Angular: Slice pipe not giving expected result

I'm using Angular 6 with angular instantsearch. Inside an overview of my results I want to print a "description"-property of my results, but just the first 500 letters. For that purpose I want to use the built-in slice pipe.

I think I use it as described in the official Angular API but the description is still shown as the full text, not sliced at all. Do you have any ideas?

The code looks like this:

<div fxLayout="column" fxLayoutAlign="start start" fxLayoutGap="5px">
            <ais-highlight attribute="description" [hit]="hit">
              <p>{{ hit.description | slice:0:100 }}</p>
            </ais-highlight>
            <button mat-stroked-button color="accent" (click)="projectDetail(hit.id)">Projekt anzeigen</button>
</div>

Thanks in advance!