Title: Headline Testing network calls
Author: elenadosil
Published: February 11, 2026

---

 1. [Troubleshooting common issues](https://docs.parse.ly/troubleshooting-issues/)
 2. Headline Testing network calls

#  Headline Testing network calls

Use browser DevTools to verify [Headline Testing](https://docs.parse.ly/user-handbook/dashboard/optimization-menu/headline-testing-tab/)
is functioning correctly or to troubleshoot issues with a test.

**Prerequisites**

 * [An active headline test configured for the page](https://docs.parse.ly/user-handbook/dashboard/optimization-menu/headline-testing-tab/create-test/)
 * [The Headline Testing script installed on the site ](https://docs.parse.ly/installation-resources/add-on-features/install-headline-testing/)
 * Browser DevTools open before loading the page

## How to view network calls

 1. Open browser DevTools (F12 or right-click > Inspect).
 2. Select the **Network** tab.
 3. Filter by “parsely” to isolate relevant requests.
 4. Load or refresh the page containing the headline test.

## Check network calls during a test

When a headline test is functioning correctly, the browser makes several network
calls. The first call, on the homepage, loads the `vip-experiments.js` script. Without
this call, the test does not function.

[⌊Browser DevTools Network tab filtered by parsely, showing the vip-experiments.
js script request highlighted with a red annotation indicating the script is being
loaded⌉⌊Browser DevTools Network tab filtered by parsely, showing the vip-experiments.
js script request highlighted with a red annotation indicating the script is being
loaded⌉[

Next, still on the homepage, a `tr?experiment_id` call fires with an `impression`
event type.

[⌊Browser DevTools Network tab showing a tr?experiment_id request selected, with
the Payload panel displaying event_type as impression⌉⌊Browser DevTools Network 
tab showing a tr?experiment_id request selected, with the Payload panel displaying
event_type as impression⌉[

After a visitor clicks the article being tested, another `tr?experiment_id` call
fires with a `click` event type.

[⌊Browser DevTools Network tab showing a tr?experiment_id request selected, with
the Payload panel displaying event_type as click⌉⌊Browser DevTools Network tab showing
a tr?experiment_id request selected, with the Payload panel displaying event_type
as click⌉[

## Troubleshooting

 * **The `vip-experiments.js` script does not load:** Verify the headline test is
   active and that the script has been correctly added. For SPA or pages loading
   dynamically, enable the `enableLiveUpdates` option. See [Install Headline Testing: Live Updates](https://docs.parse.ly/installation-resources/add-on-features/install-headline-testing/#:~:text=Copy-,Live%20Updates,-By%20default%2C%20headlines)
   for configuration details.
 * **The `impression` or `click` events do not fire:** Confirm the `vip-experiments.
   js` script has been loaded.

Last updated: February 11, 2026