HTML files are pre-processed by default as Liquid templates. This is an optional feature and can be changed to a different template engine of your choice or disabled entirely. Furthermore, it can be configured on a per-template basis or globally. Read more at Changing a Template’s Rendering Engine.

{% callout "pitfall" %}This is a Common Pitfall.{% endcallout %}

Take care with the HTML template type when using the same --input and --output directory (this is not the default).

If you run Eleventy more than once, it’ll try to process your output files too which may result in duplicate template errors.

{%- set codeBlock %}{% raw %} $ npx @11ty/eleventy --input=. --output=. --formats=md,html Writing ./README/index.html from ./README.md

$ npx @11ty/eleventy --input=. --output=. --formats=md,html {% endraw %}{%- endset %} {{ codeBlock | highlight("bash") | safe }}

The second run will attempt to write ./README/index.html from both ./README.md and ./README/index.html, resulting in a Duplicate Permalink Error (two templates writing to the same location). You can workaround this issue using the Ignores feature.

If you’re going to use --formats=html, it’s probably best not using the same input and output directories.