Jekyll Related Posts without Plugin

gistfile1.txt

{% assign hasSimilar = '' %}
{% for post in site.related_posts %}
    {% assign postHasSimilar = false %}
    {% for tag in post.tags %}
        {% for thisTag in page.tags %}
            {% if postHasSimilar == false and hasSimilar.size < 6 and post != page and tag == thisTag %}
                {% if hasSimilar.size == 0 %}
                <h4>Similar Posts</h4>
                <ul>
                {% endif %}
                <li class="relatedPost">
                    <a href="{{ site.url }}{{ post.url }}">{{ post.title }}
                    {% if post.series %}
                        (Series: {{ post.series }})
                    {% endif %}
                    </a>
                </li>
                {% capture hasSimilar %}{{ hasSimilar }}*{% endcapture %}
                {% assign postHasSimilar = true %}
            {% endif %}
        {% endfor %}
    {% endfor %}
{% endfor %}
{% if hasSimilar.size > 0 %}
    </ul>
{% endif %}