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Reference: Notifications Spec

Mini Apps can send notifications to users who have added the Mini App to their Farcaster client and enabled notifications. An in-app notification is sent to a user and launches them into the app

Overview

At a high-level notifications work like so:

• when a user enables notifications for your app, their Farcaster client (i.e. Warpcast) will generate a unique notification token and send it to your server
• to send a notification to a user, make a request to the Farcaster client’s servers with the notification token and content
• if a user later disables notifications, you’ll receive another event indicating the user is unsubscribed and the notification token is no longer valid

Terms

To make our life easier, let’s call:

• Farcaster Client: An application like Warpcast that is able to display Mini Apps.
• Notification Server: Your server (see below).
• (Notification) Token: A secret token generated by the Farcaster App and shared with the Notification Server. A token is unique for each (Farcaster Client, Mini App, user Fid) tuple.

A notification token is basically a permission that a Farcaster client gives your app (on behalf of a user) to send them notifications.

Steps

1. Listen for events
   You’ll need a notification server to receive webhook events and a database to store notification tokens for users:

   • Managed
     • If you’d rather stay focused on your app, use Neynar to manage notification tokens on your behalf. Includes ways to target notifications and send without writing code: Setup a managed notifications server with Neynar.
   • Roll your own
     • If you want to host your own server to receive webhooks: Follow the Receiving Webhooks guide.

2. Add your webhook URL in farcaster.json
   If you haven’t already, follow the Publishing your app guide to host a farcaster.json on your app’s domain. Define the webhookUrl property in your app’s configuration in farcaster.json:

{
  "accountAssociation": {
    "header": "eyJmaWQiOjU0NDgsInR5cGUiOiJjdXN0b2R5Iiwia2V5IjoiMHg2MWQwMEFENzYwNjhGOEQ0NzQwYzM1OEM4QzAzYUFFYjUxMGI1OTBEIn0",
    "payload": "eyJkb21haW4iOiJleGFtcGxlLmNvbSJ9",
    "signature": "MHg3NmRkOWVlMjE4OGEyMjliNzExZjUzOTkxYTc1NmEzMGZjNTA3NmE5OTU5OWJmOWFmYjYyMzAyZWQxMWQ2MWFmNTExYzlhYWVjNjQ3OWMzODcyMTI5MzA2YmJhYjdhMTE0MmRhMjA4MmNjNTM5MTJiY2MyMDRhMWFjZTY2NjE5OTFj"
  },
  "miniapp": {
    "version": "1",
    "name": "Example App",
    "iconUrl": "https://example.com/icon.png",
    "homeUrl": "https://example.com",
    "imageUrl": "https://example.com/image.png",
    "buttonTitle": "Check this out",
    "splashImageUrl": "https://example.com/splash.png",
    "splashBackgroundColor": "#eeccff",
    "webhookUrl": "https://example.com/api/webhook"
  }
}

For a real example, this is Yoink’s manifest: https://yoink.party/.well-known/farcaster.json

3. Get users to add your app
   For a Mini App to send notifications, it needs to first be added by a user to their Farcaster client and for notifications to be enabled. Use the addMiniApp action while a user is using your app to prompt them to add it:

4. Caution
   The addMiniApp() action only works when your app is deployed to its production domain (matching your manifest). It will not work with tunnel domains during development.

5. Save the notification tokens
   When notifications are enabled, the Farcaster client generates a unique notification token for the user. This token is sent to webhookUrl defined in your farcaster.json along with a url that the app should call to send a notification. The token and url need to be securely saved to the database so they can be looked up when you want to send a notification to a particular user.

6. Send a notification
   Once you have a notification token for a user, you can send them a notification by sending a POST request to the url associated with that token.

If you are sending the same notification to multiple users, you batch up to a 100 sends in a single request by providing multiple tokens. You can safely use the same notificationId for all batches.

The body of that request must match the following JSON schema:

The targetUrl hostname must exactly match the domain your Mini App is registered on. Subdomains matter: if your app is on example.com, using www.example.com in the targetUrl will cause a target_url_mismatch error and the affected tokens will be permanently invalidated.

