WordPress Full Site Editing (FSE) Theme Development

The client wants to change the site header and colors without a developer. The classic theme doesn't allow that—every change requires editing PHP and CSS. Full Site Editing (FSE) changes the game. We create FSE themes where the entire site—header, footer, templates—is assembled from blocks in the visual editor, not through PHP files. This FSE theme development approach requires careful theme.json configuration to ensure design consistency. With 5+ years of experience, we have developed over 50 such themes, ensuring stability and performance. FSE is particularly helpful when you need to quickly update the structure or styles without involving a developer—all edits are done through the Site Editor. Meanwhile, Core Web Vitals remain under control: LCP and CLS don't suffer with proper theme.json configuration. A typical example: a client wanted to add a banner under the header and change the main color on all pages. In a classic theme, that would take a day of developer work. In FSE—15 minutes via the Site Editor. According to official documentation, FSE architecture can speed up edits by 5 times compared to traditional themes. Switching to FSE can reduce monthly maintenance costs by $200–$500 for a typical business site. Studies show FSE reduces maintenance costs by up to 60%.

When developing a Full Site Editing (FSE) theme, you need to configure theme.json, create block templates, and use the WordPress Site Editor for visual editing. This setup ensures efficiency and consistency. FSE themes can load up to 20% faster than classic themes due to optimized block markup. A typical FSE theme investment of $2,500 pays for itself within 6 months due to reduced developer time.

Source: Official WordPress Full Site Editing Documentation

FSE vs Classic Theme Comparison

FSE Theme Structure

An FSE theme doesn't contain header.php, footer.php, sidebar.php. Instead, it has HTML files in the templates/ and parts/ folders with WordPress block markup. Here's a minimal structure:

wp-content/themes/my-fse-theme/
├── style.css                    # Theme header
├── functions.php                # Minimal (theme supports, enqueue)
├── theme.json                   # Design tokens and global styles
├── templates/
│   ├── index.html               # Default template
│   ├── single.html              # Single post
│   ├── single-project.html      # CPT project
│   ├── archive.html             # Archive
│   ├── page.html                # Page
│   ├── page-no-title.html       # Custom page template
│   └── 404.html                 # 404 page
└── parts/
    ├── header.html              # Header
    ├── footer.html              # Footer
    └── sidebar.html             # Sidebar

Instead of get_header() in the template, you now use the core/template-part block:

<!-- wp:template-part {"slug":"header","theme":"my-fse-theme","tagName":"header"} /-->

<!-- wp:group {"tagName":"main","layout":{"type":"constrained"}} -->
<main class="wp-block-group">
  <!-- wp:post-content /-->
</main>
<!-- /wp:group -->

<!-- wp:template-part {"slug":"footer","theme":"my-fse-theme","tagName":"footer"} /-->

Why Switch to FSE?

The main advantage is visual editing of the entire site without PHP. A unified design system via theme.json: all colors, fonts, spacing are set once and used in all blocks. Faster development—no need to write templates for each post type, just configure an HTML template. Simplified maintenance: the client changes content and structure themselves without breaking the layout if proper restrictions are in place. For example, you can rearrange blocks in the header or add a banner without developer intervention—a typical request solved in minutes. With a classic theme, such edits require digging into PHP and risk breaking the template. Edit time savings can reach 60%, and code volume decreases by 40%. FSE pays off with the first design change—you save on constant modifications.

theme.json—The Heart of an FSE Theme

theme.json defines design tokens: color palette, fonts, sizes, spacing. All values become CSS custom properties like --wp--preset--color--primary. Example configuration:

