Collections: Tags, Categories, and Custom Taxonomies

  1. Overview
  2. Tags and Categories
  3. Custom Taxonomies
  4. The collections object


JS.SSG has out-of-the box for two taxonomies: tags and categories. These are set in the frontmatter of your content files, and populate the site.collections data that is passed as a prop to every layout.

You can also create custom taxonomies by declaring them in the config file.

Tags and Categories

Tags and categorie are useful for organising the data in site. These can be set using the tags and categories frontmatter keys in markdown files.

title: An example blog post
tags: [foo, bar, baz]

Ullamco tempor ad dolore ad consequat sint nulla et dolore proident elit nostrud.

tags and categories (and custom taxonomies) can accept either a single string value or an array of strings. Both tags: foo and tags: [ foo, bar] are valid.

If either tags or categories are set in a page's frontmatter, that page will be added to the relevant "collection" when JS.SSG compiles your site. You can use these collections within template files (to create menus, lists of posts, index pages, etc.) by accessing the site.collections object. See The collections object section of this page for more details.

Custom Taxonomies

If tags and categories are too restrictive for your needs, you can create additional taxonomies using the collections configuration value.

// config.json
    "collections": ["customTaxonomyOne", "customTaxonomyTwo"]

These taxonomies will then be available to use within your content's frontmatter in the same manner as tags and categories and JS.SSG will use these when creating collections.

title: An example blog post
customTaxonomyOne: [foo, bar, baz]

Ullamco tempor ad dolore ad consequat sint nulla et dolore proident elit nostrud.

The default taxonomies of tags and categories will always be available regardless of the contents of config.collections, so you don't need to re-declare them when declaring new custom taxonomies.

By convention, JS.SSG uses plurals for the taxonomy slugs. For example, tags rather than tag.

The collections object

Information about all taxonomies is available with templates via the site.collections object. The collections data has two sections: site.collections.keys and site.collections.pages.


site.collections.keys provides an object where the keys are the slugs for all the available taxonomies and the values are an array of all the items within that taxonomy. This is made available so you can have easy access to all the taxonomy keys without having to reverse-engineer them from the collections.pages data.

For example, if you used two tags within your content, tags: video and tags: image, then the collections.keys data would appear like this:

keys: {
    categories: [],
    tags: [ 'video', 'image' ]


site.collections.pages is where the page data for all collections is stored. Assuming the previously used example of two tags, video and image, the pages data would look something like this:

pages: {
    categories: {},
    tags: {
        video: [
            { page data }
        image: [
            { page data },
            { page data },

The page data objects have the following values:

  • type - the filetype for the content file (either 'md', or 'mdx'.
  • frontmatter - an object containing all the pages frontmatter, including title, layout, tags, etc.
  • markdown - the raw markdown content of the page, as a string.
  • filePath - the full path to the orginial markdown file on disk (useful for debugging).
  • url - the relative URL of the page in the final build.