# Defer Async > Use when reviewing templates, rendered HTML, or shared components related to Load scripts with defer, async, or type=module. Validate the final browser-facing markup, not just the source framework abstraction. - Skill: `thedaviddias/defer-async` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add thedaviddias/defer-async` - Raw SKILL.md: https://api.skillmd.com/api/skills/thedaviddias/defer-async/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Web & Frontend - Author: thedaviddias (https://skillmd.com/u/thedaviddias) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/thedaviddias/defer-async --- # Load scripts with defer, async, or type=module A plain <script> tag in the document head blocks all HTML parsing until the script downloads, parses, and executes. On a slow network this can add seconds of white-screen time before any content renders. defer and async allow the browser to continue parsing HTML while the script downloads, reducing Time to First Contentful Paint dramatically. ## Quick Reference - defer downloads in parallel and executes after HTML parsing, in order — use for most scripts - async downloads in parallel and executes immediately when ready — use for independent scripts - type=module always defers and enables ES module syntax - Never place scripts in without defer or async ## Check Find all script tags in this HTML file. Flag any in the without defer or async, and any at the bottom of that could be in with defer. ## Fix Add defer or async to script tags in the document head, or convert to type=module where ES modules are used. ## Explain Explain the difference between defer, async, and type=module script loading, and when to use each. ## Code Review Review templates, server-rendered HTML, and shared components that output markup related to Load scripts with defer, async, or type=module. Flag exact elements, attributes, and routes where the rendered HTML violates the rule. --- For full implementation details, code examples, and framework-specific guidance, see `references/rule.md`. Rule page: https://frontendchecklist.io/en/rules/html/defer-async