WordPress Development
WordPress Full Site Editing: Block Themes, Site Editor, and theme.json Explained
Full Site Editing is the most significant change to WordPress in its history. Here is everything you need to understand — from block themes to template parts to theme.json.
Full Site Editing (FSE) is the most significant change to WordPress in its history. It extends the Gutenberg block editor from controlling post and page content to controlling every part of the site: headers, footers, sidebars, single post templates, archive pages, and the global design system. Understanding FSE is now essential for professional WordPress development.
What Full Site Editing changes about WordPress
Before FSE, WordPress separated content (managed in the post editor) from design (managed in the Customiser, widget areas, and PHP template files). FSE collapses this distinction — everything is blocks, everything is editable in one visual interface.
| Feature | Before FSE | With FSE |
|---|---|---|
| Headers and footers | Edited in PHP template files or Customiser | Visual block editor in Site Editor |
| Sidebar widgets | Widgets screen with limited layout control | Block-based widget areas with full Gutenberg blocks |
| Single post template | single.php in theme files | Visual template editor in Site Editor |
| Archive pages | archive.php, category.php in theme files | Visual template editor in Site Editor |
| Global styles (colours, fonts) | Theme options or Customiser | Global Styles panel in Site Editor |
| Template parts (shared sections) | Included PHP files | Reusable block template parts |
| Theme requirement | Classic PHP-based themes | Block themes with theme.json configuration |
Block themes — the FSE requirement
FSE requires a block theme — a theme built specifically for Full Site Editing. Classic themes (Astra, Kadence, GeneratePress in their traditional forms) do not support FSE’s Site Editor. Block theme examples:
WordPress continues to fully support classic themes. FSE does not replace classic theme development — it adds a new, more visual approach. For existing sites on Astra, GeneratePress, or Kadence classic themes, there is no pressure to migrate. Adopt FSE for new projects where the block-based workflow fits.
Navigating the Site Editor
Access the Site Editor via Appearance › Editor (replaces Appearance › Customise on block themes). The Site Editor interface has four main sections:
- Templates: manage all page templates — Single Post, Front Page, Archive, Search, 404, and any custom templates you create.
- Template Parts: reusable sections shared across templates — Header, Footer, Comments section. Edit once, updated everywhere it is used.
- Global Styles: site-wide typography, colour palette, spacing, and block default styles. Changes here affect every page without touching individual blocks.
- Navigation: visual navigation menu editor integrated directly into the Site Editor.
theme.json — the configuration backbone
Every block theme includes a theme.json file that defines the design system: colour palette, typography scale, spacing scale, and which design controls are exposed to users. Understanding theme.json is essential for customising block themes:
- Colours defined in theme.json appear in the Global Styles colour palette and in every block colour picker
- Font families defined in theme.json are available in every block typography setting
- The settings section controls which options are exposed to editors — you can disable specific controls to simplify the editing experience for clients
- Child themes override parent theme.json settings by creating their own theme.json with only the values they want to change
Block patterns — reusable section designs
Block patterns are pre-designed groups of blocks that can be inserted into any template or post with one click. They are the FSE equivalent of Elementor template sections or Kadence pattern library.
- WordPress.org has a public Block Pattern Library at wordpress.org/patterns with hundreds of free patterns
- Your theme includes its own patterns — accessible via the Patterns panel in the Site Editor or via the / command in the post editor
- Create your own patterns: design a section in the editor, select all blocks, right-click and Create Pattern. It becomes reusable across your site.
- Synced patterns (formerly Reusable Blocks) update across all instances when edited. Unsynced patterns are independent copies. Use synced patterns for footers and CTAs that appear repeatedly.
FSE vs Elementor Pro — choosing for new projects
For new WordPress projects in 2026, the choice between FSE and Elementor is a genuine architectural decision:
| Factor | FSE (block theme) | Elementor Pro |
|---|---|---|
| Performance | Better — no Elementor JS/CSS overhead | Good with optimisation |
| Design control | Good and improving rapidly | More granular — pixel-level control |
| Learning curve | Steeper — new concepts (theme.json, template parts) | Gentler — familiar visual panel |
| Future direction | WordPress native — aligned with core direction | Plugin dependency |
| WooCommerce builder | Via Woo blocks (improving) | Elementor Pro WooCommerce templates |
| Client editing experience | Clean, integrated | More widgets but more complex |
WordPress core investment is in FSE. Block themes will become the standard.
For projects where design complexity is moderate, performance is paramount, or you want alignment with where WordPress is heading, choose a block theme and FSE. For highly visual marketing sites, WooCommerce stores needing custom product templates, or clients needing the richer Elementor widget library, Elementor Pro remains the more capable tool today.
Need a WordPress site built with Full Site Editing or Elementor?
Simple Automation Solutions builds on both block themes (FSE) and Elementor Pro — choosing the right architecture for each project for businesses worldwide.
Frequently asked questions
Can I convert my existing classic theme WordPress site to Full Site Editing?+
Migration from a classic theme to a block theme is a significant project, not a simple upgrade. You would need to choose a new block theme, recreate your design in block-based templates, and potentially rebuild page layouts that relied on Elementor or classic theme features. For most established sites, the disruption of migration outweighs the benefits unless you have a specific reason to move to FSE (performance requirements, developer preference, or a major redesign project that warrants rebuilding anyway).
Are block themes slower than classic themes?+
No — block themes are typically faster. They carry significantly less CSS and JavaScript overhead than themes paired with Elementor or other page builders. A block theme with only WordPress core blocks and well-optimised theme.json configuration consistently scores better on Core Web Vitals than equivalent Elementor-based builds. The performance advantage is one of the primary reasons developers are adopting FSE for new projects.
What happens to the WordPress Customiser with Full Site Editing?+
On block themes, the Customiser is replaced by the Site Editor. The Customiser still appears in the admin menu but shows a limited set of options (or nothing, depending on the theme). On classic themes, the Customiser continues to function exactly as before. WordPress has committed to maintaining Customiser support for classic themes for the foreseeable future — FSE does not break existing sites.
