# Dialogflow: Events
Use events to trigger Dialogflow intents.
Aside from user input, events are also used to trigger intents. Any intents with the event name listed under the “Events” section will be triggered when an event occurs.
A good example of this is the default `WELCOME` event, which is already built into Dialogflow. This event is triggered whenever a new user begins chatting with the bot.
### Parametric URLs
Any intents with the events for `REF_[PARAM]` or `REF_START_[PARAM]` are triggered when the user arrives from a parametric URL.
**Example:** m.me/respondio?ref=\[PARAM].
If you would like a custom parameter to trigger a Dialogflow intent, please ensure the parameter has a prefix of `REF_` on the intent's event configuration. Example: `REF_PARAM`
Referring to the example above, if you want to trigger an intent from m.me/respondio?ref=medium , add `REF_MEDIUM` to the intent's event configuration.
{% hint style="info" %}
Bear in mind that the `REF` prefix is not necessary for the `WELCOME` event as this event is a default event built into Dialogflow.
{% endhint %}
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