What version of WordPress do I need for theme.json?

WordPress 5.8 introduced basic theme.json support with version 1. For full feature support including version 2 specifications, you need WordPress 5.9 or higher. Advanced features like fluid typography require WordPress 6.1+. As of October 2025, we recommend running WordPress 6.5+ for the best theme.json experience and security updates.

Can I use theme.json with classic themes?

Yes! theme.json works with both classic and block themes. However, classic themes will only benefit from editor color palettes and typography settings. Block themes get the full feature set including global styles, template editing, and complete design system integration. If you're using a classic theme with Gutenberg blocks, adding theme.json is highly recommended for consistent block styling.

Will theme.json slow down my website?

No, theme.json actually improves performance. WordPress generates CSS variables from theme.json during the build process and caches them efficiently. This eliminates the need for multiple PHP functions executing on every page load. In benchmark tests, sites using theme.json show 5-15% faster page render times compared to traditional PHP-based theme configuration.

How do I migrate from functions.php to theme.json?

Start by identifying all add_theme_support() calls in your functions.php related to colors, font sizes, and editor features. Convert these to their theme.json equivalents in the settings object. Test thoroughly in a staging environment before deploying. You can run both systems simultaneously during migration—theme.json takes precedence over functions.php declarations.

Can ACF Blocks use WordPress block supports from theme.json?

Absolutely! When you register an ACF block with supports for color, typography, or spacing, these controls automatically respect the constraints defined in theme.json. Users will only see the color palette, font sizes, and spacing units you've defined. This is one of the most powerful aspects of the ACF and theme.json integration.

What happens if I have both theme.json and Site Editor changes?

WordPress uses a layered approach. Your theme.json provides the base configuration, and Site Editor changes (stored in the database as Global Styles) layer on top. Site Editor modifications take precedence but cannot override permissions you've disabled in theme.json. For example, if you set custom: false for colors, users cannot add custom colors even through the Site Editor.

How do I test theme.json changes safely?

Always use a staging environment or local development setup. Create a backup of your working theme.json file, then make changes incrementally. Test each change in the Site Editor before committing to production. Use browser DevTools to inspect generated CSS variables and verify they match expectations. Enable WP_DEBUG mode to catch JSON syntax errors immediately.

Can I use theme.json with page builders like Elementor?

Partial compatibility. Page builders like Elementor, Divi, and Beaver Builder use their own design systems and largely bypass theme.json. However, if your site uses a mix of block editor pages and page builder pages, theme.json will still control block editor pages. Some newer page builders are adding theme.json compatibility, but traditional page builders operate independently.

Where can I find comprehensive theme.json documentation?

The official WordPress Developer Resources at developer.wordpress.org/block-editor/how-to-guides/themes/theme-json/ provides the most up-to-date documentation. The theme.json schema reference at schemas.wp.org shows all available properties. For practical implementation guidance and WordPress development best practices, consult with experienced theme developers.

Is theme.json the future of WordPress theming?

Yes. WordPress is heavily invested in block-based themes and the Full Site Editing experience, with theme.json as the cornerstone. The WordPress core team continues expanding theme.json capabilities with each major release. While classic themes will remain supported, new features and improvements are focused on the block theme ecosystem. For any new WordPress project starting in 2025 or beyond, using theme.json is strongly recommended.

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