Truncates a value to n characters and appends an ellipsis (…). It does not count HTML tags as characters and closes any tags that were left open as a result of the truncation.
Variable
blurb = '<p>You are <em>pretty</em> smart!</p>'
Template
{{ blurb|truncatechars_html:15 }}
Result
<p>You are <em>pretty…</em></p>
Autoescaping
Be aware that autoescaping is on by default in Django. If you do not turn it off, either with the {% autoescape off %} tag or the safe filter, the HTML will be escaped.
The easiest way to avoid this is to chain on the safe filter:
{{ blurb|truncatechars_html:15|safe }}

Commentary
If you do not want to break off in the middle of a word, use
truncatewords_htmlinstead.