Jekyll’s site.url and baseurl

Jekyll’s site url and baseurl variables cause a lot of confusion for users. I see it all the time in the Jekyll Talk forum, Stackoverflow, or as bug reports in my themes.

My Jekyll site works locally but when I push it up to GitHub Pages it is broken with no styling and looks like this. Help!"

What are url and baseurl?

So what exactly are the url and baseurl variables? To start, both are site-wide variables set in the _config.yml file and affect how Jekyll builds URLs. I like to describe them like this:

How to use url and baseurl

A couple of important facts to keep in mind when using both:

1. Leave off trailing forward slashes when setting url

   ✅ Do this	❌ Don’t do this
   url: https://mademistakes.com	url: https://mademistakes.com/

2. baseurl is not needed for most sites and can be omitted.
3. baseurl is only necessary when hosting your site in a sub-directory. Project sites hosted on GitHub Pages are the common use-case of this variable.

Jekyll URL troubleshooting

If we go back to the example above with the broken CSS link and inspect the HTML’s source. You will often find that the link to the CSS file is incorrect for any number of reasons:

1. Double forward slashes e.g., //minima/assets/style.css
2. Missing base URL due to not using relative_url filter, absolute_url filter, or {{ site.baseurl }} in theme files.

Jekyll development and site.url

One other question I see asked over and over again from Jekyll users is:

Why are my links broken? They all start with http://localhost:4000 or http://127.0.0.1:4000.

This happens because in older versions of Jekyll (v3.3 through 4.1) it would reset site.url to localhost:4000 when JEKYLL_ENV=development (the default environment value), overriding whatever is set in the _config.yml. In newer versions of Jekyll (v4.2 and up) this reset of site.url no longer happens.

In older versions of Jekyll, site.url is also reset to http://localhost:4000 when spinning up a development server with the jekyll serve command.

site.url values

Under normal circumstances these two conditions won’t cause any headaches, especially when hosting on GitHub Pages as the environment and url are set automatically.

The issue surfaces when building locally, using an older versions of Jekyll, and then forgetting to set JEKYLL_ENV to production. Or pushing up files from a _site directory after running jekyll serve instead of jekyll build.

Examples

Below you will find examples of how to write different types of links that require site.url or site.baseurl values to work properly. Links marked as ✅ have valid URLs while those marked as ❌ are broken and will trigger a 404 file not found error.

Each of the examples assume:

1. Jekyll v4.2 or greater is installed.
2. The site is hosted on GitHub Pages in a sub-directory named blog.
3. Posts follow standard naming conventions of YYYY-MM-DD-filename.md inside of a _posts directory.
4. Image assets are in a images directory inside of the root.

5. Have the following _config.yml settings:

   url: https://mmistakes.github.io
   baseurl: /blog
   permalink: date

Markdown links

How to link to pages, posts, and images in Markdown.

[about page](/about.html)

[about page](/blog/about.html)
[about page]({{ site.baseurl }}/about.html)
[about page]({{ 'about.html' | relative_url }})

[Welcome to Jekyll post](/blog/2021/06/29/welcome-to-jekyll.html)
[Welcome to Jekyll post]({% post_url 2021-06-29-welcome-to-jekyll %})
[Welcome to Jekyll post]({% link _posts/2021-06-29-welcome-to-jekyll.md %})

[cheese pizza](pizza.jpg)

[cheese pizza](images/pizza.jpg)

[cheese pizza](/images/pizza.jpg)

[cheese pizza](/blog/images/pizza.jpg)
[cheese pizza]({{ '/images/pizza.jpg' | relative_url }})
[cheese pizza]({{ site.baseurl }}/images/pizza.jpg)

Root-relative URL links

How to link resources with root-relative URLs, like stylesheets, favicons, and JavaScript.

<link rel="stylesheet" href="/assets/css/style.css">

<link rel="stylesheet" href="/blog/assets/css/style.css">
<link rel="stylesheet" href="{{ site.baseurl }}/assets/css/style.css">
<link rel="stylesheet" href="{{ '/assets/css/style.css' | relative_url }}">

Absolute URL links

How to link to resources that require the full URL, like a canonical URL in the page’s <head>.

<link rel="canonical" href="{{ page.url }}">

<link rel="canonical" href="{{ page.url | absolute_url }}">
<link rel="canonical" href="{{ page.url | prepend: site.baseurl | prepend: site.url }}">
<link rel="canonical" href="{{ site.url }}{{ site.baseurl }}{{ page.url }}">

As you can see from above examples, Jekyll is flexible and allows for multiple ways of creating links. Personally I tend to lean on the relative_url and absolute_url filters as they require less typing and have some “smarts” to them.

The best option is the one that works for you!