Understanding the Jekyll Build Process

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You've seen all the files and folders in a Jekyll project, but have you ever wondered how they all come together to form a final website? The magic happens when you run the build command. Jekyll, as a static site generator, is a program that takes your source files and compiles them into a complete, static website. This process is a straightforward, step-by-step conversion from your raw content and templates into pure HTML, CSS, and JavaScript. Understanding this workflow is essential because it helps you debug problems and make sure your files are in the right places. Let's walk through the journey of a file, from its initial creation to its final form in your live website.

The entire build process is designed to be automated and predictable. Jekyll follows a set of internal rules that govern how it handles each file type and folder. It knows which files to process, which ones to copy directly, and which ones to ignore completely. This predictable workflow is what makes Jekyll so efficient. Instead of manually converting every single Markdown file or copying every image, you just run one command, and Jekyll handles all the details for you. This allows you to focus on your content and design, not on the tedious technical work. The result is a fast, secure, and easy-to-manage website that is perfect for GitHub Pages.

Table of Contents

Step 1 The Configuration and Setup

The very first thing Jekyll does when you run the build command is read your _config.yml file. This file is the instruction manual for the entire build. Jekyll uses it to get all the global settings for your site, such as the title, description, and base URL. It also checks for any permalink settings, which will determine the URL structure for all your blog posts. Any plugins you have listed in your Gemfile and configured in _config.yml are loaded at this stage. This initial step is critical because it sets the stage for how all the other files will be processed. Think of it as Jekyll getting its marching orders before it starts working on your content.

Step 2 The Content Engine at Work

Processing Your Posts and Pages

After loading the configuration, Jekyll starts looking for content. It first scans your project for files that need to be processed. This includes all the Markdown and HTML files in your root directory (your pages) and all the Markdown files in your _posts directory (your blog posts). For each of these files, Jekyll reads the YAML front matter at the top. This is the block of metadata that you enclose with three hyphens. The front matter contains important information like the title of the page and, most importantly, which layout to use.

For files in the _posts folder, Jekyll also uses the filename itself to gather information. It extracts the date from the YYYY-MM-DD part of the name and the URL slug from the title part. This is how Jekyll automatically creates a timeline for your blog posts. It processes each file, converting the Markdown into HTML, but it's not a complete HTML page yet. The processed content is just a piece of the puzzle that is about to be placed into a template.

How Front Matter and Layouts Connect

This is where the magic of Jekyll's templating system comes in. For each processed file, Jekyll looks at the layout variable you specified in the front matter. It then finds the corresponding HTML template in your _layouts directory. For example, if you have layout: post in your front matter, Jekyll will find the post.html file in the _layouts folder. It then takes the HTML content it generated from your Markdown file and inserts it into the template. The template itself might have special Liquid tags like {{ content }}, which act as a placeholder for your content. This is how your raw Markdown text is transformed into a fully styled HTML page with a header, footer, and navigation bar.

An Example of Content Insertion

Imagine your post.html layout file contains HTML for a header and a footer, with a line in the middle that says <main>{{ content }}</main>. Jekyll will take the HTML it generated from your post's Markdown file and replace the {{ content }} tag with that HTML. The result is a complete HTML file that has both your custom design and your content.

Step 3 The Design Layer

At the same time Jekyll is processing your content, it's also handling all your other design files. If you have any Sass files in your _sass directory, Jekyll will compile them into a single CSS file. It also copies all of your static assets—images, JavaScript, and any other files that don't start with an underscore—to the final output directory. This is why it's so important to keep these files in a dedicated folder like assets. Jekyll won't process them, but it will make sure they are available in the final website with their original file structure intact. For example, a file at assets/images/logo.png in your source folder will be copied to the exact same path in the final output.

This step also includes processing any includes that you have in your layouts. When Jekyll is building a layout, it will find any Liquid include tags, such as {% include header.html %}, and replace them with the actual content of the file from your _includes directory. This modular approach ensures that your final HTML files are complete and ready to go.

Step 4 The Final Output Folder

After all the processing is complete, Jekyll puts the entire, finished website into a directory named _site. This is the final stage of the build process. The _site folder contains a complete, self-contained static website. It has all the HTML files for your posts and pages, all your CSS and JavaScript files, and all your images, all linked together correctly. This folder is the final product that gets published to GitHub Pages or any other web server. It's crucial to understand that the _site folder is an output and is completely temporary. You should never edit anything inside it directly because it gets deleted and rebuilt from scratch every time you run the build command. By knowing this process, you can work on your source files with confidence, knowing that Jekyll will handle the final conversion for you.

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