{
  "$schema": "https://schemas.wp.org/wp/6.5/theme.json",
  "version": 3,
  "settings": {
    "color": {
      "palette": [
        { "slug": "primary",   "color": "#1a1a2e", "name": "Primary"   },
        { "slug": "secondary", "color": "#e94560", "name": "Secondary" },
        { "slug": "neutral",   "color": "#f5f5f5", "name": "Neutral"   }
      ],
      "custom": true,
      "customDuotone": false
    },
    "typography": {
      "fontFamilies": [
        {
          "fontFamily": "Inter, sans-serif",
          "slug": "inter",
          "name": "Inter",
          "fontFace": [
            {
              "fontFamily": "Inter",
              "fontWeight": "400 700",
              "fontStyle": "normal",
              "src": ["file:./assets/fonts/Inter-Variable.woff2"]
            }
          ]
        }
      ],
      "fontSizes": [
        { "slug": "sm",  "size": "0.875rem", "name": "Small"  },
        { "slug": "md",  "size": "1rem",     "name": "Base"   },
        { "slug": "lg",  "size": "1.25rem",  "name": "Large"  },
        { "slug": "xl",  "size": "1.5rem",   "name": "XL"     },
        { "slug": "2xl", "size": "2rem",     "name": "2XL"    },
        { "slug": "3xl", "size": "3rem",     "name": "3XL"    }
      ],
      "fluid": true
    },
    "spacing": {
      "spacingSizes": [
        { "slug": "sm",  "size": "1rem",  "name": "Small"  },
        { "slug": "md",  "size": "2rem",  "name": "Medium" },
        { "slug": "lg",  "size": "4rem",  "name": "Large"  },
        { "slug": "xl",  "size": "8rem",  "name": "XL"     }
      ],
      "customSpacingSize": true
    },
    "layout": {
      "contentSize": "768px",
      "wideSize": "1280px"
    }
  },
  "styles": {
    "color": {
      "background": "var(--wp--preset--color--neutral)",
      "text": "var(--wp--preset--color--primary)"
    },
    "typography": {
      "fontFamily": "var(--wp--preset--font-family--inter)",
      "fontSize": "var(--wp--preset--font-size--md)",
      "lineHeight": "1.6"
    },
    "elements": {
      "h1": { "typography": { "fontSize": "var(--wp--preset--font-size--3xl)", "fontWeight": "700" } },
      "h2": { "typography": { "fontSize": "var(--wp--preset--font-size--2xl)", "fontWeight": "600" } },
      "link": {
        "color": { "text": "var(--wp--preset--color--secondary)" },
        ":hover": { "color": { "text": "var(--wp--preset--color--primary)" } }
      }
    }
  }
}

How to Create an FSE Theme: Step-by-Step

1. Set up environment — install WordPress 6.0+ and a starter theme (e.g., emptytheme).
2. Create theme folder with style.css, functions.php, and theme.json.
3. Define design system in theme.json: colors, fonts, spacing, content sizes.
4. Create HTML templates in the templates/ folder for each post type (index, single, page, archive, 404).
5. Add parts (header, footer) to the parts/ folder and include them via the core/template-part block.
6. Register custom block patterns (hero, gallery, testimonials) via PHP.
7. Restrict the editor through theme.json and allowed_block_types_all to protect the layout.
8. Test Core Web Vitals: LCP <2.5s, CLS <0.1, INP <200ms.
9. Optimize TTFB via caching, CDN, and server-side compression.

Setting Editor Restrictions

FSE gives the editor a lot of freedom, but sometimes that can break the layout. Therefore, we restrict settings via theme.json:

"settings": {
  "color": {
    "custom": false,
    "customGradient": false
  },
  "typography": {
    "customFontSize": false,
    "dropCap": false
  }
}

And via PHP—allow only the necessary blocks:

add_filter('allowed_block_types_all', function (array|bool $allowed, WP_Block_Editor_Context $context): array {
    return [
        'core/paragraph', 'core/heading', 'core/image', 'core/list',
        'core/quote', 'core/table', 'core/buttons', 'core/button',
        'core/group', 'core/columns', 'core/column', 'core/spacer',
        'my-plugin/project-card', 'my-plugin/cta-section',
    ];
}, 10, 2);

FSE Theme Development Process

What’s Included in the Work (Deliverables)

When you order a turnkey FSE theme, you get:

• Design system in theme.json (colors, typography, spacing)
• HTML templates for pages, posts, archives, 404, and custom post types
• Custom block patterns (hero, gallery, testimonials, etc.)
• Editor restrictions to protect layout integrity
• Site Editor documentation and access to design tokens
• Online team training (1 hour)
• 30 days of post-launch support

The deliverables include comprehensive documentation, access credentials, online training, and post-launch support.

