# How to find the backend domain/URI for RUM application detection rules **URL:** \ **Category:** Troubleshooting\ **Tags:** real-user-monitoring-classic, application-detection\ **Created:** [November 16, 2023, 5:57pm UTC](https://community.dynatrace.com/t/how-to-find-the-backend-domain-uri-for-rum-application-detection-rules/42302 "2023-11-16T17:57:49Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![AdamPiotrowicz](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@AdamPiotrowicz](https://community.dynatrace.com/u/AdamPiotrowicz)\ **Post date:** [November 16, 2023, 5:57pm UTC](https://community.dynatrace.com/t/how-to-find-the-backend-domain-uri-for-rum-application-detection-rules/42302/1 "2023-11-16T17:57:49Z")
# Summary Application detection rules are evaluated by OneAgent on the first instrumented tier of your application. See [How does Dynatrace apply your application detection rules?](https://docs.dynatrace.com/docs/platform-modules/digital-experience/web-applications/initial-setup/define-your-applications-via-the-my-web-application-placeholder#rum-appdetection-appparam) for more details. # Problem In some cases, an uninstrumented component, such as a reverse proxy or a load balancer, is between the browser and the first instrumented tier of your application and rewrites the URL. As a result, the URL used for application detection differs from the URL that was originally requested by the browser. In this scenario, we cannot use the URL we see in the web browser and test it in the detection rules checker (_Settings_ → _Web and mobile monitoring_ → _Application detection_). Instead, we have to find the **related server-side URL**  that is available in Trace / PurePath, under _Host_ and _URI_ fields. # Resolution Below is short video showing how to easily find the _Host_ and _URI_ field values from Trace / PurePath that are associated with the default _My web application:_ https://play.vidyard.com/cBhkXSCanqy5TUhB5e9mgP.html?autoplay=0 **Note:**  If you find in Trace / PurePath other fields with domains (i.e. _X-Forwarded-For_), check the _Settings_ → _Web and mobile monitoring_ → _Host name determination_ configuration, since the order matters and other field values might be taken into consideration. # What’s next If this article did not help, please open a support ticket, mention that this article was used and provide the following in the ticket: - link problematic RUM application, - information about the detection rule you believe works incorrectly.