# Htmx 4 0 0
> Build interactive web applications with htmx 4.0, a JavaScript library providing HTML attributes for AJAX, CSS transitions, WebSockets, and SSE without writing JavaScript. Use when creating dynamic user interfaces with hypermedia-driven architecture, migrating from htmx 2.x, or implementing declarative HTML patterns. Note: 4.0 is a beta release.
- Skill: `tangledgroup/htmx-4-0-0` (Agent Skill, multi-file: 6 files)
- Install (CLI): `npx skillmds@latest add tangledgroup/htmx-4-0-0`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tangledgroup/htmx-4-0-0/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: tangledgroup (https://skillmd.com/u/tangledgroup)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tangledgroup/htmx-4-0-0
---
# htmx 4.0
## Overview
htmx is a lightweight JavaScript library that lets you access modern browser features (AJAX, WebSockets, SSE) directly from HTML using attributes like `hx-get`, `hx-post`, and `hx-trigger`. It follows the original web programming model: the server sends HTML in response to user actions, and htmx swaps that HTML into the DOM. This is called **HATEOAS** (Hypertext As The Engine Of Application State).
htmx 4.0 is a major release built on the `fetch()` API (replacing XMLHttpRequest), with explicit attribute inheritance, improved extension architecture based on event hooks, and enhanced swap strategies including morph-based updates via [idiomorph](https://github.com/bigskysoftware/idiomorph).
Key characteristics:
- Single JavaScript file, no dependencies, no build step required
- ~14KB minified+gzipped
- HTML responses from the server (not JSON)
- Declarative — behavior lives in HTML attributes
- Progressive enhancement friendly
- Supports extensions for SSE, WebSockets, preload, and more
## When to Use
- Building dynamic web interfaces without JavaScript frameworks
- Implementing AJAX requests declaratively from HTML
- Creating server-driven UIs where the server controls rendering
- Integrating WebSockets or Server-Sent Events with HTML
- Migrating from htmx 2.x to htmx 4.x
- Replacing JavaScript-heavy SPAs with hypermedia-driven architectures
- Adding interactivity to existing HTML pages with minimal code
## Installation / Setup
htmx is a single JavaScript file with no dependencies. No build step required.
### CDN (recommended for quick start)
```html
```
### ES Module
```html
```
### npm
```bash
npm install htmx.org@4.0.0-beta2
```
```javascript
import 'htmx.org';
// or named import:
import htmx from 'htmx.org';
```
### Self-hosted
Download `htmx.min.js` and include it in your ``:
```html
```
### htmax (bundled extensions)
The `htmax.js` file bundles htmx with the most popular extensions in a single file: SSE, WebSockets, preload, browser-indicator, download, optimistic, and targets. Extensions are automatically available without separate loading.
```html
```
## Core Concepts
### Hypermedia Controls
HTML has two native elements that issue HTTP requests: `` (GET) and `