The server should respond with an HTTP 200 OK and the following JSON body:

When a user clicks the notification, the Farcaster client will:

• Open your Mini App at targetUrl
• Set the context.location to a MiniAppLocationNotificationContext

export type MiniAppLocationNotificationContext = {
  type: 'notification';
  notification: {
    notificationId: string;
    title: string;
    body: string;
  };
};

Avoid duplicate notifications

To avoid duplicate notifications, specify a stable notificationId for each notification you send. This identifier is joined with the FID (e.g. (fid, notificationId) to create a unique key that is used to deduplicate requests to send a notification over a 24 hour period. For example, if you want to send a daily notification to users you could use daily-reminder-05-06-2024 as your notificationId. Now you can safely retry requests to send the daily reminder notifications within a 24 hour period.

Rate Limits

Host servers may impose rate limits per token. The standard rate limits, which are enforced by Warpcast, are:

• 1 notification per 30 seconds per token
• 100 notifications per day per token

Receiving webhooks

Users can add and configure notification settings Mini Apps within their Farcaster client. When this happens Farcaster clients will send events to your server that include data relevant to the event. This allows your app to:

• keep track of what users have added or removed your app
• securely receive tokens that can be used to send notifications to your users

Events

miniapp_added

Sent when the user adds the Mini App to their Farcaster client (whether or not this was triggered by an addMiniApp() prompt). The optional notificationDetails object provides the token and url if the client equates adding to enabling notifications (Warpcast does this).

Payload

{
  "event": "miniapp_added",
  "notificationDetails": {
    "url": "https://api.farcaster.xyz/v1/frame-notifications",
    "token": "a05059ef2415c67b08ecceb539201cbc6"
  }
}

miniapp_removed

Sent when a user removes a mini app, which means that any notification tokens for that fid and client app (based on signer requester) should be considered invalid:

Payload

{
  "event": "miniapp_removed"
}

notifications_disabled

Sent when a user disables notifications from e.g. a settings panel in the client app. Any notification tokens for that fid and client app (based on signer requester) should be considered invalid:

Payload

{
  "event": "notifications_disabled"
}

notifications_enabled

Sent when a user enables notifications (e.g. after disabling them). The payload includes a new token and url:

Payload

{
  "event": "notifications_enabled",
  "notificationDetails": {
    "url": "https://api.farcaster.xyz/v1/frame-notifications",
    "token": "a05059ef2415c67b08ecceb539201cbc6"
  }
}

Handling events

Farcaster clients will POST events to the webhookUrl specified in your farcaster.json. Your endpoint should:

• verify the event
• persist relevant data
• return a 200 response

If your app doesn’t respond with a 200, the Farcaster client will attempt to re-send the event. The exact number of retries is up to each client.

Verifying events

Events are signed by the app key of a user with a JSON Farcaster Signature. This allows Mini Apps to verify the Farcaster client that generated the notification and the Farcaster user they generated it for. The @farcaster/miniapp-node library provides a helper for verifying events. To use it, you’ll need to supply a validation function that can check the signatures against the latest Farcaster network state. An implementation that uses Neynar is provided. You can sign up and get an API key on their free tier. Make sure to set NEYNAR_API_KEY environment variable.

Example

const requestJson = "base64encodeddata";

import {
  ParseWebhookEvent,
  parseWebhookEvent,
  verifyAppKeyWithNeynar,
} from "@farcaster/miniapp-node";

try {
  const data = await parseWebhookEvent(requestJson, verifyAppKeyWithNeynar);
} catch (e: unknown) {
  const error = e as ParseWebhookEvent.ErrorType;

switch (error.name) {
    case "VerifyJsonFarcasterSignature.InvalidDataError":
    case "VerifyJsonFarcasterSignature.InvalidEventDataError":
      // The request data is invalid
    case "VerifyJsonFarcasterSignature.InvalidAppKeyError":
      // The app key is invalid
    case "VerifyJsonFarcasterSignature.VerifyAppKeyError":
      // Internal error verifying the app key (caller may want to try again)
  }
}

Reference implementation

For a complete example, check out the Mini App V2 Demo which has all of the above:

• Handles webhooks leveraging the @farcaster/miniapp-node library that makes this very easy
• Saves notification tokens to Redis
• Sends notifications