Firebase Cloud Messaging HTTP protocol

This document provides a reference for the HTTP syntax used to pass messages from your app server to client apps via Firebase Cloud Messaging. Your app server must direct all HTTP requests to this endpoint:

https://fcm.googleapis.com/fcm/send

The available parameters and options fall into the following broad categories:

Downstream message syntax
Downstream message error response codes

Downstream message syntax

This section gives the syntax for sending downstream messages and interpreting HTTP responses from Firebase Cloud Messaging.

Downstream HTTP messages (JSON)

The following table lists the targets, options, and payload for HTTP JSON messages.

Table 1. Targets, options, and payload for downstream HTTP messages (JSON).

Parameter	Usage	Description
Targets
`to`	Optional, string	This parameter specifies the recipient of a message. The value can be a device's registration token, a device group's notification key, or a single topic (prefixed with `/topics/`). To send to multiple topics, use the `condition` parameter.
`registration_ids`	Optional, array of strings	This parameter specifies the recipient of a multicast message, a message sent to more than one registration token. The value should be an array of registration tokens to which to send the multicast message. The array must contain at least 1 and at most 1000 registration tokens. To send a message to a single device, use the `to` parameter. Multicast messages are only allowed using the HTTP JSON format.
`condition`	Optional, string	This parameter specifies a logical expression of conditions that determine the message target. Supported condition: Topic, formatted as "'yourTopic' in topics". This value is case-insensitive. Supported operators: `&&`, `\|\|`. Maximum two operators per topic message supported.
`notification_key` Deprecated	Optional, string	This parameter is deprecated. Instead, use `to` to specify message recipients. For more information on how to send messages to multiple devices, see the documentation for your platform.
Options
`collapse_key`	Optional, string	This parameter identifies a group of messages (e.g., with `collapse_key: "Updates Available"`) that can be collapsed, so that only the last message gets sent when delivery can be resumed. This is intended to avoid sending too many of the same messages when the device comes back online or becomes active. Note that there is no guarantee of the order in which messages get sent. Note: A maximum of 4 different collapse keys is allowed at any given time. This means a FCM connection server can simultaneously store 4 different messages per client app. If you exceed this number, there is no guarantee which 4 collapse keys the FCM connection server will keep.
`priority`	Optional, string	Sets the priority of the message. Valid values are "normal" and "high." On iOS, these correspond to APNs priorities 5 and 10. By default, notification messages are sent with high priority, and data messages are sent with normal priority. Normal priority optimizes the client app's battery consumption and should be used unless immediate delivery is required. For messages with normal priority, the app may receive the message with unspecified delay. When a message is sent with high priority, it is sent immediately, and the app can display a notification.
`content_available`	Optional, boolean	On iOS, use this field to represent `content-available` in the APNs payload. When a notification or message is sent and this is set to `true`, an inactive client app is awoken, and the message is sent through APNs as a silent notification and not through the FCM connection server. Note that silent notifications in APNs are not guaranteed to be delivered, and can depend on factors such as the user turning on Low Power Mode, force quitting the app, etc. On Android, data messages wake the app by default. On Chrome, currently not supported.