Custom theme, part 2: Two ways of building WordPress themes

There are basically two big approaches to building WordPress themes:

1. 🧓 Classic (PHP template-based themes)

2. 🆕 Modern (Block / Full Site Editing themes with HTML templates)

Let’s break them down properly.

1️⃣ Classic WordPress Theme (PHP Template System)

This is the “old-school” but still very widely used method.

Structure

A classic theme consists of PHP files like:

style.css
index.php
header.php
footer.php
sidebar.php
functions.php
single.php
page.php
archive.php

🔧 How it works

• WordPress uses Template Hierarchy

• It loads different PHP files depending on the request:

  • single.php → blog post

  • page.php → page

  • archive.php → category/archive

• You split layout into parts:

  <?php get_header(); ?>
  <?php get_footer(); ?>
  

Each part is a PHP file.

💡 What you build with

• PHP (core logic)

• HTML

• CSS

• JS

• WordPress hooks (add_action, add_filter)

• Template tags (the_title(), the_content())

✅ Pros

• Full control

• Mature ecosystem

• Tons of tutorials

• Perfect if you like backend logic (you probably would 👀)

❌ Cons

• Mixing PHP + HTML can get messy

• Harder for non-devs to edit layouts

• Less visual editing

2️⃣ Modern WordPress Theme (Block / FSE Theme)

This is the new approach introduced with Full Site Editing in WordPress 5.9+.

Instead of PHP templates, you build themes with:

• HTML template files

• Block JSON config

• Reusable block components

Structure

Typical structure:

style.css
theme.json
templates/
  index.html
  single.html
  page.html
parts/
  header.html
  footer.html

Notice something?

👉 Templates are .html, not .php.

🔥 How it works

Instead of PHP functions like:

<?php the_content(); ?>

You use block markup:

<!-- wp:post-content /-->

Everything is a block.

Header, footer, query loops — all blocks.

WordPress parses this block HTML and renders it dynamically.

🧠 Core idea

Layout = Blocks
Design system = theme.json
Templates = HTML with block markup

You don’t write PHP for layout anymore.

💡 What you build with

• HTML

• Block comments (<!-- wp:... -->)

• theme.json (design system)

• Optional custom blocks (React if advanced)

✅ Pros

• Cleaner separation of structure & logic

• Visual editing in admin

• Reusable block patterns

• Future direction of WordPress

❌ Cons

• Less raw control than classic PHP

• More abstract

• Can feel “magical”

• Still evolving ecosystem

🆚 Side-by-Side Comparison

🧠 Which One Should You Care About?

Since you’re a developer who likes structure and control:

• If you want deep backend logic and customization → Classic PHP themes

• If you want modern architecture & product-oriented flexibility → Block themes