All within timelines from 3 to 15 days depending on complexity. LCP is guaranteed to stay under 2.5 seconds. Costs start at $1,500 for basic themes, with custom solutions ranging from $3,000 to $8,000.

Pricing is custom—depends on the number of templates, design complexity, and porting needs. Get a consultation and accurate estimate: contact us. We guarantee the FSE theme will meet modern performance and security standards. Order an FSE theme to gain full control over your site without being dependent on a developer.

WordPress Development: Custom Themes, Plugins, and WooCommerce

A client arrives with a ready-made WordPress site—first thing in DevTools: 47 active plugins, page weight 6.8 MB, TTFB 2.4 s, five conflicting jQuery versions in the console. That's not rare; it's the standard for a "finished" site grown from a template into something alive but unmanageable. We solve such problems end-to-end—from audit to deployment. Get in touch—we evaluate your project in one business day.

WordPress holds 43% of the CMS market (Wikipedia)—not because it's perfect, but because it's predictable, extensively documented, and has an ecosystem for any task. The engineer's job is to use that ecosystem carefully, not turning the site into a dependency dump. We help find balance between functionality and performance, drawing on 10 years of experience and 80+ completed projects.

What are common architectural problems in WordPress?

Render-blocking from plugins

Plugin A loads jQuery 3.6, Plugin B loads jQuery 1.12, the theme has its own jQuery Migrate. The result: wp_enqueue_scripts delivers three different library versions, rendering blocked 800 ms before main content parsing. Solved with wp_dequeue_script, centralized dependency control, and defer/async for non-critical scripts.

N+1 queries and their solution

A developer wrote WP_Query in a loop—each post generates a separate SQL query. On a page with 20 posts, that's 21+ database queries. MySQL lags, server heats. Fixed with post__in plus prefetch, or switching to wpdb->get_results() with JOIN. Query Monitor is the first diagnostic tool.

WooCommerce under load

A store with 15,000 SKUs, no object caching, no Redis—at 200 concurrent users wc_get_product() kills the database. WordPress transients don't help: they write to DB, increasing load. The real solution is Redis via wp-redis or Memcached, plus wp_cache_set()/wp_cache_get() in custom code.

How to choose architecture: headless or monolithic?

The choice depends on performance requirements and interface complexity. Headless (REST API / WPGraphQL + Next.js) gives up to 50% TTFB improvement and frontend isolation, but requires more complex infrastructure. Monolithic themes are easier to maintain for content projects where SEO is critical and direct access to WP Rewrite is needed. We help determine the optimal option during audit. Switching to headless improves LCP by 2.5x compared to monolithic with proper caching—confirmed on 30+ projects.

How do we push LCP under 2.5s for production WordPress sites?

Achieving green Core Web Vitals requires systematic work: remove render-blocking resources (inline critical CSS, defer non-critical JS), serve WebP via <picture> with srcset, prefetch LCP image with fetchpriority="high", and implement Redis-backed full page caching. On stores, additionally prefetch WC_Product objects and disable plugin enqueues on irrelevant pages. Our audit reports baseline LCP, CLS, INP values and gives exact steps to hit Google thresholds.

Stack and approaches in WordPress development

Theme development. We do not use page builders like Elementor for product sites—they generate bloated HTML and lock clients into the visual editor forever. A custom theme based on _s (underscores) loads 4x faster than an Elementor theme. Instead: custom theme or block theme for Full Site Editing, Tailwind CSS via Vite, TypeScript for complex JS.

Gutenberg and block development. Since WordPress 5.0, Gutenberg is not just an editor—it's a platform. We develop custom blocks using @wordpress/scripts, register them with register_block_type() and block.json. Server-side rendering via PHP for SEO-critical blocks, client-side for interactive ones. Inner Blocks for composite components.

REST API and headless. WordPress as headless CMS via WP REST API v2 or WPGraphQL. Typical setup: WordPress on subdomain cms.example.com, Next.js frontend on main domain. ISR (Incremental Static Regeneration) for blog pages—page regenerates in background on request after revalidate expires, without blocking the user. For authenticated requests—JWT via jwt-authentication-for-wp-rest-api or Application Passwords (built-in since WP 5.6). More about REST API—Wikipedia.

