| name | htmx |
| description | Implements HTMX interactions, configures swap behaviors, debugs hx-* requests, and builds hypermedia-driven UI components. Use when tasks involve hx-* attributes, HTMX AJAX requests, swap strategies, server-sent events, WebSockets, or hypermedia-driven UIs. |
HTMX
Use this skill for HTMX implementation and integration. Covers htmx 2.x (current stable) and htmx 4.x (beta). Reference files are annotated with [htmx 4], [htmx 4 change], and [htmx 4 removed] admonitions. Read only the reference file(s) needed for the task.
Quick Start
- Identify the domain of the task (attributes, requests, swapping, events, patterns).
- Open the matching file from
references/.
- Implement using HTML-first, hypermedia-driven patterns.
- Validate that server responses return HTML fragments, not JSON.
Minimal example — a button that loads content via GET:
<button hx-get="/contacts" hx-target="#results" hx-swap="innerHTML">
Load Contacts
</button>
<div id="results"></div>
The server endpoint (/contacts) must return an HTML fragment, not JSON:
<ul>
<li>Alice</li>
<li>Bob</li>
</ul>
The default swap is innerHTML — the response replaces the target's children. Use hx-swap="outerHTML" to replace the target element itself.
Critical Rules
- HTML responses - HTMX expects HTML responses from the server, not JSON
- Attribute inheritance - (v2) Most attributes inherit to children; use
hx-disinherit or unset to stop. (v4) Inheritance is explicit — use :inherited suffix to opt in. Not inherited in either version: hx-trigger, hx-on*, hx-swap-oob, hx-preserve, hx-history-elt, hx-validate
- Default swap is innerHTML - Always confirm the intended swap method
- Form values auto-included - Non-GET requests automatically include the closest enclosing form's values
- Progressive enhancement - Use
hx-boost="true" — pages must work without JS
- Escape user content - Escape all user-supplied content server-side to prevent XSS. Wrap areas rendering user-generated content with
hx-disable to prevent HTMX processing of injected attributes
- CSS lifecycle classes - HTMX adds/removes CSS classes during requests — use for transitions and indicators
- data-prefix supported - All
hx-* attributes can also be written as data-hx-* for HTML validation compliance
- Stop polling with HTTP 286 - Server returns status
286 to stop every or load delay polling. Always use 286 for poll termination, not conditional client-side logic
- Error swaps - (v2) Non-2xx responses are not swapped by default — add an
htmx:beforeSwap listener to enable. (v4) All responses swap by default except 204/304 — use hx-status for per-code control
- Decouple with HX-Trigger headers - Use
HX-Trigger response headers to fire client-side events instead of hardcoding DOM element IDs in server responses
- Detect HTMX requests server-side - Check the
HX-Request header to serve HTML fragments for HTMX requests and full pages for direct browser requests. Set Vary: HX-Request for caching
Reference Map
- All
hx-* attributes, values, and modifiers: references/attributes.md
- Triggers, headers, parameters, CSRF, caching, CORS:
references/requests.md
- Swap methods, targets, OOB swaps, morphing, view transitions:
references/swapping.md
- Events, JS API, configuration, extensions, debugging:
references/events-api.md
- Common UI patterns and examples:
references/patterns.md
- Official extensions (WS, SSE, Idiomorph, response-targets, head-support, preload, hx-live, hx-prompt):
references/extensions.md
- Gotchas, pitfalls, and practical guidance:
references/gotchas.md
- Cross-file index and routing:
references/REFERENCE.md
Task Routing
- Adding HTMX behavior to elements ->
references/attributes.md
- Configuring how/when requests fire ->
references/requests.md
- Controlling where/how responses render ->
references/swapping.md
- Handling events, JS interop, or config ->
references/events-api.md
- Building common UI patterns (search, infinite scroll, modals, etc.) ->
references/patterns.md
- Using WebSockets, SSE, morphing, preloading, response targeting, or head merging ->
references/extensions.md
- Avoiding common pitfalls, accessibility, error handling, architecture decisions ->
references/gotchas.md
- Cross-cutting concerns or architecture ->
references/REFERENCE.md then domain-specific files
