
costs by setting minimum and maximum numbers of instances to run. See
[Control scaling behavior](https://firebase.google.com/docs/functions/manage-functions.md.txt#min-max-instances)
for more information on these runtime options.
> [!NOTE]
> **Note:** Deployment of functions from Firebase CLI is subject to rate limits. See [Quota limits for Firebase CLI deployment](https://firebase.google.com/docs/functions/quotas.md.txt#quota_limits_for_firebase_cli_deployment).
## Next steps
In this documentation, you can learn more about how to
[manage functions](https://firebase.google.com/docs/functions/manage-functions.md.txt) for Cloud Functions
as well as how to
to handle all event types supported by Cloud Functions.
To learn more about Cloud Functions, you
could also do the following:
- Read about [use cases for Cloud Functions](https://firebase.google.com/docs/functions/use-cases.md.txt).
- Try the [Cloud Functions codelab](https://codelabs.developers.google.com/codelabs/firebase-cloud-functions/#0).
- Review and run [code samples on GitHub](https://github.com/firebase/functions-samples)