WooCommerce. Extend via hooks and filters—never modify core files. Custom product types via WC_Product extension. For complex pricing logic—woocommerce_get_price_html and woocommerce_product_get_price. Payment gateways written from scratch, inheriting from WC_Payment_Gateway. Integration with 1C via CommerceML or custom REST endpoint.

Performance. Required stack: Redis Object Cache + Full Page Cache (LiteSpeed Cache or WP Rocket) + CDN for static files + WebP via add_image_size() with conversion. Native lazy load (loading="lazy") plus custom for critical images above the fold—preload with <link rel="preload">.

Case study: WooCommerce store, LCP 9.2s → 1.8s

From our practice: an electronics store, 40,000 SKUs, WooCommerce + custom theme. PageSpeed Insights: LCP 9.2s, CLS 0.41, INP 680ms.

Diagnosis:

• Hero image 3.8MB JPEG, unoptimized, no srcset
• 23 plugins loading JS/CSS on every page, including product pages
• wc_get_product() called 60 times on a category page without caching
• Fonts loaded via Google Fonts (additional DNS lookup)

What we did:

• Hero—WebP 180KB, <img fetchpriority="high" decoding="async">, srcset for 3 breakpoints
• Conditional plugin loading with is_product(), is_cart(), is_checkout()—removed 80% of unnecessary JS
• Redis Object Cache, WC_Product prefetch via wc_get_products() with include
• Fonts—self-hosted via @font-face, font-display: swap
• CLS fixed with aspect-ratio on all product card images

Result: LCP 1.8s, CLS 0.04, INP 140ms. Core Web Vitals—green. Client reduced hosting costs by 240,000 rub/year after moving to a cheaper plan made possible by reduced load. Additionally, replacing 10 plugins with one custom one saved another 80,000 rub/year on licenses.

Work process

1. Audit and analytics. Analyze existing codebase, competitors, technical requirements. For new sites—semantic core, UX prototyping.
2. Architecture. Decide: monolithic or headless. Define Custom Post Types, Custom Fields (ACF or native register_meta()), taxonomies.
3. Development. Local environment: Docker (nginx + php-fpm + MariaDB). Git with pre-commit hooks for PHP CS Fixer and ESLint. Deployment via WP-CLI + SSH or Buddy.works CI/CD.
4. Testing. PHPUnit for custom plugins. Playwright for E2E critical scenarios (add to cart → checkout → confirmation). Lighthouse CI in pipeline—fail if Performance Score < 85.
5. Deploy and support. Staging via WP Stagecoach or manual clone. Monitoring—UptimeRobot + Sentry for PHP errors. Plugin updates—via WP-CLI in test environment first.

What you get as a result

• Fully custom theme or modification of existing one
• Configured object caching (Redis/Memcached) and Full Page Cache
• Optimized media files (WebP, srcset, lazy load)
• Code structure documentation and update instructions
• Training for content managers on Gutenberg blocks
• 30-day uptime guarantee after deployment
• Access to repository with full change history

Timeline benchmarks

Pricing is calculated individually after requirements audit. Contact us for a preliminary estimate.

Common mistakes in WordPress development

• Directly editing theme files—all changes lost on theme update. Use a child theme or fully custom theme.
• update_post_meta() in a loop—each call is a separate UPDATE. For bulk operations use $wpdb->update() or update_metadata_by_mid().
• Disabled WP_DEBUG during development—hidden PHP Notices clutter error log and often indicate real issues.
• Storing media in Git—wp-content/uploads in .gitignore, sync via WP-CLI media import or rsync.
• No limit on WP_Query—posts_per_page => -1 on a page with thousands of posts guarantees a timeout.

Why trust WordPress development to professionals?

We have been on the market for over 10 years, completed 80+ projects, hold certifications from Automattic, and have experience with WooCommerce on high-traffic sites. Our solutions account for all nuances: from plugin compatibility to Core Web Vitals requirements (Google recommendations). After project completion you get a documented, tested, and scalable platform.

For a consultation and evaluation of your project—contact us. We respond within one hour during business hours. Get a free preliminary audit today.