website/_includes/debug/url.html

{% assign shouldRender = false %}

{% if jekyll.environment == "development" %}
  {% assign shouldRender = true %}
{% endif %}

{% if include.forceRender %}
  {% assign shouldRender = true %}
{% endif %}

{% if shouldRender %}
  {% if include.url contains "_" %}
    <div class="alert alert-danger">
      <h4>Yarn Website Internal Developer Info!</h4>

      <p>
        This page has an incorrectly formatted url. Underscores (_) are not
        allowed inside urls, use dashes instead.
      </p>

      <pre><code>{{include.url}}</code></pre>

      <p>
        If you believe you are seeing this warning by mistake, please open
        an issue.
      </p>
    </div>
  {% endif %}
{% endif %}