How to check if a field has more than one value I am working on a field template to display images in a carousel (I'm using BootStrap). My field is named “galerie”
I copied field.html.twig from the core and saved it as field--field-galerie.html.twig
I managed successfuly to add the necessary markup for BootStrap carousel to work.

The wrapping markup displaying the carousel and its control shows up when there is only one image. I thought it would not. It opens after a {% if multiple %} condition and closes before the {% else %}.
My understanding is that {% if multiple %} only checks if the field is set to accept multiple values.  

I don't know how to write an condition in twig checking if the field contains one image or more, to trigger (or not) the carousel thingee.
Use the length filter, which also works on arrays:

{% if items|length &gt; 1 %}
  field contains more than 1 item
{% endif %}