Extending Core Blocks with Frontend Interactivity: HTML API & Interactivity API

Important Notice: This will be a hands-on, workshop-style event. We recommend bringing a laptop equipped with an IDE or code editor such as VS Code or Cursor, along with a tool for quickly setting up a local WordPress installation, like WordPress Studio. If you’re unable to bring a laptop, don’t worry, you’ll have the opportunity to team up with other attendees so you can follow along and work together.

The Interactivity API is a standard system of directives based on declarative code for adding frontend interactivity to blocks-natively, without relying on external JavaScript libraries.

The HTML API is a powerful set of low-level tools introduced in WordPress core that allows developers to safely parse, inspect, and manipulate HTML on the server side. At the heart of this API is the WP_HTML_Tag_Processor, which makes it easy to modify block markup in a structured and reliable way.

In this workshop, we'll explore how to combine the Interactivity API and HTML API to bring dynamic, frontend behavior to WordPress core blocks and patterns, without leaving the WordPress ecosystem.

You’ll learn how to enhance core blocks (like core/paragraph and core/image) by extending their native markup with Interactivity API directives, enabling HTML elements to "react" to changes in the internal state managed by WordPress itself. And all of this, orchestrated by minimal custom JavaScript, without any third-party frameworks.

We’ll walk through:

• How to use the HTML API to programmatically modify block markup during server-side rendering in a safe, forward-compatible way.
• How the Interactivity API offers a declarative approach to frontend behavior, with built-in state management and routing.
• How to build rich, dynamic user interfaces, like sliders, tabs, filters, and AJAX components, using only native WordPress tools.

This session is ideal for WordPress developers with a basic understanding of HTML, PHP, and JavaScript, who are familiar with the block editor and want to build modern, interactive experiences while staying fully within the core WordPress framework.