searxng/searx/templates/search.html

<form method="post" action="">
    <input type="text" class="q" name="q" tabindex="1" autocomplete="off" {% if q %}value="{{ q }}"{% endif %}/>
    <input type="submit" value="search" />
    <p>
    {% for engine in engines %}
        {{ engine }}: <input type="checkbox" name="engine_{{ engine }}" checked="checked"/>
    {% endfor %}
    </p>
</form>