> For the complete documentation index, see [llms.txt](https://web-push.spomky-labs.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://web-push.spomky-labs.com/3.1.x/common-concepts/the-subscription.md).

# The Subscription

The subscription is created on client side when the end-user allows your application to send push messages.

On client side (Javascript), you can simply send to your server the object you receive using `JSON.stringify`.

{% hint style="info" %}
Javascript examples to get a Subscription from the web browser are not provided here. Please refer to other resources such as blog posts or library documentation.
{% endhint %}

A subscription object will look like:

```javascript
{
 "endpoint":"https://updates.push.services.mozilla.com/wpush/v2/AAAAAAAA[…]AAAAAAAAA",
 "keys":{
 "auth":"XXXXXXXXXXXXXX",
 "p256dh":"YYYYYYYY[…]YYYYYYYYYYYYY"
 }
}
```

On server side, you can get a `WebPush\Subscription` object from the JSON string using the dedicated method `WebPush\Subscription::createFromString`.

```php
<?php

use WebPush\Subscription;

$subscription = Subscription::createFromString('{"endpoint":"https://updates.push.services.mozilla.com/wpush/v2/AAAAAAAA[…]AAAAAAAAA","keys":{"auth":"XXXXXXXXXXXXXX","p256dh":"YYYYYYYY[…]YYYYYYYYYYYYY"}}');
```

## Supported Content Encodings

By default, the content encoding `aesgcm` will be used. This encoding indicates how the payload of the notification should be formatted. The PushManager object from the Push API may list all acceptable encodings. In this case, it could be interesting to set these encodings to the Subscription object.

```javascript
// Retreive the supported content encodings
const supportedContentEncodings = PushManager.supportedContentEncodings || ['aesgcm'];

// Assign the encodings to the subscription object
const jsonSubscription = Object.assign(
    subscription.toJSON(),
    { supportedContentEncodings }
);

// Send the subscription object to the application server
fetch('/subscription/add', {
    method: 'POST',
    body: JSON.stringify(jsonSubscription),
});
```

This will result in something like as follow:

```javascript
{
 "endpoint":"https://updates.push.services.mozilla.com/wpush/v2/AAAAAAAA[…]AAAAAAAAA",
 "keys":{
 "auth":"XXXXXXXXXXXXXX",
 "p256dh":"YYYYYYYY[…]YYYYYYYYYYYYY",
 "supportedContentEncodings":["aes128gcm","aesgcm"]
 }
}
```

{% hint style="warning" %}
The order of `supportedContentEncodings` is important. First supported item will be used. If possible, `AES128GCM` should be used as prefered content encoding.
{% endhint %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://web-push.spomky-labs.com/3.1.x/common-concepts/the-subscription.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.