What Changed and Why It Matters
WordPress has been moving in one direction since 2018: blocks everywhere. Full Site Editing (FSE) is the result of that push. It extends the block editor beyond your content area to cover your entire site layout, including the header, footer, sidebars, and page templates.
This is not a minor update to how themes work. It changes the tools you use to customize a site, where those tools live, and what kind of theme you need to use them. If you built your site on a classic theme and have been watching from the sidelines, this post explains what FSE actually is, what block themes offer compared to classic themes, and how to decide whether switching makes sense for your situation.
This post is written for site owners who work inside the WordPress admin, not for developers. If you use a theme from a shop or the WordPress.org directory and customize through menus and settings panels, this is for you.
Classic Themes vs. Block Themes: The Core Difference
Classic themes control your site layout through PHP template files. Your header, footer, sidebar, and page structure are defined in code. You customize the look through the Customizer (Appearance → Customize) or built-in admin panel (Redux); which gives you settings panels for colors, fonts, logo, menus, and so on. Widgets go into widget areas. Child themes let you override parent theme files without editing the original.
Block themes replace PHP templates with HTML template files. Instead of the Customizer, you get the Site Editor (Appearance → Editor), where you edit your header, footer, and page templates visually using blocks, the same way you edit a post. A file called theme.json handles global design settings like colors, typography, and spacing. No PHP knowledge is needed to change your layout.
What stays the same: the block editor for your content, plugins, custom fields (including ACF), and menus. Switching to a block theme does not break your content or your plugin functionality in most cases, though some plugins are designed with classic themes in mind.
| Feature | Classic Theme | Block Theme |
|---|---|---|
| Template editing | Edit PHP files (or child theme) | Edit visually in Site Editor |
| Global styles | Customizer panels | theme.json + Site Editor |
| Header/footer changes | PHP template or widget area | Site Editor, no code needed |
| Customization method | Settings panels, CSS | Block editing, theme.json |
| Learning curve | Familiar if you’ve used WordPress 4.x+ | New workflow, new mental model |
The Building Blocks of a Block Theme
A block theme is made up of several distinct pieces. You do not need to edit any of them directly, but knowing what each one does helps you understand what you are looking at inside the Site Editor.
theme.json is a configuration file that ships with the theme. It defines your site’s design: the color palette, font sizes, spacing options, and which block features are turned on or off. When you change global typography or pick a color in the Site Editor, those choices interact with what theme.json has defined. Think of it as the design rulebook for the whole site.
Template files are HTML files that control the layout of different page types: single posts, archive pages, the 404 page, search results, and so on. Each template is made up of blocks. You can edit these templates visually in the Site Editor without touching the underlying file.
Template parts are reusable sections of a template, typically the header and footer. A template part sits inside multiple templates so an edit to the header propagates everywhere it appears.
Patterns are pre-built block layouts, like a hero section, a features grid, or a testimonials block. Themes ship patterns you can insert into your pages or templates and then customize. They save setup time compared to building a layout from scratch.
The Site Editor is where all of the above comes together. From there you can edit templates, template parts, patterns, and global styles in a single interface.
What You Can Do in the Site Editor
The most immediate change block themes bring is editing your header and footer directly. In a classic theme, changing your header usually means either adjusting a limited set of Customizer options or editing a PHP file. In the Site Editor, you click into the header, move blocks around, add or remove elements, and save. The same applies to the footer.
Templates can be assigned per post type, per category, or per individual post. If you want your blog posts to use a different layout than your portfolio pages, you create separate templates and assign them. You do not need a plugin to do this.
Global styles let you change typography, colors, and spacing across the whole site from one panel. You adjust the body font and every text element that inherits it updates. This replaces a lot of what you previously did through the Customizer or by adding CSS.
Style variations are a feature some themes include. They are complete design presets, different color and typography combinations, that you switch between in one click. Not every theme ships with them, but when they are available, you can change the overall look of the site without any CSS.
What still requires code: custom functionality like booking systems, membership logic, or non-standard admin interfaces still depends on plugins or custom development. The Site Editor does not replace PHP for functionality, only for layout.
theme.json: Why It’s the Heart of a Block Theme
In a classic theme, design settings are scattered. The Customizer holds some, a stylesheet holds others, and sometimes an options panel holds the rest. In a block theme, theme.json centralizes all of that into one place.
