# Content Launch

**Clear LRS** implements the [**Rustici Launch Mechanism**](https://github.com/RusticiSoftware/launch/blob/master/lms_lrs.md) when passing the authenticated user to learning content for the purpose of storing data in the LRS. This is a popular mechanism supported by most authoring tools.

When content is launched from the LRS, the launch page will be loaded with the following query parameters:

| Query Parameter  | Description                                                                                                                                                                                                                                     |
| ---------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **endpoint**     | <p>The base path for all xAPI requests.</p><p>e.g. <code><https://org.clearlrs.com/xapi/></code></p>                                                                                                                                            |
| **auth**         | <p>An authentication token to be sent with every xAPI request.</p><p>e.g. <code>Basic a2V5OnNlY3JldA==</code></p>                                                                                                                               |
| **actor**        | <p>The <strong>actor</strong> object representing the user launching the content.</p><p>e.g. <code>{"mbox":"mailto:<learner@example.com>"}</code></p>                                                                                           |
| **activity\_id** | <p>The root <strong>activity ID</strong> for the content being launched. This should be used as the <strong>parent</strong> or <strong>grouping</strong> for all statements.</p><p>e.g. <code><http://example.com/learning/activity></code></p> |
| **registration** | <p>An optional <strong>registration</strong> value to be sent in the <strong>context</strong> field of any statements generated.</p><p>e.g. <code>231859e2-937f-4969-b069-91cf49bfea0c</code></p>                                               |

{% hint style="info" %}
Although the above examples are provided in clear text, each query parameter value will actually be [**URL Encoded**](https://en.wikipedia.org/wiki/Percent-encoding) to prevent malforming the launch URL.
{% endhint %}

For the above example, assuming the content being launched existed at the following address – `https://content.example.com/index.html` – then the launch URL would look like the below (new lines added for readability):

```
https://content.example.com/index.html
?endpoint=https%3A%2F%2Forg.clearlrs.com%2Fxapi%2F
&auth=Basic%20a2V5OnNlY3JldA%3D%3D
&actor=%7B%22mbox%22%3A%22mailto%3Alearner%40example.com%22%7D
&activity_id=http%3A%2F%2Fexample.com%2Flearning%2Factivity
&registration=231859e2-937f-4969-b069-91cf49bfea0c
```

Once launched, the activity provider should parse and decode these parameters and use them as appropriate when generating statements.&#x20;

{% hint style="warning" %}
**It is the Activity Provider's responsibility to respect every parameter passed to it, even if its internal representation differs.**&#x20;

Sometimes the LRS will force a new **registration** or override the **Activity ID** in response to user actions so the content is required to send statements using the received values to preserve data integrity.
{% endhint %}