Which HTTP request headers are used by Matomo?

When measuring activity with the [Matomo Tracking API](https://developer.matomo.org/api-reference/tracking-api), the following HTTP headers may be used:

* `Host` – the hostname of the HTTP request, the hostname of the Matomo server.
* `Referer` – used to track Referrer information such as website, search engine, social network.
* `User-Agent` – used to detect the information about browsers, operating system, devices by [device-detector library](https://matomo.org/blog/2014/07/new-project-devicedetector/).
* `Cookie` – when [Opted-out from tracking](https://matomo.org/faq/general/faq_20000/), or when [Third party cookies](https://matomo.org/faq/how-to/faq_118/) are used.
* `Origin` – used when [cross-origin resource sharing](https://matomo.org/faq/how-to/faq_18694/) is enabled.
* `Accept-Language` – used to detect the users’ language
* `X-Forwarded-Proto`, `X-Forwarded-Host`, `X-Forwarded-For` – when Matomo is [setup behind a proxy](https://matomo.org/faq/how-to-install/faq_98/)
* `DNT` – used to detect whether a visitor’s device is opted-out from tracking ([Matomo privacy](https://matomo.org/faq/general/configure-privacy-settings-in-matomo/))