From a site owner’s perspective, you will rarely open theme.json directly. What it does is set the boundaries and defaults for what you can change in the Site Editor. If your theme defines five font families in theme.json, those are the five you see in the typography panel. If your theme defines eight colors in the palette, those are the eight colors available when you style a block.
theme.json effectively replaces most of what the Customizer handled: default colors, font sizes, button styles, spacing scale. The trade-off is that theme.json is less visual than a settings panel. If you want to change something that theme.json controls and the Site Editor does not expose a setting for it, you are back to needing a developer or a child theme.
Block Theme Patterns
Patterns are pre-assembled block layouts you can insert into any page or template. A theme might ship a pattern for a two-column feature section, a full-width hero, or a footer with three widget columns. You insert a pattern, then edit the text and images to fit your content.
Patterns come in two types. Synced patterns (previously called reusable blocks) work like a shared component: if you edit the pattern in one place, the change appears everywhere it is used. Unsynced patterns are inserted as a one-off copy. Once inserted, editing that instance does not affect other uses of the same pattern.
When a theme ships patterns, it usually includes the building blocks for common page types. This reduces the manual block work needed to produce a professional layout. The practical limitation is that patterns only cover what the theme author anticipated. If you need a layout the theme did not include, you build it yourself or find a pattern from another source.
Limitations and Honest Trade-offs
The Site Editor is not finished software. Usability has improved since FSE launched in WordPress 5.9, but the interface is still more complex than the Customizer for straightforward tasks like swapping a logo or changing a menu. If you are used to a clean settings panel for those actions, the Site Editor will feel indirect at first.
Some plugins still expect a classic theme structure. Plugins that add widget areas, integrate with the Customizer, or hook into PHP template actions may not work as intended with a block theme. This is not universal, but it is worth checking your specific plugins before switching.
Certain customizations that were straightforward in a classic theme, like adding a custom sidebar to specific pages or controlling ad placement in content, can require more steps in a block theme depending on what the theme supports. The “no PHP required” promise is accurate for layout, not for everything.
A classic theme may still be the right choice if you have an existing site that works, you rely on a page builder like Elementor or Divi, your setup depends on plugins with known FSE incompatibilities, or your design requirements go beyond what the Site Editor exposes. Switching to a block theme carries real migration overhead and should not be treated as automatic.
Is a Block Theme Right for Your Site?
Block themes suit some situations clearly and others less so.
Good fit:
- New sites with no existing setup to migrate
- Sites where you want to control layout without writing CSS
- Users already comfortable with the Gutenberg block editor
- Projects where you want visual header/footer editing without a plugin
Less ideal fit:
- Sites built around Elementor, Divi, or Beaver Builder workflows
- Sites with heavy reliance on classic widgets or the Customizer
- Projects with legacy plugins that do not support FSE
- Admin setups that depend on PHP template hooks for functionality
A short checklist before deciding:
- Are your current plugins listed as compatible with block themes?
- Do you use a page builder for layout? (If yes, FSE duplicates much of what you already have.)
- Are you building from scratch or migrating an existing site?
- Is your current theme still receiving updates and security fixes?
- Do you want visual control over the header and footer without a plugin?
How to Get Started
Block themes are available in the WordPress.org theme directory under the “Block themes” filter. Commercial theme shops also publish block themes, often with more refined design and support than free alternatives.
Once you activate a block theme, find the Site Editor at Appearance → Editor. The first time you open it, you will see your site’s live template with the editing tools on the left.
Recommended first steps after activating a block theme:
- Open the Site Editor and review the default templates. Check how the single post, archive, and homepage templates are built.
- Go to Styles (the circle icon in the top right of the Site Editor) and review the global typography and color settings.
- Edit the header template part first since it appears on every page.
- Test your key plugins to confirm they work as expected under the new theme.
- Check your menus. Block themes handle navigation through a Navigation block, which works differently from the classic Appearance → Menus screen.
My Take:
Block themes are not a trend WordPress is testing. FSE is the direction the platform has committed to, and the tooling will continue to develop around it. Understanding how block themes work, what the Site Editor can do, and where the current limits are gives you a clearer picture of what you are buying into before you activate one. That clarity is more useful than either enthusiasm or skepticism on its own.
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