Helpers & filters

Helpers are functions accessible from pages and layouts that help to render the content.


There are different types of helpers, the most common type is a filter, used to transform values. Some template engines, like Nunjucks, have several builtin filters, but you can add more:

// Filter to convert a string to uppercase
site.filter("uppercase", (value) => value.toUpperCase());

Now, use it in your templates:

<h1>{{ title | uppercase }}</h1>

If your filter is asynchronous, set true as the third argument:

site.filter("async_filter", async (value) => value, true);

Not all template engines support async filters.

Builtin filters

Lume includes the following convenient pre-installed filters:

  • md: Allows to render Markdown content to HTML. More info
  • njk: Allows to render Nunjucks content to HTML. More info
  • url / htmlUrl: Allows to normalize URLs. More info


Some templates engines allows to add other helpers different to filters, like custom tags. To configure that, there's the helper() method that allows to add any generic helper.

site.helper("uppercase", (text) => text.toUpperCase(), { type: "tag" });

The third argument is an object with different properties:

  • type: The type of helper. It can be tag, filter or any other, depending on the template engine.
  • async: Set true to configure the helper as async.
  • body: Set true to configure that the helper accept a body (supported only by nunjucks custom tags)

Example of custom tag with body:

site.helper("uppercase", (body) => body.toUpperCase(), {
  type: "tag",
  body: "true",

Note: The method filter() is just a shortcut of helper() with { type: "filter" }.